Anıl Çelik ESOGÜ
  Abrazif Jet İşleme
 

 

Presumably, since you are at this web site, you have heard of waterjets already.  But in case you have not:  Waterjets (and Abrasivejets) are quickly becoming a new "standard tool" in machine shops around the world.  This is because they are fast, flexible, reasonably precise, and in the last few years have become friendly and easy to use.  They use the technology of high pressure water being squirted through a small hole to concentrate an extreme amount of energy in a small area to cut stuff.
 
"A machine shop without a waterjet, is like a carpenter without a hammer - Sure the carpenter can use the back of his crow bar to hammer in nails, but there is a better way..."
You have already heard the terms "Waterjet" and "Abrasive jet".  It is important to understand that Abrasive jets are not the same thing as water jets, although they are nearly the same. Water Jet technology has been around since the early 1970s or so, and abrasive jets extended the concept about 10 years later.
Both technologies use the principle of pressurizing water to extremely high pressures, and allowing the water to escape through a very small opening (typically called the "orifice" or "jewel").
Water jets use the beam of water exiting the orifice (or jewel) to cut soft stuff like diapers and candy bars, but are not effective for cutting harder materials.

(Above: Pure-water "Waterjet". Graphic waterjet nozzle courtesy of OMAX Corporation )
The inlet water is typically pressurized between 20,000 and 60,000 Pounds Per Square Inch (PSI).  (Or 1300 - 4000 "bar" if you prefer metric). This is forced through a tiny hole in the jewel, which is typically 0.007" to 0.015" in diameter (0.18 - 0.4mm)  This creates a very high velocity beam of water!
Abrasive jets use that same beam of water to accelerate abrasive particles to speeds fast enough to cut through much harder materials:
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(Abrasivejet graphic courtesy of OMAX Corporation )
(Left): A diagram of an abrasive jet. Notice that it is just like a water jet with more stuff underneath the jewel. The high velocity water exiting the jewel creates a vacuum which sucks abrasive from the abrasive line, which mixes with the water in the mixing tube to form a high velocity beam of abrasives.
(Right): An actual photograph of the same nozzle, with the guard removed, cutting out some parts.
People often incorrectly use the word "waterjet" when they really mean "abrasivejet".  Also, people sometimes say "abrasivejet", "abrasive waterjet", or "AWJ", which mean the same thing.  Don't worry.  If you accidentally call an "abrasivejet" a "waterjet". Nobody will laugh at you, as it is fairly common to do so.  Likewise, their are multiple spellings for the terms "water-jet", "waterjet", "water jet", etc.  I'm not fully sure which is "proper", so you will see that I use them all, depending on my mood. 
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Above: On the left is a typical waterjet nozzle.  On the right is an abrasivejet nozzle.  On the far right is a picture of an abrasive nozzle installed on a machine.  The white tube protruding from the side of the abrasive nozzle is where the abrasive comes in from, and is a dead give-away that it's an abrasivejet you are looking at.
Which nozzle is best for my material?

Water Jet Nozzle
AbrasiveJet Nozzle
Soft rubber
Hardened tool steel
Plastic
Foam
Titanium
Nylon
Extremely thin stuff like Foil
Aluminum
Graphite
Carpet
Hard Rubber
Many ceramics
Paper and cardboard
Stone
Carbon Fiber
Soft Gasket material
Inconel®
Composites
Candy bars
Hastalloy
mild steel
Diapers
Copper
Stainless Steel
Soft, or thin wood
Exotic materials
Kevlar
...All sorts of other soft stuff
Hard, or thick Wood
Granite
Glass (even bullet proof!) 
Mixed materials
Marble
Brass
In Fact, there are very few materials that abrasivejets can't cut!

Note: Many machines let you swap nozzles in a matter of minutes. Alternately, you can simply turn off the abrasive, and get a somewhat inefficient water jet from your abrasive jet nozzle.
Cost comparison:
Complete water jet nozzle assemblies cost around $500.00 - $1000.00 (US), while abrasive jet nozzles cost from $800 - $2000. The abrasive nozzle also requires support hardware for abrasive feed which can cost anywhere from $500 to $2,000(?). (I haven't done enough comparison shopping to be very accurate with the above figures.) Cost of operation is much higher for the Abrasive jet because of mixing tube wear, and abrasive consumption.
Limitations to water only nozzles:
The only problems that you will find with a water only nozzle will be with the jewel (the orifice with the tiny hole that the water squirts through).
Jewels can crack, plug, or form deposits on them. Cracking and plugging happens as a result of dirty inlet water, and is easily avoided with proper filtration. Deposits accumulate gradually as a result of minerals in the water. Depending on your water supply, slightly fancier filtering may be necessary. Jewels are easily replaced in about 2 - 10 min., and are cheap ($5-$50). There are also diamond orifices for sale for $200.00 and up. Diamond orifices, however are not necessarily as good as sapphire ones because of manufacturing difficulties (though diamonds are getting a lot better.) The geometry of the jewel is critical to performance, and these geometry's are difficult to make from diamond.  What is best really depends on your operating philosophy, availability, and cost.
Limitations of Abrasive Jet nozzles:
Despite their simple design, abrasive jet nozzles can be troublesome at times.  There are many designs, but they share the same problems:
 
·         Short life of an expensive wear part: The mixing tube. Like I said, the abrasive jet can cut through just about anything - including itself. This will be a large part of your operating cost. (more on operating cost later) 
·         Occasional plugging of mixing tube: Usually caused by dirt or large particles in abrasive.  (This used to be a big problem with abrasivejet nozzles, but not so much any more.)
·         Wear, misalignment, and damage to the jewel.
What other components make up a typical abrasivejet / waterjet machine?
A typical abrasivejet machining center is made up of the following components:



High pressure water starts at the pump, and is delivered through special high pressure plumbing to the nozzle.  At the nozzle, abrasive is (typically) introduced, and as the abrasive/water mixture exits, cutting is performed. Once the jet has exited the nozzle, the energy is dissipated into the catch tank, which is usually full of water and debris from previous cuts.  The motion of the cutting head is typically handled by an X / Y axis structure.  Control of the motion is typically done via a computer following the lines and arcs from a CAD drawing.

As with automobiles, there are loads of other accessories and options, such as automatic tank clean-out systems, water recyclers, special tilting heads, fixturing, or motorized Z axis, etc., but the above compromise the basic system, and pretty much everything you need for making most 2 dimensional parts.
Advantages to abrasive jet machining:
Extremely fast setup and programming
No tool changes required, so there is no need to program tool changes or physically qualify multiple tools. For some systems, programming simply involves drawing the part. If you customer gives you that drawing on disk, half the battle is won.
This means that (for some machines) you can make good money off single part and low volume production!
Very little fixturing for most parts
Flat material can be positioned by laying it on the table and putting a couple of 10 lb weights on it. Tiny parts might require tabs, or other fixturing.  At any rate, fixturing is typically not any big deal.
Machine virtually any 2D shape (and some 3D stuff)
Including tight inside radii, Make a carburetor flange with holes drilled and everything. Some exotic machines are capable of 3d machining, (robot arms, (x,y) machines with lathe axis, and (x,y)-(u,v) axis machines).  (3D machining is especially tricky, however, due to issues regarding control of a "floppy tool".  For this reason, 3D machining is reserved strictly for specialty applications.).  In other words, abrasivejets are exceptional at 2D machining, but limited in 3D capability.
Pictured here is a dragon machined from 1" thick bullet proof glass, and inlay of marble and granite. Notice the fine detail possible. (picture courtesy of OMAX corp.)
Very low side forces during the machining
This means you can machine a part with walls as thin as .025" (0.5 mm) without them blowing out. This is one of the factors that make fixturing is so easy.  Also, low side forces allow for close nesting of parts, and maximum material usage.
Almost No heat generated on your part
You can machine without hardening the material, generating poisonous fumes, recasting, or warping.  You can machine parts that have already been heat treated with only a tiny, tiny decrease in speed. On piercing 2" (50mm) thick steel, temperatures may get as high as 120 degrees F (50 C), but otherwise machining is done at room temperature.

Aerospace companies use abrasivejets a lot because of this.
No start hole required
Wire EDM, eat your heart out. Start holes are only required for impossible to pierce materials. (Some poorly bonded laminates are about the only materials I can think of off hand)
Machine thick stuff
This is one huge advantage Abrasive jets have over lasers.
While most money will probably be made in thickness' under 1" (25mm) for steel, It is common to also machine up to 4" (100mm). I don't know the actual limit to thickness, but cutting speed is a function of thickness, and a part twice as thick will take more than twice as long. I have heard of people making low tolerance parts and roughing out metal up to 5-10" thick (125mm-250mm), but those people are very patient, and probably have no other way to do it.  Typically, most money is made on parts 2" (50mm) thick or thinner.
Pictured here is a 2" (50mm) thick piece of 304 stainless steel. In 1993 when I first cut this part, It took just under 3 hours with a very small 10 horsepower pump and old control software to machine this to a tolerance of +/-.005" (0.125mm).   Today, using a 40 HP direct drive pump, and modern control software, this could be machined to the same tolerance in under an hour (including programming, setup, etc.) .  (picture courtesy of OMAX corp.)
Environmentally friendly
Green Peace does not like some of those other tools in your shop. Not much of an issue now, but in the future I would expect the pressure will be on. (I was at Houstex '96 where Green peace "attended" as well.) There will be nothing to machine if our ecosystem collapses and all your customers die. Short of hand tools, abrasive jets provide the most environmentally friendly machining around. (Some of the pumps even use vegetable oil for assembly lube because waterjets are used in the food industry).
As long as you are not machining a material that is hazardous, the spent abrasive and waste material become suitable for land fill. The red color of garnet abrasive also looks nice in your garden. If you are machining lots of lead or other hazardous materials, you will still need to dispose of your waste appropriately, and recycle your water.  Keep in mind, however, that very little metal is actually removed in the cutting process.  This keeps the environmental impact relatively low, even if you do machine the occasional hazardous material.
Your clippings are valuable
When machining or roughing out expensive materials such as titanium, your scrap still has value. This is because you get chunks, not chips. You can also get more parts from the same material because of the abrasive jets low kerf width.
There is only 1 tool
There is no need to qualify multiple tools, or deal with programming tool changes. Programming, Setup and Clean up time is reduced significantly, meaning you make more money because you can turn more parts faster.
Myth Buster: Wow! you can cut 6" (150mm) thick Tool Steel with Water!?
Nope! If you are seeing 6" (150mm) thick steel being cut on a "waterjet", what you are really looking at is an "abrasivejet".  The water is accelerating the abrasive.  The steel is being cut by the abrasive, not the water!
Life of Cutting Nozzles:
Another myth: There are big differences between sapphire and Ruby jewels.
Sapphire and ruby jewels are virtually identical except in their color. The reason rubies are red is because of high chrome content vs. sapphires which have high iron content.  Both are the same mineral corundum.  If you are still concerned with jewel life, buy a diamond jewel, not a ruby or sapphire. Or better yet, buy a good water filtration system.  (Poor water quality causes mineral deposits and other problems with jewels and other high pressure components.)
How long will a mixing tube last?
A "worn" mixing tube is like a worn tool bit: It is difficult to say when a mixing tube is fully worn, but as it wears, it becomes a less effective cutting tool. (although once it starts to go bad, the wear rate accelerates). For precision work, a new mixing tube performs better than a used one.  How long a mixing tube will last depends on a number of factors, including the sales person that you talk to.  Numbers from 20 to 80 hours are fairly typical, although it is possible that they may wear faster, or last longer, depending on circumstances.
So what's the real cost?
When looking at costs such as mixing tubes and jewels that are expensive wear parts, consider the "total cost of operation", and compare it with the productivity of the machine.  When you make such a comparison you will quickly see that an abrasivejet will probably be the most profitable machine tool in your shop - by far.  Consider that your operating cost of the machine will vary between $20 and $35 per hour, but for "typical" jobs you will earn between $80 and $150 per hour, with $120/hour being quite typical*.  
* I have also seen shops do special work at prices between $500 and $2000 per hour.  Although not the norm, I occasionally see shops that find some niche market that cannot be done any other way, or where the alternate methods are very expensive.  These guys make loads of money, and often are quite secretive about how they do it.  
Obtainable tolerances:
You need a machine with good precision to get precision parts, but there are many other factors that are just as important. A precise machine starts with a precise table, but it is the control of the jet that brings the precision to the part.  A key factor in precision is software - not hardware.  This is also true for cutting speed.  Good software can increase cutting speeds dramatically.  This is because it is only through sophisticated software that the machine can compensate for a "floppy tool" made from a stream of water, air, and abrasive.
Obtainable tolerances vary greatly from manufacturer to manufacturer.  Most of this variation comes from differences in controller technology, and some of the variation comes from machine construction.  Recently, there have been significant advances in the control of the process allowing for higher tolerances.  A machine from 1990  may be capable of tolerances of 0.060"-.010" (1.5mm-0.25mm) Today, some machines are capable of making some parts +/- 0.001" (0.025mm), or even better in special circumstances (though +/-0.002" is perhaps more realistic).
When purchasing a machine, be sure measure parts that come off the machine you are going to buy.  Some manufactures stretch the truth a bit when quoting tolerances.  The reality of it is that Manufactures of abrasive jet equipment are in a tough spot when trying to advertise obtainable tolerances because of these and other factors:
Material to machine
Harder materials typically exhibit less taper, and taper is a big factor in determining what kind of tolerances you can hold.  It is possible to compensate for taper by adjusting the cutting speed, and/or tilting the cutting head opposite of the taper direction. 
Material thickness
As the material gets thicker, it becomes more difficult to control the behavior of the jet as it exits out the bottom. This will cause blow-out in the corners, and taper around curves.  Materials thinner than 1/4" (6mm) tend to exhibit the most taper (which is perhaps the opposite of what you might expect.), and with thicker materials, the controller must be quite sophisticated in order to get decent cuts around complex geometry.
Accuracy of table
Obviously, the more precise you can position the jet, the more precise you can machine the part.  Generally speaking, though, it is much easier to find precise tables, than it is to find machines that can make precise parts.  (More on why this is in "control of the abrasivejet" below.)
Stability of table
Vibrations between the motion system and the material, poor velocity control, and other sudden variances in conditions can cause blemishes in the part (often called "witness marks"), as shown in a severe case below:



The hardware that is out there varies greatly in stability and susceptibility to vibrations.  If the cutting head vibrates relative to the part you are cutting, then your part can be ugly.
Control of the abrasive jet
Because your cutting tool is basically a beam of water, it acts like a "floppy tool". The jet lags between where it first enters your material and where it exits.
Above: Bottom of jet lags behind cutting head.  The controller needs to be aware of this behavior, and compensate for it, in order to get high tolerances.
This can be a source of error in the following places:
Around curves
As the jet makes its way around a radius, the jet lag causes a tapering effect. Therefore it is necessary to slow the jet down, and let the tail catch up with the head. (And / or tilt the cutting head to compensate)
Inside corners
As the jet enters the corner, the traverse speed must slow down to allow the jets tail to catch up. Otherwise the tail lag will cause the corner to "blow out" a little.
As the jet exits the corner, the feed rate must not be increased too quickly, otherwise the jet will kick back and damage the part.
Feed rate:
When the jet slows down, its kerf width grows slightly.
Acceleration:
Any sudden movement (like a change in feed rate) will cause a slight blemish as well.  Thus for highest precision it is necessary to control the acceleration as well as feed rate.
Nozzle Focus
Some nozzles produce more taper than others. Longer nozzles usually produce less taper. Smaller diameter nozzles also produce less taper.  Holding the nozzle close to the work piece produces less taper as well.
Speed of cutting:
Typically, the slower the cutting, the higher the tolerance.  This is because as the cutting is slowed down, the surface finish improves, and the taper begins to disappear.  However in some cases it is possible to slow the cutting down so much that tolerances begin to get worse due to reverse taper.
Active taper compensation:
Some newer machines now have the option of tilting the cutting head against the taper.  This can be used to virtually eliminate the taper, or to purposely add taper into a part.  The big advantage to active taper compensation is that taper can be reduced without having to slow the cutting down. ("Taper" is when the edge of the part is not 100% perpendicular.)  I have an entire page dedicated to this topic elsewhere in this web site.  If you want to go there now, click here.
Kerf width
Kerf width, which is the width of the cutting beam, determines how sharp of an inside corner you can make. About the smallest practical abrasivejet nozzle will give you a kerf width of .020" (0.5mm) in diameter. Higher horsepower machines require larger nozzles, due to the amount of water and abrasive that they flow through.
Some waterjet (water only) nozzles have very fine kerf widths (like .003" / 0.076mm).  Likewise, it is possible to make ultra-small abrasivejet nozzles, but they are problematic.

Kerf width is typically compensated for by the controller by specifying a "tool offset", where the jet is moved 1/2 of it's diameter away from the edge of the part when it cuts.
Consistency of Pump Pressure
Variations in waterjet pump pressure can cause marks on the final part. It is important that the pump pressure vary as little as possible while machining is in progress to prevent these. (This becomes an issue only when looking for better than +-.005" (0.125mm) tolerances, however). Typically it is older Intensifier type pumps that exhibit this problem. Some newer intensifiers, and as far as I know all crankshaft driven pumps have smoother pressure delivery, and this is not an issue.
Operator experience
Abrasive jets are capable of anywhere from +-0.02" to +-0.001" (0.5mm - 0.025mm) depending on the above factors. What distinguishes one machine from another is how easy those tolerances are obtained. If you had a nozzle attached to any X,Y table capable of positioning to +-.001" (0.025mm), then, in theory, in 0.5" (13mm) thick steel, you could perhaps machine +-0.002" (0.05mm) or so. This is given either software to compensate for jet behavior, and/or an experienced operator tweaking the machine through trial and error. I have personally been able to produce parts in the slightly better than +-0.001" (0.025mm) range on an OMAX 2652, which as far as I know is the most precise machine on the market (other than an OMAX 2626xp), but that usually requires cutting the part once, measuring the error, then cutting it again, and is only possible on certain materials and geometries.
Buying a machine? Look at, and measure parts that come off the machine. Measure the first part, then cut the same part at different locations on the table to get an idea of repeatability.  Ideally, have the seller do so while you watch, to prevent cheating.  (One way to cheat is to slow the cutting way down, and another is to simply use a different machine.  It happens.)  Also, don't forget to check out the buyers guide which you can link to from the home page of this web site.
Cutting speeds:
Ideally, you want to make the most precise part possible in the least amount of time, and for the least amount of money.  Cutting speeds are a function of the the material to cut, the geometry of the part, the software and controller doing the motion, the power and efficiency of the pump making the pressure, and a few other factors such as the abrasive used:
The chart below should give you some idea of what a few typical waterjet parts might take to machine:
 

Picture
Description
Approximate Cutting time
2.5" x 2.5" Box cut from 0.5" thick mild steel
(63 x 63mm from 12mm steel)
5 minutes
the same part as above, only in 3" (76 mm) mild steel
2.25 hours
8" wide Electrical Panel cut from 0.06" mild steel
(200 mm from 1.5mm steel)
1-3 minutes
3" wide gear cut from 0.25" thick nylon
(75mm from 6mm nylon)
1.25 minutes
10" wide thingy cut from 1" thick titanium
(254 mm wide from 25 mm thick titanium)
22 minutes
7" tall horse cut from 0.25" thick aluminum
(178 mm cut from 6 mm thick aluminum)
4.8 minutes


Of course, the above times and such are totally ball-park.  How long the above parts actually take to make depend on a lot of different factors...

Here are the primary factors that determine cutting speed:
Material being cut (And how thick it is)
Hardness: Generally speaking, harder materials cut slower than soft materials.  However, there are a lot of exceptions to this.  For example, granite, which is quite hard, cuts significantly faster than Copper, which is quite soft.  This is because the granite easily breaks up because it is brittle.  It is also interesting to note that hardened tool steel cuts almost as quickly as mild steel. (Though "absolute black" granite, which is tough as nails, actually cuts a bit slower than copper.)

Thickness: The thicker the material, the slower the cut.  For example, a part that might take 1 minute in 1/8" (3mm) steel, might take a half hour in 2" (50mm) thick steel, and maybe 20 hours in 10 inch (250mm) thick steel.
Geometry of the part
It is necessary to slow the cutting down in order to navigate sharp corners and curves.  It also takes additional time to pierce the material.  Therefore, parts with lots of holes and sharp corners will cut much slower than simpler shapes.
Desired Result
If you want a high tolerance part and / or a smooth surface finish, then the part will take longer to make.   Note that you can make some areas of a part high tolerance and other areas fast, so you can mix and match to get the optimal balance between cutting speed and final part quality.
Software controlling the motion
This is probably one of the most overlooked aspects of abrasivejet machining by novice users.  You would not think that software would have much to do with the speed of cutting.  In fact, this is true if all you are doing is cutting in a straight line.  However, as soon as you introduce any complexity to the part, such as a corner, there is great opportunity for software to optimize the cutting speed. 

Below, is a part to be machined from 1/2" (12mm) mild steel:



Notice the subtle difference between the two pictures.  (The colors represent cutting speeds, with yellow being the fastest areas, and blue being the slowest.)  The part on the left took 3.3 minutes to machine, while the part on the right took 4.4 minutes to machine.  That's a 1 minute difference, or about 25%.  The difference, as it turns out, is all through software that automatically optimizes the tool path to provide the desired precision in the least amount of time.  Basically, what the software does, is looks at the geometry of the part, and then modify the feed rates and add "tweaks" to the cutting in order to squeeze the maximum amount of speed.  It does this by finding the optimal speeds and accelerations for all curves and corners, setting the optimal length and feed rate for all pierce points, adding special "corner pass" elements at corners to allow the cutting to go right past the corners where it can, etc.

When I first started working with these kinds of methods back around 1993 or so, we found that by simply optimizing the corners that we could get about a factor of two in cutting speed over a hand-optimized part.  Then, over the next 10 years or so, we added a lot more optimizations in terms of faster piercing, corner passing, improved cutting models and such, and were able to get another factor of 2 in cutting speed for some parts, while at the same time increasing the precision.

So, software matters!  And one of the most beautiful things about optimizing in software, is that it does not cost any money.  In fact, it saves money, because if you cut faster through software, you use less abrasive and put less wear and tear on all the high pressure components!
Power at the nozzle (pressure and water flow rate)
The more horsepower at the nozzle, the faster you can cut.  How much horsepower makes it to the nozzle is a function of the pressure and the orifice that it's being squeezed through.   (Note: do not confuse "horsepower" with "horsepower at the nozzle".  It is the power that actually makes it to the nozzle that is most important.  Having a big motor makes no difference, if the power all goes into wasted heat!)

Simply put,  the higher the pressure, the faster the cut.  The more water you flow, the faster the cut.   Unfortunately, as the pressure increases, so does the cost and maintenance, so this is not as simple as it seems. 

A good way to learn more about how pressure and jewel size effect cutting rates, and to calculate "nozzle horsepower" is to run the Abrasivejet Feed Rate Calculator, which you can download from this web site by clicking here.

Quantity and Quality of abrasive used
Type of abrasive: In the industry, pretty much everyone uses 80 mesh garnet for their abrasive.  However, it is possible to cut slightly faster with harder abrasives.  However, the harder abrasives also cause the mixing tube on the nozzle to wear rapidly.  So, pretty much everyone uses garnet.  It is worth mentioning that not all garnet is the same.  There are big variations between purity, hardness, sharpness, etc, that can also effect the cutting speed and operating cost.

Quality of abrasive: Typically, abrasivejets consume between 0.5 and 1 Lb (0.25 and 0.5Kg) of abrasive per minute.  There is a sweet spot for every nozzle size and pressure as to what amount of abrasive flow rate will cut the fastest, and what amount will cut the cheapest.
A shop without a waterjet is like a carpenter without a hammer - Sure you can use the back end of a screwdriver to drive in nails, but once you have the hammer, why would you ever use the screwdriver to hammer in nails?  The screwdriver still has its place, but so does the hammer.
"If you need a machine and don't buy it, then you will ultimately find you have paid for it but don't have it" - Henry Ford.

Above: machine any 2D shape with 1 tool.  Slots, radii, holes, and profile in one 2 minute setup!
I see it happen all the time:  Joe Machine Shop Owner has been looking at waterjets for 3 years, but just can't seem to make the "spooky decision" to buy a waterjet.  Finally, he gets a contract to make 20,000 of some weird and difficult part that only a waterjet can do.  He buys it to "solve a problem - he buys the machine for this one big job.  A month after the machine is installed, he isn't even using it for the "special application" that he bought it for.  Why?  Because he is too busy using it do do all sorts of "normal" machining that he took from his other machines!  Now that he knows what the machine can do, he has also got a bunch of new work from his customers.  He has found that it is way easier to use for many parts he was making on his mills / laser / EDM, punch, etc.  And he has found that he can enhance his other machining processes by doing part of the machining on the waterjet...
(I keep thinking of all the people who used to say, "What would I ever need a computer for?".)
Here are some of the benefits to using a waterjet:
  • Cheaper than other processes.
  • Cut virtually any material:
    • pre hardened steel
    • mild steel
    • exotics like Titanium, Inconel, Hastalloy
    • gummy 304 stainless
    • (most steels cut at the same speed, whether hardened, or not.)
    • Copper, Brass, Aluminum: They are a cinch!
    • brittle materials like glass, ceramic, quartz, stone.
    • laminates
    • flammable materials
  • Cut thin stuff, or thick stuff
  • Make all sorts of shapes with only one tool.
  • Cut wide range of thickness’ to reasonable tolerance up to 2” (50mm) thick
  • Up to 5” (127mm) or thicker where tolerance not important, or in soft materials.
  • No Heat Generated / No heat affected zones - this is cold cutting!
  • No mechanical stresses
  • Cut virtually any shape:
  • Fast Setup:
  • Only one tool to qualify / No tool changes required
  • Fast turn around on the machine.  Make a part, then 2 minutes be making a completely different part from a completely different material.
  • Leaves a satin smooth finish, thus reducing secondary operations
  • Clean cutting process without gasses or oils
  • Makes its own start holes
  • Narrow kerf removes only a small amount of material.
  • Your "scrap" metal is easier to recycle or re-use (no oily chips!)
  • Modern systems are now very easy to learn.
  • You can trade off tolerance vs speed from feature to feature on your part.
  • Can easily switch between high production, and single piece production, on the same machine, with no extra effort.
  • Are very safe.  (No, they don't explode, thanks to the nearly incompressible property of water.)
  • Draw the part / cut the part.  It is that easy!  Everyone in your shop can learn to use it quickly.
  • No "scaley" edges, which makes it easier to make a high quality weld
  • Machine composite materials, or materials where dissimilar materials are glued together
  • Machine stacks of thin parts all at once.

Above: Get nice edge quality from funky materials.
When comparing with Lasers:
  • Abrasive waterjets can machine many materials that lasers cannot. (Reflective materials in particular, such as Aluminum and Copper.
  • Uniformity of material is not very important to an Abrasivejet.
  • Abrasive jets do not heat your part.  Thus there is no thermal distortion or hardening of the material.
  • Precision abrasive jet machines can obtain about the same or higher tolerances than lasers (especially as thickness increases).
  • Your capital equipment costs for water jet are generally much lower than that for a laser. I.e. for the price of a laser, you can purchase several abrasivejet-machining centers.
  • Abrasive jets can machine thicker materials. How thick you can cut is a function of how long you are willing to wait. 2" (50mm) steel and 3" (76mm) aluminum is quite common. I heard of people doing up to 10" (250mm) steel, and 24" (600mm) thick glass with high horsepower systems. Once you get over 2" (50mm) thick it is very difficult to get precision, however. Lasers seem to have a maximum of 0.5" (12mm) - 0.75" (19mm).
  • Abrasive jets are safer. No burnt fingers, no noxious fumes, and no fires. (You still have to keep those fingers out of the beam.)
  • Abrasive jets are more environmentally friendly.
  • Maintenance on the abrasive jet nozzle is simpler than that of a laser, though probably just as frequent.
  • Abrasive jets are capable of similar tolerances on thin parts, and better on parts thicker than .5"
  • Abrasive jets do not loose much "focus" when cutting over uneven surfaces.
  • While lasers are often faster on thinner materials...
    • ...it may be cheaper and faster to simply buy two or three abrasive jet machining centers to do the same work
    • ...you can stack materials, so you are cutting multiple thin parts simultaneously. 
    • ...you can run additional cutting heads in parallel on a single machine
  • Modern Abrasive jets are typically much easier to operate and maintain than lasers, which means that every employee in your shop can be quickly trained to run one!
  • Abrasivejets don't create "scaley" edges, which makes it easier to make a high quality weld
  • Many shops that have lasers also have waterjets, as they are complimentary tools.  Where one leaves off, the other picks up.

Above: Much faster than EDM!  If you have an EDM, then you definitely have a need for a waterjet!
When comparing with EDM:
  • Abrasive jets are much faster than EDM.
  • Abrasive Jets machine a wider variety of materials (virtually any material).
  • Uniformity of material is not very important to an Abrasivejet.
  • Abrasive jets make their own pierce holes.
  • Abrasive jets do not heat the surface of what they machine.
  • Abrasive jets are capable of ignoring material aberrations that would cause wire EDM to lose flushing.
  • Abrasive Jet machining is useful for creating start holes for wire insertion later on. (a mill could do the job, but only after spotting the hole, changing tools to drill a pilot, then changing tools again to drill out the hole).
  • New technology allows Abrasive jets to obtain tolerances of up to +/-.003" (0.075mm) or better (I have personally done some +/-.001" (0.025mm) work, but that's the exception, not the norm, and only on certain shapes and materials.)
  • No heat affected Zone with Abrasive jets.
  • Abrasive jets require less setup.
  • Make bigger parts.
  • Many EDM shops are also buying waterjets.  Waterjets can be considered to be like super-fast EDM machines with less precision.  This means that many parts of the same catagory that an EDM would do can be done faster and cheaper on an abrasivejet, if the tolerances are not extreme.


Above: Wire EDM fixturing in an abrasivejet machining center.  This makes precision fixturing possible.  It also allows for pre-machining on the abrasive jet to release stresses in the material, and then use the exact same fixturing on the EDM to do secondary operations and final cutting to extreme tolerance.


Wow, that is a thin cut!
When comparing with Plasma / Fine Plasma:
  • Abrasivejets provide a nicer edge finish
  • Abrasivejets don't heat the part
  • Abrasivejets can cut virtually any material
  • Abrasivejets are more precise
  • Plasma is typically faster
  • Waterjets would make a great compliment to a plasma shop where more precision or higher quality is required, or for parts where heating is not good, or where there is a need to cut a wider range of materials.

Above: (Many) Modern machines are relatively clean and quiet.
When comparing with Flame cutting:
  • Abrasivejets provide a much nicer edge finish
  • Abrasivejets don't heat the part
  • Abrasivejets can cut virtually any material
  • Abrasivejets are more precise
  • Flame cutting is typically faster
  • Flame cutting is typically cheaper, if you can use it.
  • Waterjets would make a great compliment to a flame cutting where more precision or higher quality is required, or for parts where heating is not good, or where there is a need to cut a wider range of materials.

Above: Do pre-machining, and save your other tools from having to do so much work!
When comparing with milling:
  • There is only one tool to qualify on an abrasivejet
  • Setup and Fixturing typically involves placing the material on the table with an abrasivejet
  • Cleanup is much faster with an abrasivejet
  • Programming is easier and faster
  • Machine virtually any material, including:
    • brittle materials
    • pre hardened materials
    • otherwise difficult materials such as Titanium, Hastalloy, Inconel, SS 304, hardened tool steel....
  • Waterjets are used a lot for complimenting or replacing milling operations.  They are used for roughing out parts prior to milling, for replacing milling entirely, or for providing secondary machining on parts that just came off the mill.  For this reason, many traditional machine shops are adding waterjet capability to provide a competitive edge.
When comparing with Punch Press
  • Lower cost per piece for short runs
  • Place holes closer to the materials edge
  • Fast turn-around
  • Minimal setup
  • Thick materials are fine
  • Brittle materials are no problem.
  • Hard materials are easy.
  • Some stamping houses are using waterjets for fast turn-around, or for low quantity / prototyping work.  Waterjets make a great complimentary tool for punch presses and the like because they offer a wider range of capability for similar parts. For high production of thin sheet-metal, the stamp will be more p rofitable in many cases, but for short runs, difficult material, thick material, and many other similar but different applications, waterjets have their place.

Above: About 5 minutes is all it took to make this custom file!  That is some very hard material!  Consider hardening the metal before you cut it.
Abrasivejets also play a big part as just one part in a larger manufacturing process.  For example, abrasivejets are often used to machine features into an existing part, or to do pre-machining to remove material before precision finishing on other machinery.
Q: With all that pressure, are waterjets safe?
Abrasive jets and waterjets are quite safe. The nozzle is typically 0.1" (2.5mm) or so from the material, so it is difficult to get fingers under it.
High pressure tubing does not explode because water is not very compressible. When a leak occurs, the pressure quickly drops to a safe level.
Eye protection should always be worn to protect from the occasional splash of dirty  water.
Ear protection may be useful when operating some machines (though most modern machines have quieter pumps and cut underwater to keep things comfortably quiet.
   

It is, however, very foolish to check the pressure with your fingers.  A pressure gauge is usually provided for your comfort.

Q: How fast is Abrasive Jet Machining?
The speed of abrasive jet machining is a function of how much water and abrasive you push through your nozzle as well as how thick, and how hard your material is.

Thin materials cut much faster than thick materials.  Straight line cuts cut much faster than corners or curves.  Hard material cuts slower than soft material.

A typical part in 1/2" (13mm) aluminum might take 2-10 minutes to make.  In 1/2" (13mm) steel, it would be twice that time.  A 2" (50mm) thick part may take hours.  A 1/16" (1.5mm) part will cut in seconds. 

I am purposely being a little vague in my answers here, because a lot of it depends on the shape of the part, the software controlling the machine, the size and efficiency of the pump and nozzle used, and a lot of different factors.  I used to have a chart with a bunch of speeds here, but I deleted it because straight line cutting speeds are misleading, and there is a wide variety of equipment out there with different software and hardware, making it difficult to make a single chart that covers all bases without pissing somebody off.  The best way to answer this question, is to contact a manufacturer and have them make some parts for you, while you watch.  Otherwise...
Click here for info or to download Win 95 / 98 / NT / 2000 / XP Abrasivejet feed rate calculator software.   This will answer many questions regarding cutting speed in a variety of materials and pump configurations.
Remember: It is not just raw cutting speed that is important, but also programming time, setup, and tear down time.  AWJ machining offers HUGE advantages in these areas.
Waterjet (water only) cutting is usually much faster than abrasivejet cutting due to the fact that you are usually cutting very soft stuff.
If you are still curious, then be sure to contact a manufacturer of equipment and send them a drawing.  They would love the opportunity to show off what they can do.
Q: How thick can a waterjet cut?
Practically speaking 2" (50mm)  or 3" (75mm) thick steel is about the limit for an abrasive waterjet.  Some manufacturers will claim that you can go thicker than this, which is true, but misleading in many cases:
If you want to cut steel that is thicker than 3" (75mm), then you need to ask how long can you afford to wait for your part to be finished?  The thicker the material, the longer the wait, and you just have to ask yourself if it is cost effective.  Sometimes it is, but usually it is not.  In the case of exotic materials where the material is extremely expensive and difficult to cut by other means, then 3" (75mm) and thicker may be practical.  Titanium is an example of such a material.
If the cut is along a straight line, or a shallow curve, then it is also more practical to cut thick.  However, if there are sharp corners or curves, then the cutting very quickly becomes extremely slow.
For soft materials, you can cut extremely thick.  For example, you could cut 2 foot (600mm) sponge pretty easy.  For hard material, like metal, once you pass about 2" (50mm) thick, you have to really think about whether or not you are going to make money.  It is possible to make very good money, in special cases, on materials up to 5" (127mm) or 6" (152mm) thick, but I would not recommend your average machine shop to purchase a machine with the primary purpose of doing stuff over 2" (50mm) thick.
About the thickest steel I have seen anyone cut is 9".  The thickest Aluminum I have seen cut is 12", and the thickest Titanium I have seen cut is 9".  However, this is not the norm.  The aluminum piece was pretty simple, but took 20 some hours to cut.
Q: Who buys these machines anyway?
If there is one thing that I hope you come away with after visiting this web site, it is the realization that abrasive / waterjet machines are not "weird" specialty machines for niche applications.  They are general purpose tools that are useful in any machine shop / job shop .  With that in mind, here is a small sampling of specialized applications:
    • General purpose machine shops: Here is where I see the biggest growth in abrasivejet use.  This is because abrasivejets are such good all-around machine tools.  It is very quick to go from idea to finished part.  I have even found it easier to machine my own washers than to look in the parts bin for a washer of the size I need.
    • Artists: For example: Stained glass, marble and stone, metal sculpture, jewelry...
    • Architectural: Similar to the art market, there are many machines out there making custom flooring from stone, and the like, as well as architectural details from metal, etc.
    • Aerospace: Lots and lots and lots of aluminum.  Exotic metals such as Inconel®, Titanium, Hastalloy, etc.  Ceramics.  Composites...  Brackets, mounts, tooling, instrument panels, all sorts of mechanisms...
    • Manufacturing: Abrasivejets are used for making parts of products that are sold, as well as many of the parts used to make the machines on the assembly lines.
    • Automotive & transportation: Prototyping and production parts for automobiles, and the tooling for making automobiles.  Also there are a lot of custom race car parts made on waterjets.
    • "Waterjet shops": Traditional waterjet shops, of course, buy waterjets.
    • Laser shops: Lasers and waterjets are highly complementary tools.  They both pick up where the other leaves off.
    • EDM shops:  Some of the small size / higher precision abrasivejet machining centers are great complimentary tools to EDM because they allow for higher speed machining of similar shapes, and can provide other services for the EDM such as pre-drilling start holes or stress relieving the part prior to skim cutting on the EDM.
    • Model shops / rapid prototyping: Fast turn around of single piece production in nearly any material makes waterjets great for these kinds of applications.
    • Wealthy hobbyists: I have seen a few people buy them for their homes.  I want one in my garage too.
    • Schools: Many of the larger size universities that offer engineering classes also have waterjets.  They are great tools for the classroom environment because they are easy to learn, program, and operate, and because they can make one-off kind of parts quickly.  They also provide a great service to other departments within the university that may need job-shop services.
Q: What are all the different kinds of machines, and what's the investment to get one?
There are a lot of different kinds of machines.  Basically, they boil down to these :

Small / Medium / Big
Precision / Fab
2D / 3D
Standard / Specialty & Custom
  • Small machines: These are machines smaller than 2x4 feet (600x1200 mm) in size.  Typically they are used in general machine shops.  They are also popular in EDM shops, the garages of rich people, schools, etc.  If you are looking at a first machine to purchase, these are great choices because they don't cost so much, and there is little risk in purchasing one.  For example, for one particular machine that I am familiar with, the machine pays for itself if you keep it busy for only 1/2 day per week.  Whether or not you are not doing a huge volume of work, you can still make a lot of money with a small machine.
    • Advantages
      • Low cost to purchase - Payment on machine is low, so you don't need to load the machine down to pay for it.  Pays for itself very quickly, and is low risk to purchase.
      • For price of some of the big machines, you may be able to buy 2 small machines, and double your productivity.
      • Convenient layout for using "as a machine tool" for secondary machining, etc. - ergonomically, they are simply funner to use.
      • Small footprint does not take up a lot of shop space.
      • Easy to move around as your shop flooring arrangement changes
      • Easier than the larger machines to setup and install.
      • Generally offer higher precision than their larger cousins.
    • Disadvantages
      • Small cutting area (Although it is often possible on some machines to feed larger stock into the machine to cut from)
    • Investment: Complete systems* can be had forunder $80,000 .  While at first this may seem like a lot of money for a machine tool, keep the following in mind:
      • You are not buying a bunch of extra tooling
      • The machine brings in more revenue per hour than traditional tools.
      • They pay for themselves quickly.  A small machine like this can be paid for with 1 day of work per week on the machine.
  • Medium sized machines: These range from 4x4 feet to 4x8 feet (1200x1200mm to 1200x2400mm)  in size.  Sometimes they are used with multiple cutting heads, but usually not.  These are typically purchased by machine shops who do larger work, or simply want a machine that is large enough that they can fit big sheets of material. 
    • Advantages
      • Fit larger sized sheets of material into the machine
      • Some run multiple cutting heads at once
      • Smaller footprint means less space used.
      • Easier than the giants to setup and install.
    • Disadvantages
      • Expensive - Sometimes you may be better off with multiple smaller machines
      • More difficult to load / unload materials
      • Awkward to use "as a machine tool" for secondary operations and such due to their large size.
    • Investment: Complete systems* are available for around $100,000 to $200,000 , depending on options and such.
  • The Giants: These are machines that are so big that you can fit any size material you want in them.  They are sized to fit material 8x16 feet, or larger in their beds.  Typically they run multiple cutting heads, and are used in high production environments.  Large waterjet-only job shops and laser shops are typical buyers of such machines.  
    • Advantages
      • Fit huge sheets of material into the machine
      • Run multiple cutting heads at once
    • Disadvantages
      • Cost more to purchase
      • More difficult to load / unload materials
      • Awkward to use "as a machine tool" for secondary operations and such due to their large size.
      • Large enough to require specialized shipping and installation in many cases.
      • Need to have a lot of work to pay for the machine.
      • Often the tolerances on such big machines are fairly low (but this is not always the case)
    • Investment: Complete systems* are available for around $200,000 to $400,000 , depending on options and such.
  • Custom machines : There are hundreds of custom machines out there made for custom purposes.  For example, for diaper cutting, food cutting, animal mutilation, cutting automotive carpet on production lines, mining applications, eye surgery, cardboard box making, oil drilling, etc.
My idea of an ideal abrasive waterjet shop would have several small machines, one medium sized one, and one huge one running 2 nozzles.

My idea of an ideal machine shop would have a multitude of various CNC and manual machine tools along with one or two small sized abrasivejets.
*When I say "Complete systems", I mean everything you need to get a new machine, and have it running such as: the pump, xy table, nozzles, abrasive delivery system, controller, software, installation, and training.  However,  these numbers are very 'ball park".
Q: Who's machine should I buy?
I can't tell you that!  Shop around. Talk to owners, etc. Read the "waterjet buyers guide" on this web site for some tips and things to look for.  Do your homework!
Q: Are all the machines out there pretty much the same?
Absolutely not! There is a huge variety of machines out there that have widely varying capabilities in terms of speed, accuracy, ease of use, ease of maintenance, cost, and what applications they are designed for.
Q: What does it cost to run an abrasive jet?
A ball park figure for a generic machine would be very roughly $25-$30 / nozzle hour + whatever you pay your employees.
The above costs may seem high, but remember, an abrasive jet puts out a lot of parts per dollar spent.  I.e. you can charge a lot for this service.  Compare this to other machining methods, and remember to consider setup, clean up, and programming time.
Hopefully I will have a complete financial breakdown here soon, as I have seen calculations that basically say that you need to keep a small machine running for 3 or 4 days a month, and it is paid for.  The remaining days are just profit.
Q: How do abrasive jets compare with lasers?
  • Abrasive jets can machine many materials that lasers cannot. (reflective materials in particular)
  • Abrasive jets are great with Aluminum, Copper, stainless steel and other reflex metals.  These are not easy to cut with a laser, and can damage the laser.
  • Abrasive jets do not heat your part.  Thus there is no thermal distortion or hardening of the material.
  • Precision abrasive jet machines can obtain about the same or higher tolerances than lasers (especially as thickness increases).
  • Your capital equipment costs for water jet are generally much lower than that for a laser.
  • Abrasive jets can machine thicker materials. How thick you can cut is a function of how long you are willing to wait. 2" in steel and 3" in aluminum is quite common. I heard of people doing up to 10" (254mm) steel, and 24" (600mm) thick glass with high horsepower systems. Once you get over 2" (50mm) thick it is very difficult to get precision, however. Lasers seem to have a maximum of .5" - .75" (13mm-20mm).
  • Abrasive jets are safer. No burnt fingers, no noxious fumes, and no fires. (You still have to keep those fingers out of the beam.)
  • Abrasive jets are more environmentally friendly. (I hope this is a selling feature to you.)
  • Maintenance on the abrasive jet nozzle is simpler than that of a laser.
  • Abrasive jets are capable of similar tolerances on thin parts, and better on parts thicker than .5"
  • Abrasive jets do not loose much "focus" when cutting over uneven surfaces.
  • While lasers are often faster on thinner materials, it may be cheaper and faster to simply buy two or three abrasive jet machining centers to do the same work.  Also, you can stack materials.
  • Modern Abrasive jets are typically much easier to operate and maintain than lasers, which means that every employee in your shop can be quickly trained to run it.
  • You can't stay long at the same point with laser or fusion of material will occur.
  • Laser cut is under inches (near 4 inches for WJ), but can do a better job in controlling depth of cut  (ex.: cutting slot in tubing is possible with a laser, but  difficult with abrasivejet).
  • Laser has higher power consumption (power factor about 2%) (ex.: for 1 kw output you need 50 kw input for YAG) (CO2 more efficient, but less precise ray).
  • Laser needs a good "chillier" for cooling.
Q: How do Abrasive jets compare with Wire EDM?
While EDM is much more precise...
    • Abrasive jets are much faster
    • Abrasive jets machine a wider variety of materials
    • Abrasive jets make their own pierce holes
    • Abrasive jets also do not heat the surface of what they machine
Many EDM shops purchase Abrasive jets to complement their equipment, and to do pre machining.  Think of an abrasivejet as a very fast, but not very precise EDM.
 
Q: How do Abrasive Jets compare with conventional milling?
  • Setup and fixturing are much faster and when you are done, the clean-up is faster.  This means that while the mill may cut faster, you will be making more parts and more money on the abrasivejet.
  • on many AWJ systems, programming is much easier and quicker
  • there is no tool changing
  • Wear on tool is often less, especially in harder and gummier materials.
  • There is only one tool to "qualify".
  • You can get more parts out of the same material.
 
This is a part you might otherwise do on a mill. It took under 20 min to make with an abrasive jet - that includes setup & cleanup time! Actual machining time is about 6 minutes.  Material is .5" (13mm) thick hastalloy - tolerance about +/- .002" (0.05mm). (Photo courtesy of OMAX Corporation )
Q: Should I buy an abrasivejet instead of a Mill?
No.  this is like asking "should I buy a hammer instead of a saw?".  Consider an abrasivejet to be a highly complimentary tool to the other machines in your shop.  It will not necessarily replace them, but it will give you one more tool to work with.  I think that you will find this particular tool to be much more productive than you expect, once you have one.  On the other hand, if you already have mills, then by all means buy an abrasivejet!  If you have a mill, and you don't have an abrasivejet, then your tool box is incomplete.
Q: How much money can I make with an abrasive waterjet jet system?
I have seen shops charging a minimum of $100.00 per hour, I have never seen a shop lose money with this equipment, and I have personally visited at least 40 different shops. EVERY shop I have had experience with is making good money from their equipment!  $80.00 per hour is about the very cheapest I have ever seen it, $120-$135 is fairly normal, and $150.00 and up can be charged for exceptional service.  The highest I have ever seen was $2000.00 per hour, but that was a special case that is not normal.
Q: How is abrasive waterjet work priced?
A: Typically it is priced by either the time it takes to make the part, or how much the part would cost when made with conventional tools.  I have seen people charging up to $2000.00 per hour for some parts, but $100-135.00 per hour is much more typical.  I would recommend first that you look at the part to machine, and think of what it would cost on a mill, or other competing equipment.  Then price the part slightly under that, and make a good profit.  However, pricing and pricing strategies are highly dependant on your local market conditions.
Q: What can go wrong with a waterjet?
Parts can tip and snag the nozzle. (some nozzles have guards to protect them from this, but it is still a problem). Nozzles can plug. Parts wear out and need replacing. A giant meteorite could crash into the earth.
Q: Is it noisy?
Yes and No. Some systems are designed to machine submerged. This quiets the machine to a level that you can talk over. When machining above water , hearing protection is required.  Also, some pumps can be really noisy, while others are fairly quiet.
  Q: What are the advantages and disadvantages of cutting under water?
Cutting under water is a feature on many systems.  It provides two main advantages:
  • Reduced Noise
  • Reduced Mess
Most systems that allow you to cut under water, will also let you lower the water level and cut above water.  Cutting above water has some advantages:
  • You can easily see what is going on
  • Stuff that floats, won't float around
  • Your material will get less wet (somewhat)
Beginner users typically prefer to cut above water because it allows them to see the cutting process, which is both fun to watch, and also a comfort when you're not totally sure you know what you are doing.  I personally do about 80% cutting below water and 20% above water.  The times I go above water are usually when working with thin material that tends to float, or when doing something tricky where I might need to get my hands in there to remove scrap before it collides with the nozzle, etc.  I also cut above water sometimes when cutting material that is thicker than can easily be submerged (such as stuff thicker than 2").

Of course, being able to cut underwater, then lower the water quickly to check on progress, then raise the water again is a handy feature to have.

One other unusual benefit to cutting under water that is a bit counter-intuitive, is that parts rust less when submerged.  This is because being under-water prevents the constant splash of water, and then air, then water, then air, that will accelerate the rusting process over simply cutting the entire thing submerged.
Q: What about maintenance?
In the past, abrasivejets have been notorious for being a bear to maintain.  Modern equipment is much easier to maintain than even just a few years ago.  Modern equipment also requires much less maintenance than in years past.  Much progress has been made in this area, but no machine is maintenance free yet.  In fact, I would say that although very significant advances have been made, there is still a long way to go.  There are a few factors that come into play:

#1 - How the equipment is run (The harder it is run, the more frequently things break.  Obviously, this is very much a factor of the pressure the machine is run at.)

#2 - How much care is taken during maintenance.  If you rebuild in a clean-room, things will last much longer than if you rebuild in the dirt.  There are a lot of high precision components that microscopic bits of grit can easily damage.  I always rebuild my nozzles at the bathroom sink, where I can completely wash all the grit and gunk off with soap and water before re-assembly.  A tiny speck of dust underneath the jewel in the nozzle will cause the jet to shoot to the side, and cause accelerated wear of the mixing tube.
Frequency of maintenance:
Waterjets certainly require maintenance.  Expect to change nozzle parts frequently (daily).  Expect to change pump parts less frequently, but regularly enough that you wish you didn't have to.  Expect that things will break when forced to operate at 35,000 to 60,000 PSI.  That is a lot of pressure, to ask a seal to hold back!  It is also wise to keep some critical spares at hand.
Generally speaking, the higher the pressure, and the more on/off cycles the equipment sees, the more frequently it will need maintaining.
Ease of maintenance:
For the most part, anyone who can change brake pads on a car can keep an abrasive jet going with a days training and a good manual, and the occasional phone call to tech support. Mixing tubes, (part of the nozzle) wear out and are easy to replace (often similar to replacing a drill bit). Pumps will need periodic seal changes.  Depending on pump design, seals can be anywhere form relatively easy and quick to quite awkward and time consuming to replace.
Tip:
When maintaining your critical parts such as nozzle and seal components, do so with care.  Critical components are very sensitive to dirt / dust, microscopic scratches, etc.  My advice is to take these components into a different room, wash them down (often with soap and water / or ultrasonic cleaner), and then assemble them in a clean environment!
Also, if you have dirty or hard water, you will either need to maintain everything more often, or purchase a good water softener and /or filtration system.
Final word on maintenance:
You don't need to be an engineer, but if you are afraid of changing your cars spark plugs, consider hiring someone to help you.
Q: Can you control the depth of the cut?
Yes and No, but not really. If you move the machine really fast, there will not be enough time to cut all the way through. This can be useful for marking part numbers, or for other artistic purposes, but good luck trying to get any depth precision. Reducing the pressure and the amount of abrasive will gain you some more control.
(Note: Waterjet Technologies, located in Kent, WA, has a special patented process for milling that works fairly well in certain circumstances.  This technology is beyond the scope of this web site, however, as it is really only practical under specific conditions.  I have heard that other companies are working on this as well.  If you absolutely have to mill some exotic material, then there is probably some  benefit to this, otherwise, it is not a common use for this technology at this time.)
If you are interested, there is a picture of a company logo milled out of steel, and etched in glass on the pictures page of this web site.
 
Expect anywhere from +/-0.001" to 0.005" (0.025mm to 0.127mm) or so with precision equipment and most geometry's and thickness'.  If you are machining thicker than 2" (50mm), using older equipment, or equipment that is not very precise, then expect tolerances to be significantly lower, such as +/- 0.010" - 0.060" (0.25mm - 1.5mm).  Obtainable tolerances are strongly a function of the control software running the machine.
Ideally, you will want a machine that can produce the highest tolerance parts possible, as this will allow you to do more work than you otherwise could.  In other words, you want to be able to make final parts that require minimal or no secondary machining, so that you won't have to turn high precision work away.
Q: What are the Limiting factors to the precision and part quality?:
Jet Lag:
Because the abrasive jet is a "floppy tool", it tends to wander as you are machining. On straight line cutting, this translates into a "lag" as shown in this illustration:

(Graphics courtesy of OMAX Corporation )
This lag can usually be ignored when cutting in a straight line, but becomes critical when near a corner. As the jet approaches a corner, it becomes necessary to slow the motion down so the bottom of the jet can catch up to the top, and be perpendicular to your material. If you don't slow down, you will have an ugly corner indeed.
If you accelerate quickly when coming out of a corner, the jet will kick back, and mar your part.
Some modern Abrasivejet controllers compensate for this behavior automatically, which is why I say that programming is easy. There are pictures of cuts through Plexiglas on the pictures page of this web site, that demonstrate jet behavior with and without compensation.
Kerf:
Abrasive jets have a tool width that typically ranges between 0.020" (0.5mm) and 0.040" (1.0mm), depending on the mixing tube diameter. As you slow down to make a nice corner, the kerf grows slightly. The amount it grows is a function of how much you slowed down by. The amount you must slow down by is a function of your material thickness. In other words, the thicker the material, the harder it is to get precision in the corners.
Most controllers compensate for kerf width automatically, but don't fully compensate for the kerf growing as a function of speed.
Kerf width depends on the nozzle you are using.  With low horsepower pumps, you have a narrower kerf.  With high horsepower pumps, you have a larger kerf.
Lead in and Lead outs:
There will be a "booger" where you pierce the material, especially in thicker materials. For this reason, you usually pierce the material in the scrap that is to be removed, then lead in to the actual cut. Even so, it is difficult, and often impossible to avoid a small "tit" or indent in your final part. Depending on how you design your lead in/out, you can decide if you want to create a "tit" or an indent.
Taper:
Taper is the difference between the top profile of the cut verses the bottom profile. Books can be written on taper.  Basically, the biggest causes of taper are:
    • Distance of nozzle from material. The closer you can get the nozzle to the material, the less the taper.
    • Hardness of material (usually harder materials exhibit the least taper)
    • Speed of cut. Machine too fast and get taper in one direction; machine too slow and get taper in the other direction.
    • Quality of jet exiting the nozzle. The more focused the nozzle, the less taper exhibited.
    • Quality of abrasive used.  Using quality abrasive can make a big difference.
    • Thickness of material (Metals between 0.5 and 1.0" tend to have less taper than metals thinner or thicker than this range)
If you cut quickly, then the jet will not have a chance to completely remove all of the material, and you will get taper shaped like a "V".
If you cut slowly, then the jet will fan out, and "revers taper" will occur.
If you cut at just the right speed, then you may experience very little taper.
If you are cutting extremely thick parts, then you may experience "V" taper, reverse taper, or even "barrel" taper.

Top: Taper caused by a fast cut
No Taper
Taper caused by a slow cut
Bottom: Barrel Taper observed typically in thicker materials (for example, 2" steel)

It is also possible to get a combination of both barrel and other kinds of taper.

Taper can be reduced by slowing the cutting down, or eliminated by tilting the cutting head in the opposite direction as the cutting with a device such as the one below:

Above: an articulated tilting nozzle for automatic taper removal.  Devices such as this can offer great improvements in taper for the highest precision applications.
Note that it is not possible to completely elliminate "barrel" taper by tilting, so for very thick parts, some barrel will still remain, but there is still some benifit in removing the standard V shaped taper component.
Positioning system:
Obviously, you need a machine that is capable of positioning to a precision that is higher than the part you want to make.  You also don't want vibrations from your pump or other sources to effect your final part.
Control:
How well the controller is able to compensate for all of the above will make the biggest difference in precision, especially around curves and corners.  (It will also make a big difference in how quickly the parts can be made.)
Q: What are the different methods for piercing the material, and why would I use one over another?
Before we can answer the above question, it is first necessary to understand something about abrasivejet piercing:
There are a few materials that are difficult to pierce with the abrasive jet. Examples of difficult to pierce materials are: Glass, many ceramics, some stone, some laminates. In general, if you drop it on the floor and it breaks, there is a good possibility that it will be difficult to pierce. There are several work arounds that make it possible, but a little inconvenient.
For brittle materials:
    • Pierce at a lower pressure than cutting
    • And / or Place a sacrificial material on top of the material you are going to cut. (So that the abrasive is fully flowing before the jet hits the material).
Some systems allow for automatic and / or manual low pressure piercing.
In addition, thick materials are slow to pierce.  For this reason, several piercing methods have been developed:
Wiggle Piercing:
For quick clean piercing of thick material in the minimum amount of space.  "Wiggle" piercing causes the cutting head to wiggle back and forth over a very short distance while piercing.  This prevents the backwash from the jet from reducing the effectiveness of the pierce, as in a stationary pierce.  If you cut thick (>.5" (13mm)) materials this is especially important.
(As a side note, I think that I invented this method back in 1994, although it is highly likely that someone else may have also thought of it independently.  The need for wiggle piercing came about because I was using a a wimpy 10 horsepower pump, and had to cut thick materials.  Wiggle piercing enabled us to cut steel effectively up to about 2" (50mm) thick, where previously, the practical limit with such a wimpy pump was around 1/2" (13mm) thick.  A very dramatic improvement).
Dynamic Piercing:
This is typically slower than "wiggle piercing".  The jet does not wiggle, but rather slowly moves into the material, piercing as it moves. If properly implemented, dynamic piercing can be quite fast - even faster than wiggle piercing.  If not properly implemented, which is usually the case, it can be significantly slower than wiggle piercing.  (The proper speed and length of a dynamic pierce is a function of the cutting conditions and is very hard to predict, which is why it is usually slower than wiggle piercing.)
Stationary piercing:
This is a pierce that is performed without moving the nozzle.  The nozzle simply turns on, and waits until the material is pierced.  This is the method of piercing if you do not have enough room to perform a Dynamic or Wiggle pierce.  It is much, much slower, however, so is reserved only for piercing thin material or tiny holes.  In some materials and thickness, it is virtually impossible to pierce using stationary piercing.
Low pressure piercing:
For brittle materials, it is often desirable to pierce at a lower pressure than you would normally cut with.  This prevents cracking of the material. Low pressure piercing can be combined with any of the above methods.
Other piercing:
There are a handful of other methods for piercing for special (weird) circumstances, but the above are the most common methods.  (Spiral piercing, coming in from the edge of the material, pressure ramped piercing, etc.)
Q: What does the jet look like when it exits the nozzle?
Like a fire hose. The jet starts out coherent, then fans out.  When cutting thick metal, the jet will be held coherent by the metal you are cutting.
  • Click here to watch video: 56k (for slower Internet connections)
    Click here to watch video: 100k (for fast Internet connections)
Q: How much do abrasivejet systems cost?
Nothing, they pay for themselves!  Typical purchase price for a new complete 2 dimensional system with everything you need to make parts is between $80,000 to $200,000.  Prices can go up from there for custom systems, multi-axis systems, or exceptionally large table sizes.
Keep in mind that you will not have a large cost of additional tooling, as there is only one tool involved.  However, there are additional costs in consumables such as the nozzle, abrasive, plumbing, electricity, and spare parts.
Q: How far can the nozzle be from the material I am cutting?
The distance between the tip and the nozzle is normally between 0.030 and 0.060 inches (0.75mm and 1.5mm ) or so.  Having the nozzle closer to the material helps reduce taper, and give a better quality and faster cut.  However, it is possible to cut with the nozzle much further from the material, which can be useful when cutting warped plate, round tubing, or materials with small surface features in the vertical direction.  If you need tolerances greater than +/-0.005" (0.127mm), then keep it as low as you can go.  If you don't need such high tolerances, then you can go up to perhaps an inch or more, if needed for the situation.  At high stand off distances, you will also experience additional "frosting" around the top edge of the cut, and reduced cutting performance.
Q: What do I do about the stand-off if I am cutting warped material?
The simplest thing to do is to simply raise the cutting head so that it is high enough to clear the highest point on the plate.  Since you are using warped plate, you are obviously not doing high precision work, so the slight increase in cutting stand-off will have negligible effect.  

Otherwise, some machines have features for "terrain following" or automatically setting the stand-off at each pierce point, or pre-programming the Z heights along the tool path.  All of these methods have advantages and disadvantages depending on the particular circumstances.  Terrain following has it's own set of problems because of the water and garnet and tipped parts that can all intefere and make it unreliable.  In general, though, simply setting the cutting height to clear the highest point on the plate works fine.
Q: Can you stack material, and how thick?
Yes.  Stacking is often useful if the total stack height is less than 0.5" (13mm) or so.  To determine optimum stack height, simply compute the tool path for several different material thickness'.  For example, if you are cutting 1/8" aluminum, simply compute the path at 1/8", 1/4", 3/8", 1/2", 5/8", etc. and determine which stack size cuts fastest.  You will loose some precision the higher you stack, but you will gain cutting speed up to a point.  Depending on material and part geometry, the optimal stack height ranges from perhaps 1/4" to 1/2" (6 to 13mm). 
The more corners there are in your part, the shorter the optimal stack height.  This is because to maintain precision, it is necessary to slow down the machine in corners, and the thicker the stack, the more you need to slow.  In other words, optimal stack height is a function of geometry, which is why there is no "rule of thumb" to determine the optimal stack height.
Q: Can I "common line" cut in order to cut two pieces with a single cut?
Yes, but... It is often a brain-twister to make an efficient path where some features are common line cut.  In addition, the accuracy of the parts will suffer because it is difficult to compensate for the kerf width of the jet precisely without re-creating the tool path as the nozzle wears.  Common line cutting is also not practical when using tilting cutting heads for removing taper, since the taper will be removed from one side, but added to the other.   So, the answer to the question is "yes, if you are willing to do the extra programming and also willing to live with less precision."  It is perfectly reasonable to do common line cutting for low precision production work.
Q: How thick is the kerf?
Typical Kerf widths vary from a diameter of about .020" to .060" (0.5mm to 1.5mm) .  With higher horsepower pumps, it is required that you cut with a larger kerf width.  Most systems out there have kerf widths from .030" to .040" (0.76mm to 1.0mm) .  Specialty applications such as jewelry cutting use smaller 0.02" (0.5mm) nozzles.
Q: Can I run multiple nozzles at once?
Yes.  This is a reasonable way to increase productivity without buying a second machine.  You will need a large pump, or several small pumps to operate multiple nozzles at once.  Then, simply mount your nozzles next to each other on the same machine.  There is some risk, however, that a nozzle clog or snag on one nozzle can ruin all the parts underneath the other nozzles.  I personally favor having a couple of smaller machines over a huge machine with many nozzles, but what is right for you will depend on your applications.  Note that when running multiple nozzles, some precision is lost because of the inability to compensate for tool wear exactly over both nozzles, but in most applications it's still possible to get pretty good precision.
Q: Where I live, we are having a drought.  Should I be concerned about water usage?
Yes, but not from your waterjet.  Waterjets use between 1/2 and 2 gallons (1-4 liters or so) of water per minute when cutting.  Some of the water is used for cutting, and some for cooling.  Compare that to how much water it takes to make a pound of beef , and you quickly realize that you can conserve about the same amount of water by simply changing your diet.  If you are still concerned about water consumption then buy an efficient pump that does not use a lot of excess water for cooling, and / or recycle the water.  There are also a host of water recycling options out there.  If you recycle the water, then you may also need a water cooler to prevent the tank water from getting hot and causing thermal expansion in your parts.  Contact the vendor of your pump for more information.
Q: Most of the waterjet machinery that I have seen is huge, expensive, noisy, messy, and low tolerance.  I don't need a giant monster machine in my shop.  Does anyone make a small, clean, quiet, and precise machine, targeted for the job shop / machine shop owner?
YES!  I think this is the most exciting development in the industry:  There is a push towards smaller, more precise, and cheaper machines.  These make great compliments to existing machine shop operations, or additions to existing waterjet shops.  Expect to see a lot of new machines of this type.
I think of it kind of as being analogous to the printing industry:
A few years ago, if you wanted something printed, you went to a specialty shop that had a printing press, and paid an arm and a leg to get your printing work done. In order to get costs down, you printed huge quantities at once.  The setup was tedious, the equipment was big and messy, and it required a lot of special skills.
Now days, in your office, you probably have several printers, and a photocopier.  You might still send some work to the printers, for large volumes, but for the most part you do everything on your easy to use, small, and affordable desktop printer.
This exactly the trend that I see happening with abrasive waterjets.  The trend is towards smaller, cheaper, easier to use and maintain equipment that allow you to make parts "Just In Time".  And like the printing press, there will still be a market for huge machines and high production.
What size machine is best for you?  That depends on your needs.  Keep in mind that sales people will tend to push you into bigger machines, because that is where the money is.   Often "bigger is better", but it can also be simply "bigger is more expensive".  It all depends on your real needs.
Q: I want to build my own waterjet cutting machine.  Is this a good idea, and where do I start?
In general, this is something I strongly recommend against unless either you think building it yourself would be fun, but you don't intend to run it as a business, or there is no machine available on the market that can do the particular highly specialized job that you want to do, and none of the machine builders want to make a custom machine for you (which some will).
Many of the early machines were home built systems consisting of purchased components such as pumps and nozzles married to other components for control and positioning.  But these were prone to a lot of problems that have been addressed in the factory built systems.
Here are some recommendations:
  • Learn what the new machines can do.  Visit several manufacturers and trade shows.  The reason for doing this is so that you understand what you are getting yourself into, and so that you can steal ideas if you still want to continue (watch out for patents, though!).  My bet is that you will opt to buy a manufactured machine instead.  Either way, though, you win by following this advice.
  • Join the [waterjets] discussion group.  There, you can ask questions and discuss ideas with other people who have done this.
  • Use this web site as a resource for finding vendors of spare parts and accessories.
Here are some of the challenges
  • Making the XY positioning system is the easy part.  Just be sure it is very well protected from dust, grit, and moisture, and that the operator of the machine is safely protected.  Use enclosed bellows and non-rusting components wherever you can.  Be wary of simply adapting an old plasma table, because it probably will not have the protection needed.
  • Making your own controller is not easy.  Definitely read the controller section of this web site for a brief overview of the complexity involved, and options in this regard.  I've been involved in making several waterjet controllers, and doing it right is a huge effort, but the differences in ease of use, cutting speed, and part quality are dramatic.  For example, for the same tolerance part, we were able to speed up cutting by well over 200% over traditional non-waterjet specific controllers by optimizing the tool paths based on precision cutting models and such.  Precision and edge quality of the cut were also improved dramatically.  The results are dramatic enough that traditional waterjet operators tend not to believe it until they see it.  This is the main reason why I say that it is not worth making your own waterjet if you intend to operate it for business purposes - you simply won't compete.  That said, if precision and cutting speed and cutting quality are of no concern to you, then there are a zillion controllers out there to choose from. (Though if this is the case, you may also want to consider some other technology for your cutting, such as plasma or torch cutting, etc.)
  • Making your own pump is probably the hardest part.  There are a lot of trade secrets to making a pump that can last more than just a few seconds without being dangerous.  Instead of building your own, at least buy a used pump.  There are quite a few used pumps on the market including factory rebuilt ones available from the pump manufacturers.  There are also used pumps available on the internet, even EBay sometimes, but buyer beware!  The [waterjets] discussion group is a good spot to post a "pump wanted" message.
Final Warning: Don't expect to be competitive with a lot of the manufactured machines out there.  These machines have years of development behind them in terms of software to control and optimize the tool paths, cutting models, and many other features and accessories that make them highly competitive.  If you are doing this as a hobby, then have fun and be careful.  If you are doing this for a business, know what you are getting yourself into.
Q: How much abrasive is used?
Anywhere from zero to about 2 lb. (1 Kg) per minute of cutting.  Obviously waterjets don't use abrasive, so they will cut at zero lb. (0 kg) per minute.  Abrasivejets will run from 0.25 lb. (0.1Kg) per minute to 2.0 lb. (1 Kg) per minute depending on the pump / nozzle you are using.  1 lb. (0.45 kg) per minute is fairly typical.
Q: What does abrasive cost?
Price varies from $0.15 / lb to $0.40 / lb, depending on the quality of the abrasive, and where you buy it.  It is recommended that you pay the extra money for good abrasive, especially if you are new to this technology.  Abrasive is one of the biggest operating costs associated with running the machine.
Consider purchasing abrasive in large quantities for a discount.  You might even coordinate your purchase with your competitor down the street, as you will both save money.
Q: Can you use other abrasives besides Garnet?
Yes.  There are some other abrasive types out there, with various properties that can make your machining cheaper.  For example, if you cut a lot of Aluminum, you can use a softer abrasive than you would use for steel.  The advantage of using a softer abrasive is that you wear your mixing tube (nozzle) out slower.  Garnet is a very good general purpose abrasive, which is why it is so popular.
Warning:   Be careful of, or avoid using abrasives containing silica.  Silicosis, a deadly lung disease, can result from the dust generated!
Q: Why does it matter which abrasive I use, and which is best?
Warning: Do not use silica based abrasives. Silica based abrasives can cause silicosis of the lungs, death, etc.  I.e.. don't try to save money by using sand from the beach!
In general, Garnet is an abrasive that is good for cutting a wide range of materials.  For that reason, it is the most popular.  There are other abrasives that are also popular for those who are cutting a lot of one specific type of material.  For example, if you cut a lot of aluminum, it may be cheaper for you to choose a softer abrasive.  This would allow you to cut the aluminum at perhaps just a slightly slower rate, while saving a lot of wear on your mixing tube, and perhaps also using a cheaper abrasive.
I don't recommend purchasing abrasive on price alone.  Many brands are much more expensive than others.  Often, it is the case that you get what you pay for.  This is because there are many factors that determine a good abrasive.  The advantage of using a high quality abrasive is that you will experience faster cutting, higher precision, and less frequent nozzle plugging.
Here are some qualities to look for in an abrasive that make it "good":
Double sifted:  This means that the abrasive has the fine particles removed, as well as the big particles.  Therefore, you have a consistent mesh size.  Fine particles and large particles both contribute to nozzle plugging, inefficient cutting, and other problems.
Sharp: The sharper the abrasive particle, the better it cuts.  crushed garnet is sharper than garnet from a beach that has been worn into round beads.
Purity:  Look for an abrasive that is pure.  Obviously, if the abrasive is advertised as "garnet", but is full of dirt with only 10% garnet in the mixture, your cutting performance will suffer.  Likewise, if it has unusually hard bits in it, such as aluminum oxide, you may cut marginally faster with a severe drop in nozzle life.
Hardness: The harder the abrasive, the better it will cut.  Of course, for cutting soft materials, you may want to choose a softer abrasive as discussed previously, in order to save money on nozzle wear.
Price: Of course price should be a primary concern.  Just keep in mind that you will sometimes get what you pay for.  Also, understand that a higher priced abrasive may actually reduce your hourly cost of operation.  This is because a good abrasive, that does a good job cutting, will allow you to cut faster.  Thus, you can get more inches of cutting out per dollar spent on abrasive.
If you want maximum cutting speed, then you may want to choose a coarser abrasive, such as 60 mesh or 80 mesh.  If you want smoother surface finish, then choose a finer abrasive such as 100, 120, or 150 mesh.  Consult the manufacturer of your nozzle for recommendations.
When you first get your machine, use the machine with whatever brand of abrasive your equipment manufacturer recommends.  Most likely, they will recommend either their own brand, or one that causes the least trouble.  Later, as you gain experience with the machine, shop around for better deals.
Caution: Be wary of being locked into long term deals on abrasive unless you are absolutely 100% sure that the abrasive you are ordering is right for your long term needs.  I.e. If you think you are getting a good deal by signing a contract for 1 years worth of 80 mesh garnet to cut your 1/8" (3mm) aluminum, at $0.25 / lb, then discover that you could have used a softer or lower grade abrasive at $0.15/lb, then you are out for an entire year using the wrong stuff for the job.
Tip: 80 mesh abrasive is very popular, and in high demand.  Therefore, it is also the most expensive.  If you go with a coarser or finer abrasive, then you can save some money.  The trade-off is that you may not cut as well.  However, in some circumstances, it may be worth it.
Q: Can I save money by recycling abrasive?
Perhaps:
There are two recyclers from WardJet.  According to the manufacturer, the Ward (Water Abrasive Recycling Dispenser) recovers large percentage of used abrasive for re-use.
"The function of the WARD 24 is to remove the sludge from an abrasive waterjet cutting tank, separate out the sludge and all abrasive that is smaller than 100 mesh, then wash the abrasive larger than 100 mesh, dry it and screen it once more, simultaneously allowing operators to add new abrasive to the recycled abrasive at the desired ratio."
- Quote from EasiJet web site
Because I have no personal experience with this product, I can't comment on how good it works.  I would suggest learning more from either the WardJet web site, or maybe discuss it with others at the [waterjets] discussion group.

I don't know of any other place that makes recycling, but if you do, let me know.
Q: What can't an abrasivejet cut?
Not much.  Abrasivejets have some trouble with piercing some materials, and may cause delamination of other materials.  Often, in these cases, it is still possible to cut by reducing pressure, or by pre-drilling start holes, or coming from the edge of the material without piercing.

Tempered glass can not be cut with an abrasivejet. (Although just about any other kind of glass cuts nicely - where I work, we have done a lot of precision cutting of quartz glass, bullet proof glass, and all sorts of other amazing materials).
Q: Can an abrasivejet cut tempered glass?
Not if it is fully tempered.  It must be annealed first, cut, then re-tempered if you want to cut it.  Some people may say that they have cut tempered glass successfully, but they are mistaken, and the glass was not fully tempered.
Q: Would a PC or CNC control be best, and what are the differences between them?
A: This really depends on what it is you are trying to accomplish.  If you are trying to make short runs or just-in-time parts, then the PC is definitely the way to go.  This is because they have very easy to use user interfaces, and are very easy to program.  All you have to do is draw the part, and say "go".  (This is also my personal bias, as I am heavily involved in making PC based controls).
CNC's have the advantage of being able to do highly sophisticated multi-axis work, but are much more difficult to program, even for 2D work, especially in the area of setting speeds and accelerations.  They are not recommended for low volume, just in time, or single part production work  Typically they require a lot of "black art" programming, operator experience, and trial and error.  They are also not efficient at setting feed rates, and require higher horsepower pumps to compensate for poor programming.  This typically means that each part is more expensive than if made on a good PC based controller.  However, CNC may be the only way to go for some kinds of multi-axis work where PC based controllers are simply not available, such as 3D cutting of automotive carpets.
Another advantage of the PC, is it allows you to run the same software on your office PC that you use to control the machine tool.  This allows you to do everything off-line, including training, part simulation, costing, programming, etc.
PC's are also cheaper to buy, cheaper to fix, and cheaper to upgrade.  When you upgrade, you can give your "old" PC to your kids to play with, or use it for off-line programming, etc.
For more details on what is needed in an abrasivejet controller, and an outline of 2 different PC based controllers that I worked on, check out the controller section of this web site.
Q: Why is controller choice so important on an abrasive waterjet?
#1: Because you are cutting with a "floppy tool" that is very picky about feed rates and accelerations.  This is the #1 reason why manufactures are offering PC based controllers.  CNC controllers are just not good at automatically setting feed rates and accelerations.  Some can do it, but not very well.  If the controller does not automatically handle this chore, you have to do it by hand, and you still can't do as good of a job as the PC, due to limitations of CNC controller design.

#2: Because controller technology is changing so rapidly that the software that runs the machine can mean big differences in both precision and speed.  A good controller with a small low cost pump can cut faster and more precise than an average controller with a big expensive pump.  (Much like Mario Andretti in my Honda could get to the grocery store faster than Grandma in a Ferrari.).   So, with that in mind, imagine a great controller connected to a high end pump...
PC based controllers have revolutionized this industry, and changed it from a "black art" to a technology that is easily accessible to any machinist.
For more details check out the controller section of this web site.
Q: What tolerances should the waterjet machinery hold?
A: This depends on what you want to do with the equipment.  Obviously, if you want the most flexibility, you want the most precise machine.  With a precise machine, you will not have to turn down high tolerance work.
The more precise you can make parts, the fewer jobs you have to turn away.  The fewer jobs you turn away, the more parts you will make.  The more parts you make, the more money you make...
Note, however, that precision is much more than machine positioning accuracy.  The controller also plays an important role due to the behaviors of cutting with a "floppy tool".   Please read the Buyers guide , and Controller discussion for more details on this very important point.
Q: What is the speed range a machine needs so that it can handle all materials?
For abrasivejet machining, it is rarely necessary to go over 100 inches per minute (2500 mm/min).  This is because your main limiting factor will be the cutting speed of the abrasive jet cutting process.  You may want the machine to go a little faster than this during traversing, but the traverse speed will play a very minor role compared with the cutting speed.
For water only cutting, you will want to move much faster than this.  If you do primarily water only work, you may want a machine as fast as 300 ipm (7600 mm/min) or faster.  If, like most machine shops, you only do a little water only cutting, I would not worry about maximum speed.
Q: What is the competition?
Competition with conventional machine shops:
Conventional machine shops are already doing a lot of the work that you can do with an abrasivejet.  This is where you have a big advantage.  Many parts are much cheaper and faster to make on an abrasivejet compared with other processes, and therefore, you can make a lot more money.  Also, you can use an abrasivejet to do pre-machining to remove material prior to placing on a Mill, Lathe, or EDM.
Competition with abrasivejet job shops:
This is new technology that has only been embraced by "early innovators" so far.  This means that the market is huge.
I am guessing that there are perhaps 2000-4000(?) abrasivejet installations in operation world wide.  I am not sure of this figure because many of them may be doing stuff like diaper cutting, food processing, high pressure cleaning and paint removal, and other water only and specialty work.  Also, I just don't have access to reliable information in this regard. Basically, there are few abrasivejet systems out there when compared to the demand for this kind of work, but this is changing rapidly.  I have seen studies that suggest the market demand for abrasive waterjets in the US alone is around 50,000 installations.
Q: What size pump would be best?
This depends on the kind of work you want to do.  If you are doing a lot of work in very thick metal, get an efficient pump that is capable of putting a lot of horsepower to the nozzle.  If you are doing a lot of thin metal, or doing water only cutting, get a smaller pump.  Smaller pumps are often cheaper, cost less to run, are easier to maintain, more reliable, and are quieter.  Bigger pumps, however, allow you to cut faster.
Note: It is very important to understand that it is horsepower at the NOZZLE that is important, not the size of the motor turning the pump*.  This is important because many pumps have big motors driving inefficient pumps, while other pumps have smaller motors running efficient pumps.  For example, a 50hp intensifier pump will typically only put 30 hp to the nozzle, while a 30 hp crankshaft pump will put 28 hp to the nozzle. When you look at the price and maintenance differences between the two types of pumps, the lower hp pump quickly starts to look like the better choice:
  • 50 hp Intensifier ~ 30 hp at nozzle ~ 20 hp lost to inefficiencies!
  • 30 hp crankshaft pump ~ 28 hp at nozzle ~ only 2 hp lost!
Please read the Buyers guide for more details on this very important topic.
You may also want to download the abrasivejet feed rate calculator form the software downloads portion of this web site, as it has a feature for computing nozzle horsepower as well as cutting speeds.
* actually, it's a little more complex than just nozzle horsepower.  Nozzle geometry / energy density is also important, but this does not really effect the pumps.
Also, keep in mind that the purpose is usually to make the highest quality part as cheaply as possible.  This does not necessarily translate into making parts as fast as possible by throwing horsepower at the problem.  (Think of the differences between a Top Fuel dragster, and a Kenworth truck.  The dragster is a heck of a lot faster, but the kenworth is a lot more reliable, and is a lot more productive for moving things around.)
Q: What other differences does a different size pump make?
The more power that makes it to the nozzle, the faster you can cut.  The trade off with a higher power pump is cost, efficiency, a larger kerf width, and sometimes a slight loss in precision.  However, you can almost always run a high horsepower pump at lower pressures to reduce the operating cost and maintenance, then run at higher pressures for special jobs that would otherwise try your patience.
Q: Why use multiple heads?
If you are doing lots of the same part over and over, you can produce more at once with multiple heads.  Of course cutting with multiple heads requires that you have more than one pump, or one really big pump.  Also, if something goes wrong with one cutting head, your other parts will also be effected.  Many high production waterjet shops cut with multiple cutting heads, and most job and machine shops use a single head.
Q: What are the relationships among pump horsepower (HP), orifice and nozzle sizes, abrasive types and flow rates, water pressure, cutting speed and quality of cut to edge finish, tolerance and taper?
Myth about pump horsepower: Pump horsepower, in marketing literature, almost always refers to the horsepower of the electric motor that drives the pump, and not the actual horsepower that makes it to the nozzle.  For example, due to inefficiencies, a 50hp Intensifier pump typically puts out 30hp at the nozzle.  Or a 20 hp Crankshaft type pump typically puts 19 hp to the pump.  For this reason, talking about pump horsepower is misleading.  Instead, consider nozzle, or cutting horsepower .
With that understood, we can now talk about the relationship between cutting (nozzle) horsepower, nozzle sizes, abrasive selection, water pressure, etc.
Nozzle Horsepower:  Nozzle horsepower is how much cutting power is at the nozzle.  The more you have the faster you cut. A great way to compute nozzle horsepower, is to use the Feed Rate Calculator, which you can download from this web site .
 

 
Nozzle horsepower is computed from:
  • Pressure
  • Jewel Diameter
So, if you have a .014" jewel, and you have a pressure of 40,000 PSI trying to push water through it, you are cutting with 19 Horsepower!
Or, if you have a 0.015" jewel, and 50,000 PSI, then you are cutting with 30.5 horsepower.

Nozzle sizes:  In basic terms, there are two 3 critical dimensions in a nozzle. (in advanced terms, there is a lot of voo-doo that goes on inside a nozzle that you don't need to worry about.  Leave that up to the manufacturer of the nozzle).  The three critical dimensions are jewel diameter, mixing tube diameter, and mixing tube length.
Jewel (orifice) Diameter: As you can see in the picture, the jewel is where the high pressure exits the plumbing and enters the air in the nozzle.  This jewel is sized so that it maintains pressure behind it, while allowing water to flow at extremely high velocity into the venturi mixing chamber of the nozzle.  The larger the diameter of the hole in the jewel, the more water it flows, and the bigger the pump you need to maintain the same pressure.
Mixing tube diameter:  The inside diameter of the mixing tube determines how fast the mixing tube will wear out, how precise of a cut you can make, and how quickly you can cut.
Properties of a small diameter mixing tube:
- Slightly improved cutting rate
- Slightly decreased nozzle life
- Improved precision
- Smaller kerf width
Properties of a large diameter mixing tube:
- Slightly reduced cutting rate
- Slightly increased nozzle life
- Slight decrease in precision
- Larger "kerf" width
Mixing tube diameter directly relates to kerf width diameter
Mixing tube Length:  Mixing tube length effects the ability of the nozzle to focus.  Typically, longer mixing tubes focus better than shorter ones, due to their longer length.  This will give you slightly more precision due to reduced taper.
Q: Can I recycle worn out mixing tubes, and save a lot of money?
Sometimes.  For example:
You start out enjoying all the benefits of a 0.030" mixing tube.  You cut a little faster, and you have a narrower kerf.
Once the mixing tube is about 75% worn, you have it bored out to 0.040", using an EDM.   Now, your 0.040" tube will not cut quite as fast, or as precisely, but you have extended it's life significantly!  You will have to use an EDM to make the bore, but it can be done.  Note: The nozzle cannot be completely worn out for this to work.
For a company that provides this service (Maxtec), click here :
Another company that does this service is:
JD Tool & Engineering, Inc.
P.O. Box 403
705 Old Hwy 9
Clinton, AR  72031
PH:   501-745-4780
FAX:  501-745-6127
email: jdtool@jdtoolonline.com
If you have a company that also provides this service, please let me know , and I'll list you also.
Is this really practical?  I am not sure.  I have heard opinions in both directions, but I consider it at least worth trying.  (I personally don't recycle - but that is mostly a function of the environment where I am in, where from my point of view the mixing tubes are free, and we nearly always let them wear to 100% for the sake of research.)
Q: What about the waste product? Is it safe, and how is it disposed of?
The waste products are Abrasive, cut material, and dirty water.
Typically solid waste product is Garnet abrasive, mixed small amounts of whatever you have been machining.  It can usually be disposed of in land fill.  If you are machining large amounts of toxic materials such as lead, then you may have to dispose of it as hazardous material.
The water is typically treated as "Gray water" which can be recycled, or sent directly to the sewer.  Again, if you are cutting something toxic, you may need to filter water, and recycle or dispose of it in special circumstances.
Q: How important is software, and can I use my existing (CAD/CAM) program to program an abrasivejet?
Software is extremely important.  You should look at your programming options thoroughly before purchasing a system.  Make sure that you like the included software, and also make sure that you have other programming options available.  (i.e. can you import files from AutoCAD, MasterCAM, Adobe Illustrator, and other popular CAD / CAM / Drawing packages?).
Watch out for proprietary software with "secret", unpublished file formats to store your CAD data, or tool path files.  If you decide later on that you don't like the software that comes with the system, it is very nice to be able to have a post processor written to allow you to use a different CAD package.  That is, if the file format that drives your machine is published.  You may also want to use some other third party software for Nesting, gear generation, or other special shape generation.  In this case, you definitely will want to be able to create the necessary files.
Also watch out for software that you must pay lots of money to upgrade, or pay money for extra seats.  Often, it is to your advantage to run the software on several computers.  Perhaps one seat on the machine, one or two in the office, and another seat at home, or on your laptop.  It is of course also to your advantage to run recent software with all the latest features and bug fixes.
!Beware of large maintenance and upgrade fees.  These hidden costs can be very large, and upgrading software is something you will want to do at least once per year because of the rapid developments in this area, and for simple bug fixes.
Can I "Nest" parts together, and fit a whole bunch to a sheet of material to minimize material wastage?
Yes:  There are many software companies that make "Nesting" software, and some controllers have basic nesting features built right in.  Depending on the kind of production environment your shop is like, you may or may not have any need for nesting software.  For most applications where you are simply cutting the same part over and over, you can simply "step and repeat", or manually nest your parts.  
Nesting software ranges from very simple to extremely complex and capable.  Some packages will even manage your plate inventory for you. Although each nesting software package does basically the same thing (fitting various shaped parts to a plate of material), they all go about it in very unique ways, and each has their advantages and disadvantages.  
Because of the very high price of nesting software $1000.00 to $30,000.00, I recommend that you gain experience with your machine before you commit to purchasing such software.  In most cases, I think you will find that it is not needed, and in other cases you will make a better decision about what kind of nesting software you need, once you understand the machine better.
Again, beware of large maintenance and upgrade fees, but keep in mind also that nesting software companies have to make their money somehow to stay in business.

For more information on software, see the Suppliers Page of this web site.
Can I "scan" parts in using a scanner, digital camera, or other device?
Yes.  Ideally you would start with a CAD file, but if you don't have one then you can use other means to reverse engineer parts or artworks.  There are many "raster to vector" software packages that are used for such purposes.  Note: If you start with very clean black and white / high contrast artworks to begin with, then you will have much better results with this kind of software.  To find such software, search for "Raster to vector conversions" on your favorite search engine.  The two most popular packages are Adobe Streamline from Adobe corporation (though it's kind of out of date now), and the various offerings from Arbor Image Corporation.  Contact the manufacturer of your equipment to see what they recommend.
For more information on software, see the Suppliers Page, and the Controllers Page of this web site.
Q: How important is it to have a good cutting model in the software?
A good cutting model is very important for obtaining precision, and for making good parts without a lot of manual trial and error.
Not only is it important that the model accurately predict jet , behaviors it is also equally important that the controller is capable of somehow translating the cutting model into machine movements that can compensate for the jets . behaviors This is very much akin to a race car:  Not only is it important to have a good driver, it is also important that the car can perform the drivers desired commands.
For more information on this, see the Controller discussion on this web site.
Q: What is Super-Water® and what are it's benefits?
Super-Water® is a chemical that is added to the water of an abrasivejet or waterjet in order to focus the cutting stream, increase cutting speed, and reduce wear of high pressure components.  Traditionally it has been used for high pressure cleaning and  water-only cutting applications.  While I have no personal experience with it, and have no opinion on it to express, it looks like it may offer benefits for abrasivejet cutting applications as well. Click here for more information on Super-Water®.
Q: Is Super-Water® required?
No. It is simply used to improve cutting performance and reduce maintenance.  Most abrasivejet systems do not employ Super-Water®.  I have never seen a system that uses it, so I can't say if it's any good or not.  Let me know what you learn.
Q: Is it possible that my business could grow to require additional system?
Of course!  I have seen many shops purchase second, third, forth, twentieth, etc. machines.  This is just the beginning, and the industry is growing rapidly...
Q: What is the learning curve?
This depends greatly on the equipment you purchase, and what you want to do with it.  Many modern Abrasivejet machine tools are relatively easy to operate, program, and maintain.  Note, that this has not traditionally been the case.  Older generation Abrasivejet machinery was very difficult to program, awkward to maintain, messy to operate, noisy, low precision, etc.  Until about 1995 or so, there was a lot of black art involved.  This is no longer the case.  If you shop around, you will quickly learn that some machines are much easier to use, and more capable than others.
I have seen many people understand and comfortably operate this type of equipment after just 1 day of training.  Others may take up to a week.  But, once again, this is highly dependent on the equipment purchased.  If you buy a lot of accessories, expect to require more training as well.
Of course, there will be the occasional things that confuse and frustrate you.  Your first pump rebuild will probably not be that much fun, but once you learn it, it will be much easier the next time.  If you have trouble, don't forget to call Technical Support, and have them hold your hand.
Tip: Start learning before your machine arrives.  Get a copy of the software.  Get the manuals and other training materials.  read, and play.  If the machine runs under DOS, then learn something about DOS.  If the machine runs under Windows, then start learning Windows.  If it a "G-Code" based machine, then start learning G-Code.  That way, when the factory guy starts to train you, he doesn't have to start by teaching you the alphabet.
Tip 2: Once you have your machine, and are reasonably comfortable with how to use it, schedule follow up training.  When you first get your machine, most of the training will go in one ear, and out the other.  In 3-6 months, get another day or two of training.  Plan for it.
Tip 3: If you are uncomfortable with computers, become comfortable.  Get a computer, take some classes, and have fun.  Good computer skills can go a long way in many areas of abrasive / waterjet machining, and life in general.  They are also very handy for business, email, or just plain fun.
Side Note: Remember: the only reason why 12 year old children pick up computers so fast is because they are not afraid.  Don't be afraid just because you're an adult - the rewards are well worth the effort, and  becoming more so every second.  Abrasive jet machining aside, NOW is the time to gain computer literacy.  It is becoming such a fact of life that shortly those who are not computer literate will be in the same camp as those who are unable to read or write.  If you don't own a computer, then buy one.  I recommend buying from Dell (http://www.dell.com) because they will not rip you off, they offer great service, and they make the highest quality computer that I have ever seen. They are a bit on the expensive side, though, but I think worth the extra money.  I have owned and worked with many brands of computers, and I can say with great confidence that Dell is the best.  If you do buy from dell, buy as a business, and not a home user (This is very important).  My experience with them says that buying as a business will insure that you get better service. Then, buy "Windows XP for dummies", and take a few classes.  Have fun.  Buy some video games (I recommend Half Life 2, Far Cry, or Battlefield 2, and World of Warcraft if you have a hot enough computer to run it.  Otherwise, try Return To Castle Wolfenstein, Half Life (original version), and Star-Wars Jedi Knights II, or Battlefield 1942). Installing games is a good way to learn how to do things on a computer, and you are rewarded with fun. My favorite game related web site is GameSpot. If you need help, then send me an email.
future....
  • Throughout the machine tool world and other industri
    Q: How important is Pressure: Is maximum pressure always better?
    Generally speaking, the higher the pressure of the water, the faster the speed of cutting.  However, pressure is only one of many factors to consider. Among them are:  
    • Operating cost
    • Maintenance
    • Fatigue limits of all high pressure components
    • Cutting speed
    Operating cost is often much lower for lower power machines.  This is simply because lower pressures and lower water flow rates translate directly into longer life of every component that touches the water.  It also translates into fewer consumables, because machines that run at lower pressure wear mixing tubes and jewels slower, and typically consume less garnet.

    Fatigue: At pressures of 60,000 PSI and higher, metal fatigue becomes a serious issue on many components.  Although pumps that can reach 100,000 PSI have been around for many years, nobody runs them at such pressures because of the extreme maintenance issues involved.  For this reason, most manufacturers purposely limit their pumps to below 60,000 PSI.

    Cutting speed     boils down to how much cutting power is exiting the nozzle.  This is determined not only by pressure, but also by the size of the hole you are sending the water through (jewel size).
    To illustrate this concept, have a look at a few nozzle combinations, at various pressures:
     

    30,000 PSI
    40,000 PSI
    50,000 PSI
    100,000 PSI
    0.010" Jewel
    5.84 HP
    8.99 HP
    12.56 HP
    35.52 HP
    0.012" Jewel
    8.40 HP
    12.94 HP
    18.08 HP
    51.15 HP
    0.014" Jewel
    11.44 HP
    17.61 HP
    24.61 HP
    69.62 HP
    0.016" Jewel
    14.94 HP
    23.0 HP
    32.15 HP
    90.93 HP

    As the above chart shows, even at 100,000 PSI, you are still cutting at 35.52 horsepower, if you run a 0.010" jewel.  Compare that to a system pumping 50,000 PSI through a 0.016" jewel, which even at half the pressure, is still cutting at nearly the same rate.
    Of course, few people really run at 100,000 PSI, because that puts an extreme amount of wear on all the high pressure components!  Nevertheless, it is an important illustration that pressure by itself is not very meaningful.
    To make the example even more extreme, consider the case of 1,000,000 PSI behind a jewel that does not have a hole in the middle.  In this case, you have a lot of pressure, but no water coming out at all!  How can that cut?  It doesn't!
    As a general rule of thumb, it is horsepower at the nozzle (cutting horsepower), not the power of the motor turning the pump (pump horsepower), or pressure that determines how quickly a given system can cut!
    This is a generalization, though.  The best way to answer questions about how the various factors effect cutting speed, is to use the Waterjet Web Reference Feed Rate Calculator.  Click here for info or to download Win 95 / 98 / NT 4.0 / 2000 Abrasivejet feed rate calculator software.  This will answer many questions regarding cutting speed in a variety of materials, pressures, nozzle, and pump configurations.
    Q: Why don't you see real-life systems higher than 60,000 PSI?
    Because of metal fatigue.  There have been many pumps developed that can put out pressures higher than 60,000 PSI, but it is not practical to run them at beyond that except for maybe in the testing laboratory.  All the high pressure fittings, plumbing, etc., fatigue and fail quickly at higher pressures.  Because of this, most  manufacturers of pumps purposefully limit them to under 60,000 PSI to prevent their customers from being frustrated and loosing money.
    Q: I don't own a waterjet, but I need to get some work done.  Where do I go?
    Q: What can I do to make my waterjet as maintenance free as possible?
    Waterjets do require periodic maintenance.  Perhaps a little more maintenance than you are used to.  Compared to other machines, you don't do nearly as much "per part" maintenance, but you do do a lot more "weekly maintenance".  For example, you don't need to worry about replacing bits that wear out every few parts, but you do need to replace mixing tubes and jewels after 50 or so hours of cutting.  Anyway here are some tips to minimize your maintenance:
    1. Start with clean water:
      1. If your water has particles in it, or dissolved minerals, these will bang into or accumulate on high pressure components and accelerate wear.  Dissolved minerals can accumulate as a deposit on the top of the jewel, and cause the jet to cut less efficiently, and worse yet, deflect it sideways so it's cutting the side of your mixing tube.  Tiny invisible-to-the-naked-eye sized particles underneath the jewel can cause it to miss align, and eat your mixing tube quickly.  Dirt in the high pressure plumbing can become bullets that crack the jewel.  Etc. etc. 
    2. Be clean. Tiny bits of dirt can have devastating effects on component life - especially the nozzle components.  This is more important than you may think.  When I see people who rebuild or store their spare parts in the dirt, I also see that they complain of low component life and other headaches.
      1. Always rebuild high pressure or nozzle components in the cleanest possible conditions.
      2. Do not store high pressure or nozzle components where dust (or worse yet microscopic abrasive particles) can settle on them.
      3. Rinse all dirt from components prior to disassembly, and go to another room to do maintenance.
      4. Get an ultrasonic cleaner for cleaning nozzle components
      5. When rebuilding something up-stream of the nozzle, remove the nozzle, and flush the lines with low pressure prior to putting the nozzle back on.  This prevents dirt in the lines from damaging the nozzle.
      6. Remember, anything you do upstream has only one way to exit - through the nozzle.
      7. Plungers and seals inside of the pump are also sensitive to particles.
    3. Avoid pressure cycles on high pressure components:  Each time high pressure is applied to the plumbing, the metal expands.  When the pressure is removed, it contracts.  This causes fatigue that can cause the components to eventually crack.  Operating at lower pressures is one for-sure way to solve this.  Pressure fluctuations typically either come from the pump itself, or from turning the nozzle on and off. There are also methods employed in most equipment for maintaining relatively consistent pressure in the high pressure tubing even though the nozzle is being turned on and off.  Understand, though, that all of the high pressure plumbing is considered "wear parts" and does need to be periodically replaced.
    4. Rotate your mixing tube every morning.  In the event that the jewel is slightly miss aligned, it will hit one side of the mixing tube harder than another side.  This causes uneven wear.  By rotating the mixing tube once in a while, this is minimized.
    5. Understand the basic principals of how ultra-high pressure tube fittings work.  They do not work on the same principals as your household plumbing!  For example, the thread is not what makes the seal.  Instead the screw threads force the parts to gether to make a metal-to-metal seal.  The threads are only used to hold the pieces in place.  Once in place, the cone of the tubing fits inside a negative cone in the mating piece. 
      1. There is no need to over-tighten the components.   You do have to make it tight enough to allow it to have a basic metal to metal seal, but you don't have to use your big muscles to do it. 
      2. A small piece of dirt between the cones can scratch it, or otherwise prevent the seal from occurring.  (Therefore, BE CLEAN!)
      3. If you find that you do need to put a lot of torque on the fittings to make a seal, then consider that something is wrong, such as a scratch, bend, or piece of dirt interfering with the seal.  Another possibility is that the cones are not properly touching due to improper assembly of the high pressure seal.  (I'll probably have more on this topic here some day, once I get some pictures.)
      4. If you have a leak, fix it soon.  Otherwise, the leak will erode the components that make the seal, and you will have to replace it.  
      5. If you are at all unsure of what I am talking about here, ask the manufacturer of your equipment to explain it better, because it's important.
    One final note is that when you first get your machine, you will probably be overwhelmed during the few days of training that you get.  Once training is complete, you will feel pretty confident that you know how to operate the machine, and you may have a general idea of how to maintain it.  However, it may be a few weeks before you perform your first maintenance, and even longer before it's time to rebuild the pump.  Once these items do come up, you probably will have forgotten everything you have been taught.  Therefore, consider having someone from the factory or a distributor use your first pump rebuild as an opportunity to provide you with advanced training on the machine operation, and refresher training on how to do maintenance.
    Q: Where can I find waterjets for sale?
    Whether you are looking for used waterjets for sale, or new waterjets for sale, I would suggest that you join the Waterjet Web Reference e-group discussion.  To do so, click here.   This is also a great place to sell your used equipment.

    Or, follow this link for a list of     manufacturers of waterjet equipment.
    Also, search for "waterjet manufacturers" using your favorite search engine.  Last I counted, there were more than 60 of them.
    Q: What does the future of abrasive waterjet machining look like?
    Caution: You are about to read pure speculation, and probably BS! When the walk-man first came out, I thought it would be a total failure because it was so ugly that nobody would be caught dead wearing one.  So, what's the future hold?  As far as I can tell, God has not inspired me to prophecy, so I will only guess.  Also, I have to be careful about giving away sensitive knowledge about where I work (OMAX), so I'm not going to tell you everything.  Anyway, here are some of my guesses:
    Between now and the year 2015:
    • We will see an increase in the total number of manufacturers making these machines. Most of them will be system integrators who buy existing components and assemble them in unique ways.  Others will spawn from job shops that have abrasivejet equipment, but think they can make it better.  (This is pretty much where we are right now.)
    • We will see more and more machines out there in many different shops.  Most of these shops at this moment do not think they have a need for such machines because they don't yet understand what they are really capable of. 
    • Engineers who have been using these machines in College will graduate knowing how to best design parts to take advantages of these machines.  (Many big engineering universities now have at least one waterjet.  Some of them have several.  I think MIT has 5 or 6, for example.)
    • We will see many improvements in terms of maintenance on the machines, and overall quality. 
    • We will see some incremental improvements in precision and speed
    • We will see a lot of refinements and "polish" in the machines, making them more user friendly, nicer looking, easier to work on, etc.
    • We will see a shift from older Intensifier pump designs to more efficient and faster cutting direct drive pumps.  I would guess that nearly all manufacturers by 2015 will have direct drive pumps.  Intensifier pumps will probably still be used on some older machines, or for specialty applications.
    • We will see a few announcements of "revolutionary" technology that will turn out being marketing fluff.
    • We will see perhaps some real revolutionary technology as well, but I don't know what.  Or at least I won't say.
    • Somebody will make an absolute fortune by introducing a cheap, long-life mixing tube.
    Before the year 2030:
    • There will be small size waterjet machine tools in nearly every shop that has a vertical machining center, or a lathe.
    • There will be even more huge machines used for high production
    • I think of the waterjet industry as being about the same place the automotive industry was in the 1920's.  There are a lot of companies that are making a lot of strange contraptions, but as time goes on we will see a more "standard" look to the machines as all the manufacturers borrow the good ideas from their competitors.
    • Of course, there will always be a lot of custom machines as well for custom applications.
    • The total number of waterjet manufacturers will decrease as companies merge.  A few of the others will appear and disappear.  A few will be very successful.
 
  
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