Machining
General tolerances ISO 2768
In short
Classes f, m, c, v: untoleranced linear sizes, chamfers and angles.
Applies to drawing dimensions without a written tolerance. The title block gives the class: f fine, m medium, c coarse, v very coarse; “ISO 2768-m” = medium class. A second letter (H, K, L) refers to the geometrical tolerances of ISO 2768-2, not covered here.
Linear sizes: ± deviation (mm)
| Size (mm) | f | m | c | v |
|---|---|---|---|---|
| 0.5to 3 | 0.05 | 0.1 | 0.2 | — |
| > 3to 6 | 0.05 | 0.1 | 0.3 | 0.5 |
| > 6to 30 | 0.1 | 0.2 | 0.5 | 1 |
| > 30to 120 | 0.15 | 0.3 | 0.8 | 1.5 |
| > 120to 400 | 0.2 | 0.5 | 1.2 | 2.5 |
| > 400to 1000 | 0.3 | 0.8 | 2 | 4 |
| > 1000to 2000 | 0.5 | 1.2 | 3 | 6 |
| > 2000to 4000 | — | 2 | 4 | 8 |
Below 0.5 mm, the deviation is written next to the size. Broken edges: next table.
External radii and chamfers: ± deviation (mm)
| Size (mm) | f and m | c and v |
|---|---|---|
| 0.5to 3 | 0.2 | 0.4 |
| > 3to 6 | 0.5 | 1 |
| > 6 | 1 | 2 |
Angles: ± deviation by the shorter side
| Shorter side (mm) | f and m | c | v |
|---|---|---|---|
| ≤ 10 | 1° | 1° 30′ | 3° |
| > 10to 50 | 0° 30′ | 1° | 2° |
| > 50to 120 | 0° 20′ | 0° 30′ | 1° |
| > 120to 400 | 0° 10′ | 0° 15′ | 0° 30′ |
| > 400 | 0° 5′ | 0° 10′ | 0° 20′ |
Deviation in degrees (°) and minutes (′) of arc.
Sources
Tools · Machining
Cutting speed and feedN, Vf, power and removal rate for turning, milling and drilling, with catalogue starting values.ISO 286 fitsHole and shaft limits, clearance or interference, any class a to zc up to 500 mm.Threads and tap drillsTap drill for cutting or forming taps, pitch and minor Ø, depth: M, UNC/UNF, G, Rp, Rc, NPT.Tightening torquesTorque and preload of a metric bolt by class and friction (VDI 2230), minimum preload by method.Bolt circleX/Y coordinates of n holes on a circle or arc, hole spacing, full-size marking template and DXF.TapersTaper ratio, angle, compound setting and tailstock offset; Morse, metric and chuck tapers.Measuring over pinsThree-wire measurement and best wire; over-pin measurement of a male or female dovetail.Hardness conversionHRC, HB, HV, HRB and tensile strength of steels, from ISO 18265.Turning surface finishTheoretical Ra and Rz from feed and nose radius, max feed for a target Ra, N classes.Machining timeCutting time for turning, facing at constant Vc, drilling and milling, per part and per batch.