Waterjet Glossary

This page contains information from before 2010. It is left here for archival reasons only.  Although in most cases, the information here should still be relevant and useful, please be aware that the information contained on this page may be out of date.  For the most up to date information please navigate back to the home page.
Abrasive Dynamic Pierce IGES File Orifice Tail
Abrasive Flow Rate DXF File Intensifier Offset Taper
Abrasivejet DWG File Jewel Pierce  
Attenuator EDM Jet Lag PWJ (Pure Water Jet) Tool Offset
AWJ E-Stop Kerf Quality Traverse
Blow-out Etch Kick back Reverse Osmosis Triplex pump
Bridge / Bridging Feed Rate KSI Scribe Ultra High Pressure
CAD (and CAD / CAM) Fixturing Lead-in/lead-out Silicosis UHP
Catch Tank Focusing tube Lag Slat Waterjet
CNC Frosting Machineability Soft Limit Waterjet Brick
Common Line Cutting Garnet Mesh Splash back Weep hole
Crankshaft Pump G-Code Mixing Tube Stand-off Wiggle pierce
Cutting index Hard Limit Muff Stationary Pierce Witness marks
Cutting Quality Hard Water Nesting software SUPER-WATER® WJTA
Cutting Model Hazing Nozzle Striation marks  
Draft Angle Home ORD File Tab / Tabbing  

Abrasive

The cutting medium of an abrasivejet. Usually garnet or similar. See Waterjet abrasives for more information.

Abrasive Flow Rate

The rate at which abrasive flows into the cutting head. Typically, abrasive is added to the nozzle a rates up to one pound (0.5 kg) per minute. You can see the effect of different flow rates on cutting performance using the Waterjet Web Reference Calculator .

Abrasivejet

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

diagram of a generic abrasivejet

(Graphic courtesy of OMAX Corporation)

Other terms loosely used to mean abrasivejet include:

  • waterjet
  • water jet
  • water-jet
  • water cutter
  • water jetting
  • H2O jet
  • abrasive water jet
  • abrasive flow jet
  • water knife
  • AWJ (Abrasive water jet)
  • UHP (Ultra high pressure) abrasive water jet.

Attenuator

An attenuator is a pressure vessel that maintains output pressure for a constant water flow, compensating for uneven pressure generated by some pumps. The attenuator, also called an accumulator, is used in intensifier pumps.

AWJ

Acronym for Abrasive Water Jet (or abrasivejet).

Blow-out

Undesired erosion in areas of the part, usually at the bottoms of inside corners. Blow-out is typically caused by moving too quickly or too slowly at corners. Moving too slowly can cause the jet to dwell, and erode more material than necessary, while moving too quickly can cause the jet to lag or kick back into the part, eroding it in the wrong spot.

Part made from Plexiglas showing blow-out on corners

Compensating for blow-out is a key feature that distinguishes different control technologies. Poor compensation can lead to slower cutting and poorer quality parts, while good compensation can result in considerably faster cutting with better results. Blow-out compensation can occur by careful control of the cutting speed, by tilting the cutting head, or a combination of both.

Bridge / Bridging

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).

Example of "bridging" parts to be cut on a waterjet

7 parts with “bridges” between them, so that all seven parts can be cut in a single pass, and pulled out of the machine all at once, and then broken apart when ready to use.

See also: Tabbing

CAD (and CAD / CAM)

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

OMAX Layout for Windows: CAD / CAM Software designed specifically for waterjet & abrasive waterjet applications

Catch Tank

A tank of water underneath the cutting head to allow the waterjet stream to disperse, and prevent holes in your floor. Catch tanks are sometimes 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.

CNC

Acronym for Computer Numerical Control. A CNC machine is a computer that is controls the motion of a machining tool by reading G-Code.

Common Line Cutting

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.

Common line waterjet cutting

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

Crankshaft Pump

A type of pump where the pressure is generated by plungers that are driven by a crankshaft. Also often called “direct drive pump.” See Crankshaft vs. intensifier pump.

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

See also Triplex Pump or Intensifier pump.

Cutting index

See Machineability

Cutting Quality

A term used on OMAX, and sometimes other controllers, to indicate how the desired surface finish of the part. A quality of “1” is a rough, high speed cut, and a quality of “5” is a very smooth, highly precise operation. “Quality” was coined by OMAX Corporation, and is becoming the standard for describing surface finish for waterjet machined parts. Note, however, there is no standard definition for what each of the Quality numbers mean. For example, one manufacturer’s  “Quality of 1” is not the same as another’s.

OMAX waterjet cutting qualities

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.

Cutting Model

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

Path previewed showing effects of cutting model on speed.

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.

Draft Angle

The angle caused by Taper.

Dynamic Pierce

A method of piercing a material by slowly moving the jet as water and abrasive begin to flow. See Pierce for other popular methods of piercing

DXF File

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.

DWG File

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.

EDM

Acronym for Electrical Discharge Machining. A slow, but extremely precise method of machining using electrical sparks to remove material in very small increments. See Advantages of waterjets compared with EDM .

E-Stop

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

Etch

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.

Etching with waterjet

An example of etching

See also: Scribe

Feed Rate

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

Fixturing

Securing the material you are working with to the cutting table to prevent it from moving during machining. A general machining term derived from the “fixtures” used to secure material. With waterjets, fixturing is simpler and can consist of solely of weights to keep the material from floating. See Fixturing for making waterjet parts .

Focusing tube

Another name for Mixing Tube.

Frosting

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. Frosting can also occur when the waterjet stream bounces back off the slats.

Frosting caused by water jet durring pierce

Frosting around the holes caused by the pierce process

Garnet

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. See Waterjet abrasives for more information.

G-Code

Although not particularly well suited for precision waterjet machining, G-Code is the most popular programming language used for programming CNC machinery. The figure below shows an example of G-Code.
 

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

Hard Limit

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

“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.

Hazing

Another name for Frosting.

Home

The “home” is a spot on the machine that is defined either in software or hardware as a reference point.

IGES File

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

Intensifier

A type of high-pressure pump that uses hydraulics to make very high pressures. See Crankshaft vs. intensifier pump.

50hp Ingersoll Rand SL-IV intensifier pump. Hydraulic power unit is on the bottom (blue) and Intensifier is on top (silver).

Jewel

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

waterjet jewel next to a penny

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.

Jet Lag

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.”

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.

Kerf

The width of the cutting beam. Typically the kerf width for an abrasivejet ranges from 0.020″ to 0.060″ (0.50 to 1.5 mm), depending on the nozzle. A pure waterjet has a narrower kerf, with 0.005″ to 0.014″ (0.13 to 0.36 mm) being typical. See also tool offset.

Kick back

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 or tilting the cutting head.

KSI

Thousands of pounds per square inch. 1 KSI = 1000 Pounds Per Square Inch (PSI) = 69 bar

Lag

See Jet Lag

Lead-in/lead-out

A lead-in is an area in the tool path that “leads into” the rest of the part or feature. While the waterjet moves through the lead-in, the water pressure is being increased to full pressure and the abrasive is being mixed in. At the end of the lead-in, the waterjet stream is fully cutting, avoiding leaving any witness marks or scarring on the part itself. Similarly, a lead-out occurs at the end of the part or feature where the abrasive is turned off and the water pressure is ramped down.

Machineability

A number used to represent how easy it is for a waterjet to machine a given material. Sometimes referred to as “Cutting Index.”

Mesh

The coarseness of abrasive used, with higher numbers being finer abrasive with smaller particles. Most abrasivejet applications use 80 mesh abrasive, but the finer 120 mesh might be used for special applications.

Mixing Tube

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. This is also where the abrasive mixes with the water.

diagram of a generic abrasivejet

Muff

A sponge or brush around the tip of the nozzle to prevent splash.

waterjet picture

Nesting software

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

Nesting software for waterjet

A list of nesting software vendors.

Nozzle

The nozzle can either refer to the complete nozzle assembly (mixing tube, jewel, and nozzle body) or as a synonym for mixing tube.

ORD File

OMAX Routed Data File. This is a file format used by OMAX software and contains routed tool path information. This is the information that the controller needs in order to machine a part. For details on the standard, contact OMAX.

Orifice

See Jewel

Offset

See Tool Offset

Pierce

Piercing is the process of drilling through the material to be machined. Waterjets make their own start holes by “piercing” the material. There are various methods for piercing as described in Different piercing methods.

PWJ (Pure Water Jet)

See Waterjet

Quality

See Cutting Quality

Reverse Osmosis

A method for filtering water where the water is forced through a membrane leaving behind the impurities. Water quality is important for trouble-free waterjet machining as impurities can damage high-pressure components.

Scribe

Scribing is sometimes used to describe etching using water only, with no abrasive added to the stream.

Silicosis

Silicosis is a lung disease caused by inhalation of crystalline silica dust. The small silica dust particles embed themselves deeply into the lungs where oxygen is exchanged with the blood. As a result, lungs cannot be cleared by coughing. Additional damage can be caused by inflammation leading to scar tissue around the silica particles, further reducing lung capacity.

Silicosis is an irreversible condition with no cure. Treatment consists of treating symptoms and preventing further damage to the lungs. Death is frequently from secondary infection, such as tuberculosis.

Never use abrasives containing silica, such as sand, as these can lead to silicosis.

Slat

Supports used to support the material you are machining. They are typically made from steel or stainless steel and are spaced approximately one inch apart. Slats are considered disposable as they get cut during machining by the waterjet stream exiting the material.

material sitting on slats

Material placed on slats

Slats worn from waterjet cutting

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, or flipped upside down. Eventually the slats will cut in half, at which point they are replaced.

An alternative to slats is to use ceramic balls in the catcher tank. A more popular method for accomplishing this is waterjet brick. Some people have used ball bearings in the catcher tank, but the drawback with this is that the bearings can quickly rust together into a solid mass.

Soft Limit

A soft limit is a limitation on nozzle motion imposed by software as a way of defining an area or boundary of motion that 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

Splash back

Splash back occurs when you don’t cut all the way through the material and the waterjet stream bounces off, or the waterjet ricochets off of a slat. This is very common during piercing, or when nozzles fail. The splashing can be contained by wrapping sponges or other guards around nozzles.

Stand-off

The distance between the end of the nozzle’s mixing tube and the surface of the material is called the “stand-off” and is typically about 0.04″ (1 mm). If the stand-off is too small, then the mixing tube is more likely to get plugged, which requires that machining stop while the tube is cleared. If the stand-off is too large, the waterjet stream will spread too much and cutting efficiency and precision will be lost.

Note that pure waterjetting can use both smaller and larger stand-offs than abrasivejet cutting. See Nozzle distance for more information.

Stationary Pierce

A method of piercing the material where the jet turns on, then remains 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 lets you pierce the material in the minimal amount of space, and is the only option for piercing very small holes. See Different piercing methods for other options.

SUPER-WATER®

SUPER-WATER is a chemical that is added to the water of a waterjet in order to focus the cutting stream, increase cutting speed, and reduce wear of high pressure components. For more information, see About SUPER-WATER .

Striation marks

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

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.

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.

waterjet parts with "tabbing"

Parts held in with “tabs”

See also Bridging

Tail

See Jet Lag

Taper

Taper is the difference between the top profile of the cut verses the bottom profile, and is caused by the interaction of the waterjet stream and the material. Taper is affected by the speed of cutting, the thickness of the material, and the hardness of the material. See All about taper for a full discussion.

 

Tool Offset

The distance that the nozzle moves from the desired tool path to account for the kerf produced by the waterjet.

Traverse

Moving the waterjet nozzle without running water or abrasive. Traversing is used to move the cutting head into position to cut.

Waterjet part shown in CAD with traversing

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.

Triplex pump

A type of pump that uses three plungers driven by a crankshaft to make pressure.

See Crankshaft pump

Ultra High Pressure

A term to describe the extreme pressures that are used in waterjet machining. Typically pressures range from 20,000 PSI (1400 bar) to 100,000 PSI (7,000 bar). Most pumps are limited to pressures below 60,000 PSI (4,000 bar) because of metal fatigue limitations in all areas of high pressure plumbing.

UHP

Acronym for “Ultra High Pressure.”

Waterjet

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

diagram of a waterjet

(Graphic courtesy of OMAX Corporation)

Waterjet is a generic term used to describe equipment that uses a high pressure stream of water for cutting or cleaning purposes. Abrasivejet is a subcategory of waterjet in which abrasive is introduced to accelerate the process. Pure waterjet and water-only cutting are phrases for specifically distinguishing waterjets that do not use abrasive.

In other words: abrasivejet and pure waterjet are kinds of waterjet, and waterjet is a kind of machinery.

It is normal, and common, to use the term waterjet to refer to abrasivejets, though in some cases it can be confusing. On this web site, we’ll use waterjet when referring to topics that cover both pure waterjets and abrasivejets, and use the terms pure waterjet and abrasivejet when discussing topics that are specific to one or the other.

You may also see alternate spellings such as water jet, water-jet, abrasive jet, and abrasive-jet (spaces and dashes between the words), though such spellings are less common within the industry.

Waterjet Brick

A rectangular piece of corrugated plastic used instead of slats to support material. See Waterjet Brick for more information.

See also: Slats

Weep hole

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

A typical abrasivejet nozzle. Yellow arrow points to a 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.

Wiggle pierce

A method of piercing where the jet “wiggles” back and forth to cut through the material. This is much faster than a stationary pierce and sometimes faster than dynamic piercing because it allows the jet to escape and clear out removed material. See Pierce and Different piercing methods.

Witness marks

Marks on the final part that “bear witness” to the tool that created them. This is a general machining term and is not specific to waterjets. Well-made waterjet parts do not show witness marks, although they can be caused by poorly fixtured material that vibrates during machining.

WJTA

WaterJet Technology Association. A good source for technical information on waterjet-related technology. (http://www.wjta.org)