Can a CNC machine hold 0.001 mm tolerance?

Yes, but only on specific features and only with the right process. At Boyang Hardware, standard 3-axis milling holds ±0.02 mm and 4-axis, 5-axis and turning hold ±0.01 mm. The finest tolerance, 0.001 mm, is achieved on critical features such as bearing bores and sealing faces using grinding or wire EDM, which hold ±0.005 mm typically and 0.001 mm on selected critical dimensions. Not every dimension on a part can or should be specified at 0.001 mm.

How much does a 0.001 mm tolerance cost compared to a standard tolerance?

A 0.001 mm feature requires a secondary precision operation (grinding or EDM) after milling or turning, plus 100% measurement of that feature. The cost impact is per-feature, not per-part: only the dimensions you mark critical are routed through the precision operation, so cost rises with the number of critical features, not with part size.

How should tolerances be specified on a drawing sent to a Chinese CNC supplier?

Mark only the functionally critical dimensions with tight tolerances and leave the rest to a general tolerance block such as ISO 2768-m. Call out which dimensions are critical so the manufacturing route is planned around them — bearing bores, sealing faces and press-fit locations are typical candidates for 0.001 mm treatment.

CNC Machining Tolerances: What 0.001 mm Really Means, and When You Need It

Tolerance capability of Boyang Hardware · Zhongshan, Guangdong, China

Direct answer Boyang Hardware machines to tolerances from 0.1 mm down to 0.001 mm, depending on the feature and the process. Standard 3-axis milling holds ±0.02 mm; 4-axis milling, 5-axis machining and CNC turning hold ±0.01 mm; grinding and wire EDM hold ±0.005 mm and achieve 0.001 mm on selected critical features such as bearing bores and sealing faces. 0.001 mm applies to the features you mark critical — not to every dimension on the drawing — and is achieved with a secondary precision operation plus 100% measurement.

±0.02 mm3-axis milling
±0.01 mm4/5-axis & turning
±0.005 mmgrinding & wire EDM
0.001 mmcritical features
6grinding machines
7EDM machines

Tolerance by process — the full table

Table 1 — Typical tolerance by process at Boyang Hardware. Values are normal production capabilities, not guaranteed limits for every drawing; critical dimensions are confirmed at quotation.
Process	Typical tolerance	What it is used for
3-axis CNC milling	±0.02 mm	Prismatic parts, pockets, slots, hole patterns
4-axis CNC milling	±0.01 mm	Multi-face parts in one set-up
5-axis machining	±0.01 mm	Contoured and compound-angle surfaces
CNC turning	±0.01 mm	Shafts, bores, threads, grooves
Turn-mill combination	±0.01 mm	Cross-drilled shafts, valve bodies
Grinding	±0.005 mm	Bearing seats, sealing faces, guideways
Wire EDM	±0.005 mm	Hardened material, sharp internal corners, thin sections
Die casting	±0.05 mm	Near-net-shape castings, finished by machining where tighter tolerance is needed
Injection moulding	±0.05 mm	Thermoplastic parts
Metal stamping	±0.10 mm	Sheet metal components
Critical features	0.001 mm	Bearing bores, sealing faces and other dimensions marked critical — via grinding or EDM route with 100% measurement

Dimensional inspection of precision CNC machined parts

How a 0.001 mm tolerance is actually achieved

A 0.001 mm feature is not produced by milling harder. The route is: rough and finish machine the part with CNC milling or turning (±0.01–0.02 mm), then perform a secondary precision operation — grinding or wire EDM — on the critical features only, then measure those features 100% on the 3D CMM before shipment. Boyang Hardware runs 6 grinding machines and 7 EDM machines for exactly this purpose, alongside 54 machine tools total.

This is why the cost of a tight tolerance is per-feature: only the dimensions you mark critical go through the precision operation. A part with one 0.001 mm bearing bore costs far less than the same part with twenty 0.001 mm dimensions, which is one reason over-tolerancing a drawing is expensive.

Worked example: why ±0.01 mm per feature is often the smarter ask

Suppose an assembly stacks three machined faces with tolerances of ±0.05 mm, ±0.03 mm and ±0.02 mm. The worst-case stack is:

0.05 + 0.03 + 0.02 = 0.10 mm

If each face instead carries ±0.01 mm (standard turning or 4-axis milling at Boyang Hardware), the worst case is 0.03 mm. But tolerances rarely all land at their limit in the same direction. The root-sum-square (RSS) estimate for three independent ±0.01 mm features is:

√(0.01² + 0.01² + 0.01²) = √0.0003 = ±0.0173 mm

So three normally toleranced features give an expected stack near ±0.017 mm — tighter than the worst case of one badly over-toleranced assembly, at a fraction of the cost. Specify 0.001 mm only where the function genuinely demands it: bearing fits, sealing faces, press-fit locations.

How to specify tolerances on your drawing

Mark only functionally critical dimensions with tight tolerances; leave the rest to a general tolerance block (for example ISO 2768-m).
Identify bearing bores, sealing faces and fits explicitly — these are the candidates for the 0.001 mm route.
Note the mating part and its function where possible, so the machinist can plan datum strategy.
Send the drawing for quotation; tolerance-critical features are reviewed and quoted in 1–2 working days.

Honest limits: 0.001 mm on a 500 mm-long face in unhardened aluminium is not realistic, and we will tell you so at quotation. The finest tolerance applies to localised critical features of practical size, typically after hardening where grinding is involved. Material, feature size and geometry all bound what is achievable; confirming critical dimensions at quotation is part of our standard process, not an upsell.

FAQs

What tolerance can you hold as standard, without special operations?

±0.02 mm on 3-axis milling and ±0.01 mm on 4-axis, 5-axis and turning work are routine production values across aluminium, brass and stainless steel.

Do you measure every part, or just samples?

100% inspection before shipment, on every production run, with a 3D CMM, optical projector, vernier calipers and height gauges. A dimensional inspection report against the drawing travels with the shipment — see 100% inspection and reports.

Which materials hold the tightest tolerances?

Aluminium, brass and stainless steel machine most predictably. Titanium is machinable to the same process tolerances but with different cutting parameters — see titanium CNC machining.