Laser cutting tolerances: what ISO 2768-m means
Every page on this site says we cut to ISO 2768-m. This guide explains what that means in practice: how far a dimension may vary, what that accuracy means for bolts, pins and tab-and-slot joints, and when a part needs work after the laser.
The short version
- ISO 2768-m sets how far a dimension without its own tolerance may vary. On a part from us it applies to every dimension.
- On a 100 mm part that is ±0.3 mm, on a hole up to 6 mm ±0.1 mm.
- That is enough, without rework, for clearance holes, tap drill holes, slots and cut-outs with some play.
- It is not enough for fits: press fits, bearing seats or pins that must sit without play. For those, have the hole cut slightly smaller and ream it.
What ISO 2768-m is
Not every dimension on a drawing carries its own tolerance. All dimensions without one then fall under the general tolerances of ISO 2768. The standard has four classes: f (fine), m (medium), c (coarse) and v (very coarse). We work to class m, and that is also what our terms promise.
The permitted deviation depends on the size of the dimension: the longer it is, the more room it gets. It applies to lengths, widths, hole diameters and hole spacing alike.
The limits in class m
Our parts are at most 1150 mm long, so the table stops at 2000 mm.
| Nominal size | Permitted deviation |
|---|---|
| 0.5 to 3 mm | ±0.1 mm |
| over 3 to 6 mm | ±0.1 mm |
| over 6 to 30 mm | ±0.2 mm |
| over 30 to 120 mm | ±0.3 mm |
| over 120 to 400 mm | ±0.5 mm |
| over 400 to 1000 mm | ±0.8 mm |
| over 1000 to 2000 mm | ±1.2 mm |
Three examples
- A 10 mm hole may measure between 9.8 and 10.2 mm.
- Two holes 100 mm apart, centre to centre, are between 99.7 and 100.3 mm apart.
- A 200 mm wide front panel is between 199.5 and 200.5 mm wide.
In practice most dimensions land well inside these limits. What we can promise, though, is the standard, and that is what you should plan with.
What fits without rework, and what does not
Clearance holes for bolts: fits
Draw the clearance hole, not the bolt size: 5.5 mm for M5, 6.6 mm for M6, 9 mm for M8. Even at the lower limit there is enough play. A hole of exactly 5 mm, on the other hand, will not reliably take an M5 bolt.
Tap drill holes for threads: fits
Have the tap drill hole cut with the part, for example 5.0 mm for M6, and just run the tap through afterwards. ±0.1 mm makes no difference to the thread. How thick the sheet has to be for it is on each material page.
Hole patterns that must meet a mating part: with clearance
Both parts have their own deviation, and in the worst case they add up. Add as much clearance to the hole diameter as the two tolerances together: a little over 0.5 mm for hole spacing up to 120 mm, about 1 mm up to 400 mm.
Tab-and-slot joints: with clearance
Draw the slot 0.2 mm wider than the sheet is thick. The sheet thickness has its own tolerance from the material standard, so a slot at nominal size often binds.
Cut-outs for displays, sockets and switches: with clearance
For a component that sits in the cut-out without a bezel, allow 0.5 to 1 mm of play. With a bezel or trim the gap disappears anyway.
Press-fit pins and shafts: rework
A fit such as H7 allows only a few hundredths of a millimetre at 6 mm. No laser can do that. Have the hole cut 0.2 to 0.3 mm smaller and ream it to final size.
Bearing seats: rework
Same as a press fit. A ball bearing needs a bore accurate to hundredths. Laser the hole smaller and ream or turn it.
What the standard does not cover
- Sheet thickness: it comes from the rolling mill and follows the material standard, not ISO 2768. A 2 mm sheet is not exactly 2.00 mm thick.
- Cut edge: the laser leaves fine striations and, depending on the material, a slight heat tint. With the “Raw” finish there can be a small burr on the underside; with either deburred finish we remove it.
- Flatness: large, thin parts can bow slightly from stresses in the sheet. ISO 2768-m says nothing about this. If a part has to lie flat, go one thickness up.
If you need it tighter
If your drawing has a dimension with a tighter tolerance, ask through the quote form before you order. Include the dimension and the tolerance. We will tell you whether we can hold it or what rework it needs.
You see the price before you order.