Water-only waterjet cutting

Compare cutting routes before specifying the complete route.

With a trial 0.20 mm kerf, a 50.00 mm disk needs a 50.20 mm jet-center path diameter and a 10.00 mm hole needs a 9.80 mm path. If kerf grows to 0.26 mm at the same paths, the result is a 49.94 mm disk and 10.06 mm hole. Verify taper, jet lag and material compression separately.

KMT's water-only head uses a valve and a sapphire or diamond orifice. An abrasive head adds a downstream mixing arrangement and focusing tube. KMT, Water-only and abrasive cutting-head descriptions, undated

“Pure-water” identifies the absence of added abrasive. Specify water quality, hygiene and prior-media contamination separately where the stock requires it.

Select by the actual stock, not a broad material name

Soft foam, sponge, paper, textiles, gasket materials, and selected rubbers are common candidates. Flow distinguishes pure-water cutting of soft materials from abrasive cutting of hard materials in its process overview. A waterjet system's general ability to cut metal or glass is not evidence that it can do so in water-only mode. Flow, Waterjet Cutting Technology overview, undated

OMAX specifically identifies foam rubber and softer rubber as water-only applications, while assigning fiber-reinforced or very hard rubber to abrasive waterjet cutting. Its plastics examples also distinguish abrasive cutting of polycarbonate. Do not transfer a soft-rubber demonstration to a reinforced gasket solely because both products are called rubber. OMAX, What materials can waterjets cut?, undated

Provide the supplier with grade, thickness, density or cellular structure where relevant, reinforcement, backing layers, adhesives, surface condition, and functional requirements. Trial the complete stack when laminates or multiple sheets are involved. Define whether water absorption, wetting, edge damage, layer separation, or drying is acceptable. These are application questions to resolve, not performance guarantees inferred from a list of cuttable materials.

Flow's foam page describes low cutting forces, narrow kerfs, and material-thickness-dependent single-pass capability. Its “cold cutting” description concerns avoiding the thermal cutting effects associated with other routes; it does not establish zero deformation, zero water exposure, or zero workholding requirements for every foam. Flow, Cutting Foam with Waterjet, undated

Match the head and machine configuration

Confirm installed pump/head compatibility, rated pressure, orifice and valve configuration, standoff, motion control, support/catcher arrangement, and approved conversion procedure. Stopping the abrasive feed does not necessarily reproduce the coherent jet or geometry of a dedicated pure-water head.

OMAX's GlobalMAX Water Only help recommends a dedicated nozzle. It explains that an abrasive nozzle places the orifice farther from the material and can introduce air through the abrasive line, disturbing the jet. Those observations describe that arrangement, not authorization to modify another head's feed ports. OMAX GlobalMAX, Water Only, undated software help

As a dated equipment example, Finepart's Options for Finecut WMC500II, printed Version 20180217, ©2006–2018, lists pure-water kit 6 001 200 with its own nozzle tube and holder, replacing the abrasive cutting arrangement. This establishes a specific available configuration in that edition, not current compatibility with every Finepart machine. The PDF's 2022 upload directory is not its edition date. Finepart options catalogue, pure-water option

KMT's AQUALINE sheet carries the printed footer 01/2022 and distinguishes normally open and normally closed valve behavior. Head actuation and pressure release must follow the selected assembly's instructions; do not assume that loss of control air produces the same state on all heads. KMT AQUALINE water-only nozzle sheet

Define kerf, path, and piercing behavior

The effective kerf is the cut width in the actual stock under the selected conditions. It need not equal the jewel-orifice diameter. Check entry and exit geometry, taper, local features, and the measurement condition of soft stock rather than accepting a nozzle dimension as the part tolerance.

GlobalMAX's help states that Water Only applies a path offset, while Scribe and the water-only Slit variant do not apply that kerf compensation. It also calls for lead-ins and lead-outs for the compensated route. These names and behaviors are specific to the documented software; verify the installed controller's equivalent settings. OMAX GlobalMAX, Water Only path behavior

Its separate recompilation help says that the specified water-only feed is constant and is not adjusted for part geometry. Therefore, selecting that mode does not automatically establish appropriate corner behavior or detailed-feature quality. Qualify pressure, speed, pierce strategy, and transitions on representative material rather than borrowing abrasive-cut quality settings. OMAX GlobalMAX, To Recompile a Part

Worked example: offset versus measured kerf

This original geometric example assumes a flat, stable sheet and an effective kerf of 0.20 mm, established by a representative trial. Ignore taper, jet lag, compression, and corner effects for this calculation.

• For a 50.00 mm external disk, the jet-center path diameter is 50.00 + 0.20 = 50.20 mm.
• For a 10.00 mm internal hole, the path diameter is 10.00 − 0.20 = 9.80 mm.
• If actual kerf becomes 0.26 mm while those paths remain unchanged, disk diameter becomes 50.20 − 0.26 = 49.94 mm, and hole diameter becomes 9.80 + 0.26 = 10.06 mm.

The radius offset is half the kerf, but the diameter error equals the full kerf change. The calculation illustrates compensation direction; it is not a claim of achievable tolerance or a recommendation to use this kerf on any machine.

Support, water condition, and inspection

Support the stock so it does not shift, sag, compress excessively, or move when the final connecting material is cut. Plan the cut sequence, lead locations, small-part retention, and access to the catcher. Check the relaxed part after release from the support. If a stack is proposed, verify alignment and quality through the entire stack rather than assuming identical output on every layer.

Water-only operation still requires the pump's specified inlet water and maintenance. OMAX's April 12, 2022 water-quality article concerns its abrasive systems, but the relevant lesson for a shared high-pressure supply is to test inlet water and monitor it over time. Its numerical treatment recommendations should not be transferred as universal pure-water specifications. OMAX, Maintain Water Quality and Temperature for Waterjet Machine Longevity

For a specific maintenance mechanism, OMAX's ProtoMAX instruction DocRev 401440C-EN describes mineral deposits, clogging, wear, or misalignment affecting jewel-orifice jet quality. That is model-specific maintenance guidance, not a pure-water-head disassembly procedure. Use the installed head's cleaning, depressurization, replacement, and guarding instructions. OMAX, Clean the Orifice and Nozzle Body

Agree on dimensions and measurement force, free-state shape, edge tearing or roughness, taper, complete separation, retained moisture, and downstream cleanliness. Food, medical, sealing, or adhesive-bonding applications require their own equipment and cleanliness qualification; absence of garnet does not establish suitability.

A useful handoff includes drawing revision, complete material construction, thickness, delivery condition, confirmed water-only configuration, trial results, kerf/offset basis, support and sequence plan, and finished-part acceptance. Separate machine positioning capability from demonstrated cut-part capability.

Related reference

Manufacturing processes