Reference
Tolerances by Process
What each process holds as standard, what it can hold when you ask, and why the tighter number costs more.
Direct answer: standard production tolerances are ±0.10 mm for laser cutting and sheet metal forming, ±0.05 mm for stamping, ±0.01 mm on turned features and ±0.02 mm on milled features for CNC parts, and DIN 1688 / GB-T 6414 grade for as-cast die castings. Tighter values are possible but must be marked on the drawing, because inspection time and reject risk rise with precision.
Standard and achievable tolerances
| Process / feature | Standard | Achievable with effort | What drives the cost |
|---|---|---|---|
| Laser cutting, profile | ±0.10 mm | ±0.05 mm on thin small contours | Nesting, thickness, edge quality, inspection |
| Sheet metal forming | ±0.10 mm, ±0.5° | ±0.05 mm on short flanges with fixtures | Tooling, springback control, fixture and gauging |
| Metal stamping | ±0.05 mm | ±0.02 mm with fine blanking | Die precision, die maintenance, material variation |
| CNC turning | ±0.01 mm | ±0.005 mm on selective diameters | Tool wear, thermal stability, gauging |
| CNC milling | ±0.02 mm | ±0.01 mm on selective features | Fixture rigidity, tool deflection, in-process measurement |
| Die casting, as cast | DIN 1688 / GB-T 6414 grade | One grade tighter on selected dimensions | Die design, thermal balance, alloy |
| Die casting, machined | ±0.02 mm | ±0.01 mm on bores with fine boring | Fixture, datum choice, machining allowance |
| Surface roughness | Ra 3.2 µm as cut or machined | Ra 0.8 µm; Ra 0.4 µm by grinding | Extra operations, polishing time |
- Inspection time – a ±0.01 mm feature on a CMM takes longer to measure than a ±0.1 mm feature
- Reject risk – the closer the tolerance band to the process capability, the higher the scrap rate
- Process choice – a tolerance may force machining where stamping would have been enough
- Fixtures and gauges – tighter tolerances usually need dedicated fixtures rather than a vice and a calliper
- Machine time – slower feeds, smaller cuts and temperature control
Practical rule: hold tight tolerances only on the features that mate, locate, seal or conduct. Every other dimension can stay at the general tolerance without affecting function.
GD&T, datums and the drawing
Form and position tolerances are read from the drawing, not assumed. Where a part has several mating features, define the datum scheme first – the same part can pass or fail depending on which face is used as the datum. We inspect against the datums you specify and report the measured values, so the result is comparable with your incoming inspection.
If a drawing carries no datum scheme and no GD&T, the part is manufactured and inspected to the general tolerance and the dimensions as drawn. That is workable for simple brackets and risky for assemblies, so it is worth spending ten minutes on the drawing before tooling starts.
| Finish | Thickness added per surface | Where it matters |
|---|---|---|
| Zinc plating | 5 – 15 µm | Threads, press-fit holes, mating faces |
| Nickel plating | 3 – 10 µm | Bores, shafts, contact faces |
| Silver plating | 1 – 5 µm | Contact faces, busbar joints |
| Tin plating | 1 – 10 µm | Terminals, press-fit zones |
| Anodising | 5 – 25 µm (Type II), 25 – 50 µm (Type III) | Threads, bores, sliding fits |
| Powder coating | 60 – 100 µm | Mating faces, threads, earth points |
1. Set the general tolerance
Put a general tolerance block on the drawing (for example ±0.10 mm for sheet metal) so every untoleranced dimension has a defined limit.
2. Mark the critical features
Tolerate only the features that mate, seal, locate or conduct. Mark special characteristics visibly so inspection focuses on them.
3. Define datums for position
Use GD&T with datums for hole patterns and mating faces rather than chain dimensions from an edge.
4. State finish and coating allowance
Give the coating system and thickness, and state whether threads and bores must be masked or allowed for.
5. Ask for the DFM note
Send the drawing before tooling. A tolerance that cannot be held reliably is cheaper to change on paper than after a rejected batch.
Frequently asked questions
What is your standard tolerance if the drawing has none?
If no tolerance is stated we apply a general tolerance of ±0.10 mm to cut and formed features and ±0.5° to bend angles for sheet metal parts, and ±0.02 mm to milled and ±0.01 mm to turned features for machined parts. Anything tighter must be on the drawing.
Can you hold ±0.01 mm on a stamped part?
Not reliably in serial production – stamping is held to ±0.05 mm, and ±0.02 mm is achievable with fine blanking on suitable geometry and material. If a feature needs ±0.01 mm, it is usually cheaper to machine that feature after stamping than to force the die.
Do you inspect to the drawing or to a sample?
Inspection is against the drawing, and the report states which dimensions were measured, with what equipment and at which stage. Sampling frequency is defined in the control plan for the part, and 100% inspection of critical features is quoted separately.
How does plating affect my tolerance?
Plating and coating add thickness on every coated surface – 5 to 15 µm for zinc, 60 to 100 µm for powder coating. Threads, press-fit holes and sliding fits need allowance or masking, and that is decided before production, not after.
Not sure whether your tolerance is realistic?
Send the drawing with the critical dimensions marked. The quotation comes back with a DFM note on any tolerance that cannot be held reliably.