Waterjet Glossary:

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Abrasive

The cutting medium of an abrasivejet.  Usually garnet or similar "sand like" substance.

The rate at which abrasive flows into the cutting head.  Typically, abrasive is added to the nozzle from 0 - 1 lb/minute.  You can see the effect of different flow rates on cutting performance using the Abrasivejet Feed Rate Calculator available for download from this web site. Click here to go to software downloads .

A waterjet with the addition of abrasive .  Used to cut or machine nearly any hard material such as metal, stone, glass, etc.

(Graphic courtesy of OMAX Corporation )

Other terms loosely used to mean 'abrasivejet'

• waterjet
• water jet
• water-jet
• water cutter
  
• water jetting
• h20 jet
• abrasive water jet
• abrasive flow jet
  
• Aquajet (tm?)
• hydrojet (tm?)
• JetMachining®
• water knife (tm?)
• AWJ (Abrasive water jet)
• UHP (Ultra high pressure) abrasive water jet.
• Amazing water cutter thingy that cuts steel and stuff (or "AWCTTCSAS")
  

An attenuator is a pressure vessel that maintains output pressure for a constant water flow, compensating for uneven pressure generated by some pumps. (Also called accumulator).

Acronym for "Abrasive Water Jet" (or abrasivejet )

A stream of "bits" used to control machine movements on OMAX controllers.  Effectively allowing the machine to set independent feed rates at over 2000 points per inch.

When cutting multiple parts that might tip and fall into the tank, it is sometimes useful to "bridge" the parts with a thin piece of metal that connects them together.  Then, once the cutting is finished, the parts are removed from the machine, and the bridges are cut off.  (This is similar to the way parts are held together in plastic for plastic hobby models).



Above: 7 parts with "bridges" between them, so that all 7 parts can be cut in a single pass, and pulled out of the machine all at once, and then broken apart by twisting, wire cutters, or similar when ready to use.

See also: Tabbing

Sometimes used to refer to a 3rd axis on the machine, such as a rotary lathe axis.

Computer Aided Design.  CAD software is the software that you use to make drawings of parts. CAM is Computer Aided Manufacturing.  CAM software is used to make tool paths.  Often CAD and CAM software are included in the same software package for convenience.

Above:  My baby: OMAX Layout for Windows.  CAD / CAM Software designed specifically for waterjet & abrasive waterjet applications.

A tank of water underneath the cutting head to allow the cutting beam to disperse, and prevent holes in your floor.  Often catch tanks are filled with other material to slow the jet down, such as ceramic balls.  The catch tank is also used to accumulate spent abrasive, and drop outs from your parts.

Acronym for "Computer Numerical Control".  In basic terms a CNC machine has a computer that is controlling the motion.  See G-Code .

Common line cutting is used when making multiple parts, so that when one part is cut, a portion of the second part is cut as well.  The advantage is that much time is saved, because one cut can make two parts.  The disadvantage is that it is sometimes difficult to program (depending on the geometry), and generally produces lower precision cuts than cutting the parts separately.

Above: An example tool path for common line cutting of multiple "L" shaped parts. (green lines are traverses.)

A type of pump where the pressure is generated by plungers that are driven by a crankshaft.

Above:  Typical 20/30 horsepower crankshaft driven triplex pump.  You can see 3 high pressure cylinders driven by a single crankshaft.

See also Triplex Pump or Intensifier pump .

Also often called "direct drive pump"

See Machineability

1. Simply the "quality" of cut.  2. A term used on OMAX, and sometimes other controllers to indicate how the machine should cut a given surface of the part.  A quality of "1" being a very rough, high speed cut, and a quality of "5" being a very smooth, highly precise operation.  "Quality" was coined by OMAX Corporation, and is becoming the standard for describing surface finish for abrasivejet machined parts.  Note, however, that different manufacturers of equipment use "Quality" to mean different things.   For example what is "Quality of 1" by one manufacturers definition is not the same as anothers "Quality of 1".

Above: Various "Quality" levels.  On this particular part, each "Finger" took approximately the same time to cut.  As you can see, the Quality of "5", which took the longest time to machine, is also the smoothest.

A model of how the abrasivejet or waterjet will behave when cutting.  Cutting models are used to predict how to slow down and compensate for the effects of cutting with a "floppy tool".

Above: A typical waterjet part previewed in color, where the colors represent the speeds predicted and set by the cutting model, in order to make a high tolerance part in minimal time.

A method of piercing a material by allowing the jet to start moving along the part path.  See Pierce for other popular methods of piercing

Drawing Exchange Format.  This is a kind of graphical file format, defined by AutoDesk, inc., that is designed to be a common platform to exchange CAD drawing files between various CAD software packages.

An Autocad Drawing file.  The official specification for this file format is proprietary to AutoDesk corporation, which makes it difficult for third party vendors to be compatible with it.

Acronym for "Electrical Discharge Machining".  A slow, but extremely precise method of machining using electrical sparks to remove material in very small increments.

Emergency Stop.  Typically a button that you press to stop the machine in the event of an emergency.

To mark the material without cutting all the way through.  This is typically accomplished by reducing pressure, reducing abrasive flow rate or increasing feed rate.



Above: an example of etching.

See also: Scribe

The speed at which the cutting head moves.  See also Cutting Model.

See Mixing Tube .

An effect of stray abrasive particles "frosting" the material you are cutting.  It typically occurs right at the edge of where you have cut, or in a circular pattern around where you pierced the material.



Above: Frosting around the holes caused by the pierce process.

The most popular abrasive used in abrasivejet machining.  It is capable of cutting an extremely wide range of materials, yet is soft enough to give you long life of your mixing tube.

Although not particularly well suited for precision abrasivejet machining, G-Code is the most popular programming language used for programming CNC machinery.  For example:
 

G5 M98 KN250 G90 X-1.2148 Y4.3098 F100 MV25 M108 G4X1.5 G91 Y0.360 F25 G3 I0.00 J-0.360 M109 MV25+1 G90 X-0.1048 Y4.3098 F100 MV25 M108 G4X1.5  X-0.2062 F30 G9 N200 X-0.2017 Y 5.3851 N210 G90 X-0.2017 Y 5.3851 N220 G3 I-1.0128 J 0.0018 X-2.2274 Y 5.3846 N230 X-2.2274 Y 5.3846 N200 X-2.2308 Y 0.6173 N210 G90 X-2.2308 Y 0.6173 N220 G3 I 0.4885 J-0.0005 X-1.7354 Y 0.1283 N230 X-1.7354 Y 0.1283 N200 X-0.6971 Y 0.1288 N210 G90 X-0.6971 Y 0.1288

A hard limit is a stop on the machine that prevents the machine from moving further in a given direction.  Typically these are used to prevent the machine from moving beyond its physical limits.

See Soft Limit

"Hard" water is water with a lot of dissolved minerals in it, typically calcium and magnesium. Because water is an excellent solvent, it dissolves small amounts of minerals as it percolates through rocks and soil. As the mineral content increases, so does the "hardness" of the water. Hard water will tend to leave behind mineral deposits, which require frequent cleaning or replacement of pipes, filters, and jewels. (I suppose that Ice is also hard water, but that's typically not what we are talking about when used in then context of waterjetting.)

See Frosting

A spot on the machine that is defined either in software or hardware as a reference point.
Where your heart is.

A CAD file format for exchanging CAD Drawing data between different CAD software systems.

A type of high pressure pump that uses hydraulics to make very high pressures.

Pictured above: 50hp Ingersol Rand SL-IV intensifier pump.  Hydraulic power unit is on the bottom (blue) and Intensifier is on top (the silver thing).

The orifice in which water exits to form the cutting stream.  Typically jewels are made from sapphire, ruby, or diamond (thus, the name "jewel".)

Above: A "jewel" mounted in a steel insert.  See Abrasivejet for a picture of where the jewel is place in relation with the rest of the nozzle assembly.

As the cutting head moves across the material that it is cutting, the spot where the jet exits the material will lag behind the spot where it entered the material.  This lag is "jet lag".

Pictured above:  The jet, as it moves horizontally, lags at the bottom of the cut.  This is why it is so important to slow the machine down when entering a corner.  Slowing allows the tail to catch up, resulting in a square corner.

The width of the cutting beam.  Typically the kerf width for an abrasivejet ranges from 0.020" to 0.060", depending on the nozzle.  A waterjet has a narrower kerf, with 0.005" to 0.014" being typical.  See also tool offset .

As the machine accelerates out of a corner that it has just cut, the jet will "kick back".  This can cause inside corners to be gouged.  Modern controllers help reduce the effects of this by properly adjusting the speeds and/or tilting the cuttin head.

Thousands of pounds per square inch.  1 KSI = 1000 Pounds Per Square Inch (PSI)

See Jet Lag

A number used to represent how easy it is for the abrasivejet or waterjet to machine a given material.  Sometimes referred to as "Cutting Index"

The coarseness of abrasive used.   For example, 80 mesh abrasive is typical of most abrasivejet applications, but 120 mesh, which is a finer abrasive, might be used for special applications.

Sometimes referred to as "nozzle" or Focusing tube.  This is a tube, made from extremely hard material, that focuses the abrasive and water into a coherent beam for cutting.

A sponge or brush around the tip of the nozzle to prevent splash. (Words like this make you wonder if porn-blocking software will block this web site also?)

Nesting software is used to optimally fit many different parts to a single sheet of material.  

For a list of nesting software vendors, and some advice on buying, click here.

Term used to describe accelerations having to do with the physical limits of the machine, due to Newton's Laws.  (As opposed to acceleration limits due to the cutting effects of the jet, and cutting model.).

Usually, when someone says "nozzle" they are either referring to the complete nozzle assembly (mixing tube + Jewel + nozzle body and perhaps some plumbing.)  Other times, "nozzle" is used as a synonym for Mixing tube.

OMAX Routed Data File.  A file format containing routed tool path information. (I.e. it's a tool path, and not a CAD drawing.).  This is the information that the controller needs in order to machine a part.  For details on the standard, contact OMAX , or download it from their technical support web site.

See Jewel

See Tool Offset

A "Pierce" is the process of drilling through the material to be machined.  Abrasivejets make their own start holes by "piercing" the material.

There are various methods for piercing:

Stationary Piercing (very slow on thick materials, but good for small hole drilling or piercing thin materials.)
Dynamic Piercing (usually faster than stationary, but requires a lot of room on thick materials)
Wiggle Piercing (usually the fastest method of piercing where there is not enough room for dynamic)

PWJ (Pure Water Jet)

See Waterjet

See Cutting Quality

A method for filtering water.

This is a word that is sometimes use to distinguish between etching with abrasive, and scribing with water only.  Similar processes, except etch uses abrasive and scribe does not.  I don't know if this is an industry wide term, but when I was writing the first iteration of the OMAX controller, I needed some way of distinguishing between the two modes of operation.

See also Etch

"Silicosis is a disabling and sometimes fatal lung disease which can afflict workers who are overexposed to fine airborne particles of crystalline silica. Since crystalline silica is the second most common mineral in the earth's crust a basic component of sand, quartz and granite rock more than 1 million workers in many different types of jobs are at-risk of developing silicosis, including highway construction workers, miners, sand-blasters, and foundry workers. When workers breathe in dust containing silica, scar tissue can form in their lungs and reduce their ability to extract oxygen from the air. There is no cure for silicosis -- prevention is the only answer."

- Quote from http://www.cdc.gov/niosh/nmsilcon.html

For the above reason, I would avoid using abrasives containing silica (like sand).  Use at your own risk!

One of the supports used to support the material you are machining.  They are typically disposable.

Above: Material placed on a series of slats. 

An alternate to slats, or a complement to them, is to use ceramic balls.  I have not tried this myself, but it appears to be a good technique, especially for small parts that might otherwise tip or fall in-between slats.  A more popular method for accomplishing this is also waterjet brick.

A common question is, "If the abrasivejet can cut just about anything, then how come the slats don't get cut?"  The answer is that they do:

Above: Slats worn from cutting.

As the jet cuts the parts, it goes right on through, and cuts the support slats.  However, the slats are thin in the horizontal direction, and very thick in the vertical direction.  What happens then, is that the jet gets part way down the slats, and then skips to the side, and does not cut the slat all the way through.  Eventually, the slats wear until they look like a bunch of rusty needles.  At this point, they are rotated to a less frequently used area of the table, and / or flipped upside down.  Finally, the slats will eventually cut in half, at which point they are replaced.

See also: Waterjet Brick

Software limit.  A means of defining an area or boundary of motion for which the machine cannot exceed.  Typically these are used to define the cutting envelope in which the head can move without crashing into something.  This is done in software, instead of hardware, so that it can be changed when you change your fixturing or setup, and so that the machine can warn you ahead of time before you attempt to do an impossible move.

See hard limit

The mess that is made when you don't cut all the way through, or the jet ricochets off of a slat.  Very common during piercing, or when nozzles fail.  This is the reason you often see sponges or other guards wrapped around nozzles.

A method of piercing the material where the jet turns on, then stays stationary until the material is pierced.  This is typically a very slow method of piercing, but is fine for thin materials that pierce quickly no matter what.  It also allows you to pierce the material in the minimal amount of space, and is the only option for piercing very small holes.  See Pierce for other options.

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. Click here for more information on Super-Water®.

The marks left by the jet as it wiggles around.  The faster you cut, the more striation marks form.

Pictured above: A very severe case of striation marks in 7" thick Plexiglas.  In this case, the jet was moving so quickly that it did not cut all the way through.  (Normally you would cut at a slower rate, and get a much better cut, but then I wouldn't have a picture of striations to show you!)

Tab / Tabbing:

Tabbing is a method for holding parts in place, by leaving a small piece of material that is connected to the original plate from which it is being cut, so that they don't fall into the tank or tip and collide with the nozzle after they are done being cut out. 

Above: Parts held in with "tabs".

See also Bridging

See Jet Lag

Taper is the difference between the top profile of the cut verses the bottom profile.
 

Pictured here are 4 common forms of "taper".    At the top is taper caused by cutting quickly ("V" shaped taper.  It is most common in very thin materials).  Under that is zero taper. Below that is reverse taper, usually caused by cutting too slowly. At the bottom is "barrel taper", which can occur in thick materials.

It is also possible to find "combination taper", where two of the above types of taper may combine.

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.
• Thickness of material (thinner materials tend to exhibit more taper than thicker materials)

Because the cutting beam of an Abrasivejet or a waterjet is not infinitely thin, it is necessary to offset the tool slightly from the geometry of the part.  For example, a typical kerf width of a nozzle is about 0.030".  If you were to trace the exact outline of the part you want to cut, the part would be undersized by 0.015", which is half of the kerf width.  Therefore, it is necessary to follow a path that is "offset" by this amount.
   

Left: The original part as drawn in a CAD system (Purple) with the actual path the machine will follow (Yellow), which is offset from the original part.  The blue dot represents the jet.  Notice that by following the yellow path, the purple part will be cut to exact size.  If we were to follow the purple path, the part would come out undersized.

So how do you measure the width of the jet?

Obviously, you can't use a ruler!  What you do, is you cut a part of known dimensions, then measure the error.  For low precision work, you can just guess that it's 1/2 the width of the mixing tube's inside diameter.  For high precision work, it is necessary to measure the error on a previously machined part.

The part pictured above was designed for this specific purpose.  Each "leg" is drawn to be exactly 1" wide.  By measuring the actual dimension of the finished part, you can determine the error in 3 axis of motion X, Y, and combined XY.  By measuring 3 legs, instead of just one, you can also get an idea of the roundness of your jet.

Normal machine movement without cutting, for example to move the cutting head into position to cut.



Above: A typical waterjet part.  Red lines represent areas that will be cut, and the green lines represent traverses, where the cutting head is moved, but not turned on.

A type of pump that uses 3 plungers driven by a crankshaft to make pressure.  See Crankshaft pump .

A term to describe the extreme pressures that are used in waterjet and abrasivejet machining.  Typically pressures range from 20,000 PSI to 100,000 PSI.  Most pumps are limited to pressures below 60,000 KSI due to metal fatigue limitations in all areas of high pressure plumbing.

Acronym for "Ultra High Pressure ".

A pressurized jet of water exiting a small orifice at extreme velocity.  Used to cut soft materials such as foam, rubber, cloth, paper, etc.

(Graphic courtesy of OMAX Corporation )

Sometimes people use the word "waterjet" when they really mean "abrasivejet".  See Abrasivejet

Waterjet Brick

An surface made from corrugated plastic as an alternative to slats.  It is very useful when machining tiny parts that would fall between the slats and get lost.  It is also useful when cutting scratch-prone materials where splash back from the slats might frost the underside of the material.  The primary disadvantage is that waterjet brick wears very quickly, and as it wears, it fills the catch tank with gooey plastic powder.

Above: Slice of a rock held down with wood screws into waterjet brick. Bicycle was machined using a special "mini-jet" nozzle, and cut on top of waterjet brick.  For this kind of work, waterjet brick is almost perfect.

My recommendation is to put waterjet brick in a portion of your tank, and regular slats in other areas.  Or, simply place the brick on top of the slats when needed.  As with slats, it is possible to get some additional life from brick by flipping it upside down once one  side is worn.

See also: Slats

A small hole drilled into high pressure fittings to allow the water to escape in a safe manner should a leak occur.

Pictured above:  A typical abrasivejet nozzle.  Yellow arrow points to weep hole.  Should a leak occur in one of the internal seals, water will escape out this hole.  Because the hole is a large diameter, escaping water will be lower pressure than if it were to escape through a tiny crack.  You will see holes like this on all high pressure fittings and components.

A method of piercing where the jet "wiggles" back and forth to "dig" it's way down.  This is much faster than "stationary" and sometimes faster than "dynamic" piercing because it allows the jet to escape and clear out removed material.  See Pierce

WaterJet Technology Association.  A good source for hard core information on waterjet and abrasivejet related technology. (http://www.wjta.org )