Tight tolerances on a laser-cut part are usually free in CAD and expensive on the shop floor. Here is where they actually matter, and where they quietly add cost.
A tolerance is a purchasing decision written in a drawing. Every time a designer types ±0.1 mm out of habit, somebody downstream decides whether to add an operation, slow a machine, or gauge a batch that would otherwise have shipped. On laser-cut sheet metal that decision gets made dozens of times per drawing.
What the process gives you for free
A well-maintained fibre laser holds roughly ±0.1 mm on profile within a single sheet, and that is genuinely free, it falls out of the process. What is not free is holding that same tolerance across a bend, across a weld, or across a batch cut from different coil.
- .01Cut profile within one sheet: ±0.1 mm, no cost
- .02Hole position within one sheet: ±0.1 mm, no cost
- .03Across a single bend: ±0.3 mm realistically, before springback correction
- .04Across two or more bends: stack the tolerances, do not repeat the tight one
- .05After welding: assume ±1 mm unless the part is fixtured and stress-relieved
Where the money leaks
The expensive pattern is a tight linear tolerance measured from a folded edge. The fold is the least repeatable feature on the part, so a ±0.1 mm callout from that datum forces either a secondary machining operation or a fixture that nobody quoted for. Reference the flat, not the fold, and the cost disappears without any loss of function.
The second leak is uniform tolerancing, the same block tolerance applied to all 40 dimensions on a sheet. Mating features usually account for four or five of those. The rest can sit on a general tolerance to ISO 2768-m and nobody will ever notice.
RULE OF THUMB · IF A DIMENSION DOES NOT TOUCH ANOTHER PART, IT DOES NOT NEED A SPECIFIC TOLERANCE.
K-factor is not a constant
Flat patterns generated with a default K-factor of 0.44 will be wrong on your press brake, because bend allowance depends on material, thickness, tool radius and the machine itself. The fix is a bend table built from your fabricator's test pieces, applied in CAD. Once it exists, first-off parts stop needing a trim.
What we do on issue
Every sheet metal pack we issue carries a general tolerance note, specific tolerances only on mating features, flat patterns generated against the fabricator's own bend table, and a DXF nested to the sheet size the shop actually buys. It is not more work, it is the same work, decided deliberately.