Understanding dimensional tolerances for laser-cut parts. Learn about standard tolerances, factors affecting accuracy, and how to specify realistic requirements for your projects.
Introduction
Dimensional tolerances define acceptable variation in part dimensions and directly affect cost, quality, and functionality. Over-specifying tolerances increases cost unnecessarily. At Fulei Metal, we help clients understand and specify appropriate tolerances.
What Affects Laser Cutting Tolerances?
Material Factors
Thickness affects tolerances because thicker materials have wider kerfs and more edge taper. Material type affects cutting behavior. Material flatness causes inconsistent focal distance. Material stress can be released during cutting.
Machine Factors
Machine positioning accuracy sets the baseline, typically plus or minus 0.03 mm for modern machines. Beam quality affects spot size. TRUMPF lasers are known for exceptional beam quality. Thermal stability and calibration state also matter.
Process Factors
Kerf compensation must match actual kerf width. Cutting speed affects accuracy. Thermal effects cause expansion. Cut sequence influences thermal distribution.
Design Factors
Part size affects accumulated error. Feature complexity may reduce accuracy. Internal and external features have different characteristics.
Standard Tolerance Guidelines
General Tolerances
External dimensions: plus or minus 0.1 mm up to 100 mm, plus or minus 0.15 mm for 100-300 mm, plus or minus 0.2 mm for 300-600 mm, plus or minus 0.5 mm above 1000 mm. Internal: plus or minus 0.1 mm for holes up to 10 mm. Hole-to-hole: plus or minus 0.1 mm up to 100 mm.
Thickness-Dependent Tolerances
Up to 3 mm: plus or minus 0.08 mm. 3-6 mm: plus or minus 0.1 mm. 6-12 mm: plus or minus 0.15 mm. Above 12 mm: plus or minus 0.2-0.3 mm.
ISO 2768 Reference
Four classes: Fine, Medium, Coarse, Very Coarse. Most laser-cut parts fall within Medium.
Geometric Tolerances
Flatness
For thin sheet at or below 3 mm: 0.5-1.0 mm per 100 mm. For medium 3-6 mm: 0.3-0.5 mm per 100 mm.
Perpendicularity
Less than 0.05 mm for materials up to 3 mm. Less than 0.1 mm for 3-6 mm. Less than 0.2 mm above 12 mm.
Specifying Tolerances
Use the title block for general tolerances. Apply specific tolerances only where needed. Avoid over-tolerancing which increases cost. Perform tolerance stack-up analysis for assemblies.
Achieving Tighter Tolerances
Process optimization through parameter tuning. Material selection using stress-relieved material. Post-cutting operations like precision machining. Controlled environments with stable temperature.
Inspection and Verification
Calipers at plus or minus 0.02 mm. Micrometers at plus or minus 0.001 mm. Pin gauges for holes. CMM at plus or minus 0.005 mm. First article requires 100 percent inspection of critical dimensions. In-process checks every 10-20 parts.
Conclusion
Specifying appropriate tolerances is essential for successful projects. By specifying realistic tolerances, you ensure quality while controlling cost. At Fulei Metal, our quality system and advanced equipment enable us to consistently meet specified tolerances.
Tolerance Bands Worth Writing on the Drawing
Tolerance discussions go better when both sides work from bands rather than single numbers. These are achievable in routine production and are the values we quote against.
| Feature | Typical achievable | Note |
|---|---|---|
| Hole diameters up to about 20 mm | about ±0.05 to 0.1 mm | state it as a tolerance class rather than a list of individual values |
| Feature position | about ±0.1 mm | requires a clear datum scheme |
| General linear dimensions | ISO 2768 class m | name the class on the drawing |
| Edge squareness | ISO 9013 tolerance class | taper rises with thickness |
| Repeatability part to part | within the bands above | confirmed through first-article plus an agreed sampling plan |
| Press-fit intentions | state them in advance | the kerf is not zero and it is tapered |
Where drawings cause trouble it is rarely because a tolerance was too loose. It is because the same tight value was applied to every dimension, which makes it impossible to tell which features actually carry function. A drawing that names three critical dimensions and puts everything else under general tolerance will get a faster, cheaper and more reliable quotation than one that tries to control everything.
Frequently Asked Questions
What happens if we specify tighter than these bands?
It is possible on specific features, but it becomes a process rather than a setting — slower cutting, more checking, more frequent verification. Worth doing where it earns its cost and nowhere else.
Which dimensions are usually worth specifying tightly?
Those that mate, seal or carry load. Everything else runs happily on general tolerance, and keeping it there is the cheapest quality decision available.
Do you verify tolerances on every order?
Yes, first-article measurement as standard, and then either sampling or full inspection depending on what the purchase order asks for.
Questions about a specific part are usually faster to answer against the drawing — send it through the route below.
About these figures. The reference values above come from our own production range; inspection and reporting lists the machines and materials behind them, and DFM review explains the adjacent steps that change the result. For your own part, cutting capability is the fastest route to a quote — the earlier we see the drawing, the more of it can still be adjusted without cost. The tolerance context is set out in how these tolerances carry into forming.