# Abrasive waterjet cutting

Erosive profiling with material-specific piercing, taper, cut-quality, fixturing and finished-feature acceptance requirements.

Reviewed: 2026-11-01

Tags: processes, shaping, waterjet, abrasive-cutting

[Compare cutting routes](../../production/alternative-processes-and-route-tradeoffs.md) before specifying the complete route.

In the worked slot example, **6.00 mm at the top** and **5.70 mm at the bottom** through **20.0 mm plate** give **0.150 mm inward taper per wall**, or **0.430° per wall**, assuming straight symmetric walls. The bottom misses a **5.90 mm minimum throughout** by **0.20 mm**. Check the actual wall profile, local striations and measurement uncertainty.


## Process and intended result

Berkeley's OMAX protocol specifies water and garnet. OMAX's soft-material water-only nozzle omits the abrasive mixing chamber and tube. Specify the cutting route on the order. [Berkeley OMAX protocol, page 2](https://me.berkeley.edu/wp-content/uploads/2025/05/Omax-Abrasive-Jet-Machining-Protocol-2024.pdf), [OMAX nozzle explanation](https://www.omax.com/en/learn/how-does-waterjet-work/)

The result can be a finished profile or a near-net blank requiring subsequent machining. Define the actual material and thickness, contour, functional faces, tolerance and delivered edge condition before choosing the route. The ability to separate stock does not establish precision at every depth, an undamaged pierce region or a ready-to-assemble hole.

## Cold cutting is not a complete surface-integrity claim

Flow describes abrasive waterjet as erosive cutting and promotes the absence of a heat-affected zone in its composite applications. This distinguishes it from a process relying on thermal melting, but does not establish absence of every other defect. Qualify edge damage, internal separation and final cleanliness for the actual material system rather than converting a thermal-process advantage into a universal damage-free claim. [Flow composite applications](https://www.flowwaterjet.com/solutions/applications/composites)

Berkeley's shop experience identifies chipping/cratering around acrylic pierces, underside hazing from back spray, and challenges with laminates or materials affected by water exposure. It describes predrilled starts as one successful approach for certain laminates. Those observations are equipment/material examples, not proof that every laminate requires predrilling or that another setup can never avoid hazing. [Berkeley process limitations, page 2](https://me.berkeley.edu/wp-content/uploads/2025/05/Omax-Abrasive-Jet-Machining-Protocol-2024.pdf)

## Material, piercing and entry strategy

| Material/feature question | What to establish during development |
| --- | --- |
| Brittle stock | Whether piercing, entry and support create cracks or chips |
| Laminates/composites | Layer/bond condition, separation at entry and along the cut, and water compatibility |
| Finished visible faces | Acceptable frosting, hazing, edge damage and which side faces the jet |
| Small holes or narrow slots | Actual through-thickness geometry and any machining allowance |
| Thin or small parts | Support, movement, tabs and retention through final separation |

OMAX's **1 July 2019** glass guidance warns that tempered glass will shatter and should not be machined by this route. For other glass, it identifies piercing as a particularly vulnerable stage and discusses edge entry, suitable support and equipment-specific assisted/low-pressure piercing. Use the installed system's approved method and representative trials; no pressure or nozzle modification from that example is prescribed here. [OMAX cutting glass](https://www.omax.com/en/media-center/tips/cutting-glass-waterjet/)

Place pierces and lead-ins where their damage and witness marks are acceptable. Coordinate entry, exit, tabs and later cleanup with the drawing. A good straight-edge sample does not qualify a brittle internal pierce or a small unsupported island.

## Jet motion, kerf and taper

The jet is not a rigid end mill. OMAX explains that it bends and changes shape through the material; corners and curves require motion compensation. Its accuracy discussion explicitly separates table positioning accuracy from the final part, which also depends on material, thickness, speed and the jet's behavior. Do not use a machine's axis-accuracy number as a blanket part-tolerance guarantee. [OMAX motion and accuracy explanation](https://www.omax.com/en/learn/how-does-waterjet-work/)

OMAX's **6 September 2017** taper article describes different edge shapes, including both taper directions, and notes that taper can differ between lines and arcs even with the same settings. It identifies cutting-speed selection and a particular software compensation feature as tools for reducing taper. These are process controls to qualify, not proof that every programmed contour is square. [OMAX taper compensation](https://www.omax.com/en/media-center/tips/taper-compensation/)

Specify whether size applies at the top, bottom, a defined plane, or throughout the section. Define perpendicularity, angularity or other geometry separately where it matters. Kerf compensation sets the intended path relative to the drawing, while taper and local jet behavior determine how that path develops through thickness. Inspect critical transitions and both faces instead of accepting the top outline alone.

### Original bounded taper example

Assume an ideal straight slot through a **20.0 mm** plate has width **6.00 mm at the top** and **5.70 mm at the bottom**. Assume symmetric, straight slot walls and parallel reference faces. Each wall moves inward by:

`(6.00 − 5.70) / 2 = 0.150 mm`.

The inclination of each wall relative to the thickness direction is:

`angle = arctan(0.150 / 20.0) ≈ 0.430°`.

Inspect at the depths specified on the drawing. Nonstraight walls, asymmetric cuts and local striations require more than a two-width angle calculation.

## Cut quality, consumables and thickness

OMAX's ProtoMAX knowledge base, marked **version 32.8, 17 May 2021**, describes its quality settings as controls on piercing and cutting speed. Higher numbered settings generally move more slowly and produce a smoother edge in that system. It explicitly says surface quality does not correspond to tolerance. “Quality 5” is therefore a controller-specific selection, not a substitute for numerical dimensional, texture or defect requirements. [ProtoMAX quality overview](https://knowledgebase.omax.com/protomax/content/wh-protomax/layout/quality_numbers.htm)

Nozzle condition and setup belong in the qualified route. OMAX identifies wear and maintenance of the cutting head as relevant to precision. Record the installed nozzle/abrasive arrangement and relevant operating controls, then reassess actual results when consumables or material change. A pressure setpoint alone does not describe the full cutting system. [OMAX cutting-head maintenance](https://www.omax.com/en/learn/how-does-waterjet-work/)

OMAX's **6 July 2020** thick-material discussion emphasizes the interaction of hardware, software, material and jet stabilization. Its broad cutting-capacity claims do not establish a universal maximum usable thickness or the same cost, speed and tolerance at every thickness. Qualify the required section and geometry. [OMAX thick-material discussion](https://www.omax.com/en/media-center/tips/waterjet-myths-thick-material/)

## Fixturing, secondary operations and inspection

Berkeley calls for hold-down margin, retention tabs and separate profile/dimensioned files. Agree stock support, retention, file scale and authoritative dimensions with the actual processor. [Berkeley job and toolpath guidance, pages 1–3](https://me.berkeley.edu/wp-content/uploads/2025/05/Omax-Abrasive-Jet-Machining-Protocol-2024.pdf)

Plan reaming, tapping, milling or edge finishing where final features require it. State the machining allowance and verify that both faces and internal walls leave sufficient stock. Clean and dry to the downstream assembly, bonding or coating requirement, and inspect any required edges after the final relevant operation.

A useful release package identifies material/lot and thickness, drawing revision, profile scale, datum/reference faces, significant contours, pierce/lead/tab allowances, through-thickness size and taper requirements, edge/texture limits, secondary machining and acceptance locations. Retain representative trial results for critical material/geometry combinations; a photograph or a passing outside dimension is not complete evidence for the entire part.

The OMAX article dates and ProtoMAX version are printed on their pages as cited. The Berkeley file is labeled 2024 in its filename, but no unambiguous printed technical issue date is assigned here; its 2025 hosting path is not used as an edition date. Flow and the general OMAX technology page are undated technical web descriptions. The taper calculation is original.

## Related reference

[Manufacturing processes](../index.md)