Garnet abrasive for waterjet cutting
GRM Garnet is crushed hard-rock almandine garnet. Its sharp, freshly fractured grains cut steel, titanium, stone, glass and composites, with less burr and taper than rounded river garnet. Four cutting grades run from fast-cutting 20/60 to fine 120#, with 80 mesh as the all-rounder.
Garnet is the waterjet standard. Abrasive is a third of the running cost.
An abrasive waterjet cuts cold, with no heat-affected edge. Ultra-high-pressure water draws the abrasive into the stream and accelerates it, and the abrasive does the cutting. Garnet is the industry standard,1 and because abrasive is about a third of a waterjet’s hourly running cost,1 the work each kilogram does goes straight to the bottom line.
- Ultra-high-pressure waterFrom the pump
- Jewel orificeForms a fine water jet
- Mixing chamberThe jet draws in GRM garnet
- Mixing tubeWater accelerates the grains
- Abrasive jetCuts steel, stone, glass and composites
Hard enough to cut fast without wearing out the mixing tube. Softer abrasives cut slowly; much harder ones erode the tube.1
The best grain is the heaviest one the stream can still accelerate to full speed, because it carries the most cutting energy.1
Grains break down at a measured rate into fresh, sharp edges, instead of shattering to dust in the tube or rounding off and dulling.1
Sharp, angular grains cut faster and leave better edges than rounded ones.2,3 GRM Garnet is crushed from hard rock.
Crushed hard-rock garnet cuts deeper and faster.
Most waterjet garnet is alluvial: river garnet whose grains were tumbled round on their way downstream. GRM Garnet is mined from hard rock and crushed, so every grain keeps sharp, freshly fractured edges. Hard-rock garnet cuts deeper and faster, with less burring, minimal taper and a better edge finish.2
| Crushed hard-rock garnet · GRM | River (alluvial) garnet | |
|---|---|---|
| Cutting speed | Cuts deeper and faster | Suited to standard, general-purpose cutting |
| Edge finish | Less burring, minimal taper, better edge | Acceptable where edge quality matters less |
| Breakdown | Fractures at a measured rate into new sharp edges | Starts rounded, so fewer sharp edges to cut with |
| Purity | 98% almandine | Varies with the deposit: ask for test data |
| Sizing | Crushed and screened to a published sieve analysis | Natural grading; consistency varies by source |
| Chlorides | 10–15 ppm | Ask for test data |
More parts per hour
Faster, deeper cutting gets more output from the same machine, pump and operator.
Less finishing
A cleaner edge with less burr and taper cuts the grinding and deburring after the cut.
Fewer stoppages
Oversize grains block the nozzle and excess fines cause sputtering.1 Tight sizing keeps the feed even.
A cleaner workshop
A dust plume when a bag is poured is a sign of excess fines, which hurt cutting.2
Choose the grade for the job.
Coarser garnet cuts faster and suits thick material. Finer garnet gives a narrower kerf and a more precise edge.2 80 mesh is the most widely used waterjet size.1
| Grade | Role | Use | Typical materials |
|---|---|---|---|
| 20/60 | Speed | Maximum cutting power for thick or hard material, including material over about 50 mm thick | Thick plate, titanium, nickel alloys, wear plate, stone, armoured glass |
| 50# | Speed | Fast cutting for thick or hard material | Thick steel, titanium, stone |
| 80# | All-rounder | The general-purpose grade and the most widely used waterjet size | Steel, stainless, aluminium, composites, ceramics, stone, tile |
| 120# | Precision | Narrower kerf and finer edge for detailed parts; reduces breakage and delamination | Glass, composites, laminates, ceramics, thin and brittle material |
Bars run from d10 to d90, the sizes 10% and 90% of the grade pass, on a log scale. Calculated from the GRM Garnet size chart.4
What to ask a waterjet abrasive supplier.
| Ask for | Why it matters | GRM Garnet |
|---|---|---|
| Garnet purity | Non-garnet minerals cut less well1,3 | 98% almandine |
| Origin and shape | Crushed, angular grains cut faster than rounded ones2 | Crushed hard rock |
| Hardness | Balances cutting speed against mixing-tube wear1 | 7.5–8.0 Mohs |
| Specific gravity | Heavier grains carry more cutting energy1 | 4.0 |
| Sieve analysis | Oversize blocks the nozzle; fines cause sputtering1 | Published for every grade |
| Moisture | Damp garnet clumps and can clog the feed2 | Non-hygroscopic |
| Chlorides | Salt ends up in the catch tank and on cut parts | 10–15 ppm |
Look after it on site. Store bags dry and indoors, away from cutting splash, fit a trash screen on the pressure pot, and never reuse garnet swept from the floor.2
Waterjet garnet: common questions.
Which mesh garnet is best for waterjet cutting, 80 or 120?
80 mesh is the most widely used waterjet size: a general-purpose balance of speed and edge quality. 120# gives a narrower kerf and a finer edge for detailed parts, glass and composites. For speed on thick or hard material, coarser 50# or 20/60 cuts faster; coarse grades suit material over about 50 mm thick.
What is the difference between hard-rock and alluvial garnet?
Alluvial (river) garnet was tumbled round on its way downstream. Hard-rock garnet, such as GRM Garnet, is mined and crushed, so its grains have sharp, freshly fractured edges. Hard-rock garnet cuts deeper and faster, with less burring, minimal taper and a better edge finish.
How much garnet does a waterjet use per hour?
Typically 0.34–1.1 kg per minute, depending on the pump, orifice and mixing tube. At a common 0.45 kg per minute, that is about 27 kg of garnet per cutting hour.
Can waterjet garnet be recycled?
Some high-volume shops run recycling systems that clean and re-screen spent garnet; results depend on the system. Never reuse garnet swept from the floor: it carries dirt and oversize that block the nozzle.
Why does garnet clog the mixing tube or nozzle?
Oversize grains block the nozzle, excess fines cause sputtering, and damp garnet clumps in the feed. Buy garnet with a published sieve analysis, store bags dry and indoors, and fit a trash screen on the pressure pot.
Can I use blasting garnet in my waterjet?
GRM’s cutting grades are the same 98% almandine as its blasting grades. What a waterjet needs is tight sizing, dry garnet and high purity, so choose a cutting grade (20/60, 50#, 80# or 120#) and check its sieve analysis.
Does garnet quality affect cutting speed and mixing-tube life?
Yes. Non-garnet minerals cut less well, rounded grains cut slower than angular ones, and inconsistent sizing causes blockages and sputtering. Garnet’s hardness of 7.5–8.0 Mohs cuts fast without the tube wear that much harder abrasives cause.
Specifications and further reading.
Other uses of GRM Garnet
Sources
- The Fabricator. Selecting the right waterjet abrasive.
- The Fabricator (2024). Best practices for managing waterjet abrasive.
- OMAX (2020). Not all abrasive is the same.
- GRM Garnet (2026). Product data sheet and size chart.
GRM Garnet values are typical and do not constitute a specification. Third-party figures describe garnet in general, not GRM Garnet, unless stated.