Jet Stream Manufacturing: Waterjet Cutting Services
  Jet Stream Mfg Jet Stream Building

125 S. Front St.
Colwyn, PA 19023

  Custom manufacturing and abrasive waterjet cutting services since 1991.
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Technical Information:



Here is some information that can help anyone interested in learning about water jet cutting. Although water jet machines use many of the same principles as conventional machine shop tools such as lathes and milling machines, the details of the processes are quite different. This includes tolerances, surface finish, size of table, and expendable materials. As with any process, there are advantages and disadvantages. Look over the list below and see if water jet cutting can reduce your cost or do a job not possible any other way.

  1. SIZE LIMITATIONS: Water jet machines have large tables for cutting sheets of material up to 6x8 feet. Larger sheets may be accommodated by cutting half the sheet at a time. Small parts may be cut down to about 1/4 to 1/8 inch depending on the material.

  2. TOLERANCES: Water jet machines can cut within +/- 0.020 accuracy. On small pieces with special care, accuracies of +/- 0.002 can be held. The accuracies apply to the top of the material. If the material is thick, the side is tapered so that the top is smaller than the bottom. This is caused by a reduction in cutting power of the jet stream as it passes down through the material. The amount of taper is effected by the feed rate of the machine. Ideal taper speed can be as slow as 15-20% of maximum straight cut speeds. Normal taper is about 0.005-0.010 on each side.

  3. REPEATABILITY: The repeatability of machines is on the order of +/- 0.002 in most cases. There is some variation due to the flow rate of the abrasive delivery to the head. Backlash in the positioning system also causes some error.

  4. FINISH: The cut edge finish appears similar to a sand blasted surface. Normal abrasive is 80 grit size. Jobs can be run with 120 grit for a better finish at higher cost.

  5. ROOSTER TAIL: (Jet Lag) As the cutting speed is increased, the bottom of the cut lags the top of the cut. This is more prominant in thicker parts and is called Rooster Tailing or Jet Lag. Rooster Tailing also leads to under cutting at inside corners as well as a tang at outside corners. The effect only occurs on the bottom side of the material with the top side appearing perfect. In addition, if the jet crosses or nears another previously cut line or the edge of the material, then the jet may jump prematurely into the hole and leave a small tang of uncut material behind as the jet moves on.

  6. ROOSTER TAIL REMOVAL: The effects of rooster tailing are reduced by setting the machine's computer controls to automatically slow down at curves and corners. Since the effect is prominent only at curves and corners, the cutting speed can be set higher for straight cuts. It is often difficult or impossible to remove all effects of rooster tailing this way, since the width of the cut changes as the speed is decreased.

  7. NESTING: Parts can be closely nested on a sheet to save material. Since the kerf or width of cut is only 0.04 inch, odd shaped parts can greatly benefit from nesting. A set of parts of different shapes but the same thickness can easily be nested and cut using the same program.

  8. TOOL SIZE (KERF): In materials that can be cut with water only and no abrasive, including some rubber and vinyl flooring, the kerf (tool size) is about 0.006 inch which allows cutting of very fine details. Individual pieces may be as small as 1/8 inch with even smaller edge details. In materials requiring abrasive, the kerf is about 0.040 inch. Tool size only effects inside corners of angle less then 180 degrees which will be rounded to the radius of the tool. Outside corners of angle greater than 180 degrees can be cut square without much rounding.

  9. SPEED: The cutting speed is important to both customer and shop, because it strongly affects the cost of the job and the quality of the cut (roughness, taper,  ). When there is a large variance in bid prices, it could be due to the low bidder quoting a fast cutting speed which will produce a poor quality edge. The quality of the edge should always be specified on quotations to obtain meaningful prices.

  10. MATERIALS: The water jet process will cut any material softer than the garnet abrasive mixed into the water stream. All metals, plastics, composites, tile, marble, and granite can be cut. Thickness is limited only by the machine size. For some materials at certain thicknesses, other methods of cutting are less expensive. Choices of methods are in many cases obscured by other advantages such as superior finish, no hardening of the metal, no warping or distortion, small kerf, and ability to cut brittle material such as glass and stone without chipping.

  11. SECONDARY OPERATIONS: In many cases, secondary finishing can be eliminated. In the case of marble, granite, and slate finished pieces cut to intricate shapes fit together without further effort to form artistic patterns for floor and wall use. With machine parts, intricate parts with slots, holes, and contours can be made to close tolerances and used as is or with minimum secondary operations such as counter boring, and bending.

  12. TOOLING: Conventional machine tools require fixtures to keep the work from moving and deflecting under the pressure of the tool. The water jet process exerts no such pressure and therefore does not need positioning and clamping devices. A sheet of material can be placed on the table and parts may be cut from it without clamps. Small pieces may need to be held or positioned for cutting using simple stops on the table surface.

  13. SMALL PARTS: Small parts can be cut and retained in the master plate by tabbing. With tabbing, the start and stop point of the cutting program leaves the part attached by a small bridge. The tab width is controlled so that it will support the part but can easily be broken and ground off. The tab is similar to the sprue in a plastic molded part.

    ideal (3-5") - good gap and line width are easiest to cut.
    large (6"+) - smoothness problems arise due to enlargement, requiring additional design time.
    small (1-2") - small gap and line width problems are hard to cut and limit the material selection.
    very small (less than 1") - capital letters as small as 3/8 are possible with water only for simple fonts in soft, non-brittle materials like leather or rubber.


Water Jet competes favorably with

  • Extreme accuracy is not required.
  • Parts are not conductive.
  • Burned edge is unacceptable.
  • Additional machining is required.
  • Low cost is important.

Water Jet competes favorably with

  • Material is over 1/4 inch thick.
  • Parts are SS or exotic material.
  • Parts are copper or brass.
  • Parts are shiny.
  • Burned edge is unacceptable.
  • Distortion is unacceptable.
  • Additional machining is required.

Water Jet competes favorably with

  • Burned edge is unacceptable.
  • Distortion is unacceptable.
  • Intricate shape required.
  • Nesting yield is important.
  • Good edge finish is important.
  • Closer tolerance is required.
  • Additional machining or finishing is required.

Water Jet competes favorably with

  • Cutting large parts.
  • Extreme accuracy not required.
  • Part is used as cut.
  • Nesting yield is important.
  • Intricate shape is required.
  • Parts are hard on tools.
  • Parts are brittle, hard, soft.
  • Run length is intermediate.
  • Tooling is expensive.
  • Frequent design changes are expected.