The Q1-Q5 Classification System
Waterjet cut quality is divided into 5 classes — Q1 the coarsest, Q5 a mirror finish. The classification is a global standard; CAM software (IGEMS and others) works on this scale when parameters are chosen.
| Class | Surface | Speed (relative) | Typical Application |
|---|---|---|---|
| Q1 | Very coarse — pronounced striation marks | 100% (the fastest) | Pre-cutting, hidden surfaces, prototypes |
| Q2 | Coarse — moderate striation | 75-80% | Internal parts, underside faces, work to be machined later |
| Q3 | Standard — acceptable | 60-65% | General industrial cutting, visible surfaces |
| Q4 | Smooth — good quality | 40-50% | Premium products, assembly-ready |
| Q5 | Mirror finish — no further work needed | 20-30% (the slowest) | Aesthetic decorative work, jewellery |
Speed vs Quality
The difference in speed between Q1 and Q5 is a factor of four to five. Cut the same material at Q1 and you will get four times as much work out as at Q5 — but the surface quality will be far lower.
Surface Quality in Detail
The factors that affect surface quality:
- JET ENERGY — pump pressure and nozzle setting
- CUTTING SPEED — faster cutting leaves a more striated surface
- GARNET QUANTITY — not enough garnet → quality drops
- NOZZLE CONDITION — a worn nozzle scatters the jet
- MATERIAL THICKNESS — thick material tends towards a wavy cut lower down
- STAND-OFF DISTANCE — the gap between the nozzle and the material
Thickness vs Quality — An Unavoidable Tendency
On one and the same part, cut at the same parameters and the same quality, the top surface and the bottom surface differ in quality:
- TOP SURFACE (jet entry) — always cleaner, close to Q5
- BOTTOM SURFACE (jet exit) — more striated in thick material, Q1-Q2
- TAPER — the bottom surface opens outwards from the top by 0.5-2° (depending on thickness)
- Compensation — a taper correction in the CAM according to material thickness
- In thin material (≤10 mm) this difference is minimal
- In thick material (>50 mm) it is pronounced — if you want Q5, very slow cutting is essential
Which Class for Which Job?
Q1 — The Fastest, The Coarsest
- Internal parts — not visible after assembly
- Rough shaping of a slab (to be machined afterwards)
- Prototypes — good enough as long as the dimensions hold
- High-volume series production — speed comes first
- Visual quality does not matter
Q2 — Coarse, Standard Industrial
- Mechanical parts (no visible surface required)
- Clamping faces (assembly points)
- Structural steel members
- Parts that will be welded afterwards
- Paint or coating to be applied — roughness is tolerated
Q3 — Standard Industrial (The Most Common)
- Most industrial applications — the default choice
- Marble slab cutting (to be polished afterwards)
- General sheet metal cutting
- A visible surface, but aesthetics are not the priority
- A balance of operating cost and speed
Q4 — Premium Visual
- Glass cutting (decorative)
- Kitchen countertop edges (before hand polishing)
- Architectural panels (visible)
- Logos and signage
- Products presented directly to the customer
Q5 — Mirror Quality, No Further Work Needed
- Jewellery (working gold and silver)
- Precision optical/electronic components
- Extra premium decorative work
- Works of art
- Very expensive material — waste kept to a minimum
The Operational Impact
| Factor | Q1 | Q3 | Q5 |
|---|---|---|---|
| Speed (relative) | 100% | 60% | 25% |
| Garnet consumption (relative) | 60% | 85% | 120% |
| Total cost (relative) | 70% | 100% | 180% |
| Acceptable error | High | Standard | Very low |
| Operator attention | Low | Standard | High |
The Optimum Strategy
For most jobs Q3 is the best balance — acceptable quality plus a reasonable speed. Q5 is only for work of high aesthetic value. Choosing "the lowest quality the job needs" for every job is the most economical approach.
Choosing the Quality in the CAM Software
In CAM software such as IGEMS and Contranest the quality is a single parameter — the software automatically sets the speed, the pressure and the garnet flow:
- The operator enters the material, the thickness and the quality
- The CAM generates the G-code automatically
- A different quality for a different contour on the same part (hybrid)
- For example: Q3 on the outer contour (not visible), Q4 on the edge profile (visible)
- This approach cuts the total time by 20-30%
Measuring Quality
- Visual comparison — against reference sample plates
- A profilometer (laboratory) — Ra/Rz measurement
- The customer standard — the acceptance criterion in the contract
- Q1: Ra >12 µm; Q3: Ra 3-6 µm; Q5: Ra <0.8 µm (approximate)
- Industrial customers generally stipulate "Q3 minimum"