Reference
CNC Machining Tolerance Chart
Standard achievable machining tolerances by feature, and the full ISO 2768 general-tolerance table for dimensions you do not explicitly tolerance.
Tolerance is the single biggest cost driver on a machined part. This chart shows what shops typically hold without special effort, what is achievable with inspection, and the ISO 2768 general tolerances that apply to any dimension you leave uncalled-out. Rule of thumb: toleranced only the features that actually function, and let ISO 2768 cover the rest.
Typical achievable tolerances by feature
Standard is what most shops hold from a clean drawing. Precision assumes tighter process control and CMM or gauge inspection, which adds cost.
| Feature | Standard | Precision (inspected) |
|---|---|---|
| Linear dimension | +/- 0.005 in (0.13 mm) | +/- 0.001 in (0.025 mm) |
| Drilled hole diameter | +/- 0.005 in | +/- 0.001 in (reamed) |
| Turned / shaft diameter | +/- 0.002 in | +/- 0.0005 in (ground) |
| Flatness | 0.005 in | 0.001 in |
| Surface finish | 125 Ra as-machined | 32 Ra or better |
Typical values, not guaranteed until a shop quotes your specific part and material.
ISO 2768-1 general tolerances (linear dimensions)
Permissible deviations in mm for dimensions without an individual tolerance, by tolerance class (fine, medium, coarse, very coarse).
| Nominal range (mm) | Fine (f) | Medium (m) | Coarse (c) | Very coarse (v) |
|---|---|---|---|---|
| 0.5 to 3 | +/- 0.05 | +/- 0.1 | +/- 0.2 | - |
| over 3 to 6 | +/- 0.05 | +/- 0.1 | +/- 0.3 | +/- 0.5 |
| over 6 to 30 | +/- 0.1 | +/- 0.2 | +/- 0.5 | +/- 1.0 |
| over 30 to 120 | +/- 0.15 | +/- 0.3 | +/- 0.8 | +/- 1.5 |
| over 120 to 400 | +/- 0.2 | +/- 0.5 | +/- 1.2 | +/- 2.5 |
| over 400 to 1000 | +/- 0.3 | +/- 0.8 | +/- 2.0 | +/- 4.0 |
| over 1000 to 2000 | +/- 0.5 | +/- 1.2 | +/- 3.0 | +/- 6.0 |
Medium (m) is the most common default. State the class on your drawing (e.g. ISO 2768-mK).
ISO 2768-1 general tolerances (angular dimensions)
Permissible angular deviations by the length of the shorter side of the angle.
| Shorter side (mm) | Fine / Medium | Coarse | Very coarse |
|---|---|---|---|
| up to 10 | +/- 1 deg | +/- 1 deg 30' | +/- 3 deg |
| over 10 to 50 | +/- 0 deg 30' | +/- 1 deg | +/- 2 deg |
| over 50 to 120 | +/- 0 deg 20' | +/- 0 deg 30' | +/- 1 deg |
| over 120 to 400 | +/- 0 deg 10' | +/- 0 deg 15' | +/- 0 deg 30' |
| over 400 | +/- 0 deg 5' | +/- 0 deg 10' | +/- 0 deg 20' |
Values reflect ISO 2768-1 and common shop practice. Confirm the exact tolerance a shop can hold on your material and geometry before release.