Design guide
Tolerances & fits
FDM parts come off the printer slightly larger than CAD on outer features and slightly smaller on holes. Design with the actual numbers, not the wishful ones.
What to expect
Our typical tolerance on a Bambu A1 / P1S is ±0.2 mm on small features and ±0.3% of length on parts longer than 100 mm. That accounts for nozzle width, thermal shrinkage, and Z-step quantisation.
Outer features print oversized by roughly one nozzle width because the wall extrusion sits half on, half off the nominal edge. Holes print undersized for the same reason. Always design the assembly accordingly, don't expect a 10 mm shaft to fit a 10 mm hole.
Per-material tolerance
| Material | XY tolerance (±mm) | Length (over 100 mm) |
|---|---|---|
| PLA | 0.2 | ±0.3% |
| PETG | 0.3 | ±0.4% |
| ABS | 0.4 | ±0.6% |
| ASA | 0.4 | ±0.6% |
| PA-CF | 0.2 | ±0.3% |
| TPU | 0.4 | ±0.5% |
At 0.2 mm layer height with default print profiles. Tighter is possible, ask in checkout notes.
Designing clearances for fits
Pick a fit class first, then add the clearance per face. For a 10 mm hole running on a 10 mm shaft (a sliding fit), enlarge the hole by 0.15 mm per face, model it as 10.3 mm in CAD.
| Fit | Add per face | Typical use |
|---|---|---|
| Interference (press fit) | −0.05 mm | Heat-set inserts, pins you tap in. |
| Light press / location | +0.05 mm | Dowels, alignment features. |
| Running / sliding fit | +0.15 mm | Hinges, drawers, lids that close cleanly. |
| Loose / clearance fit | +0.3 mm | Captive nuts, bolts passing through, generous tolerance. |
| Generous (assembly) | +0.5 mm | Field assembly, gloved hands, snap-on covers. |
When tolerance really matters, prototype first
One test print of just the mating features costs almost nothing and saves you from re-cutting CAD on the whole assembly. We're happy to print a tolerance strip, drop us a note.
Why Z is different
Z-axis features are quantised to the layer height. A 5.1 mm step at 0.2 mm layers will print as either 5.0 or 5.2 mm, there's nothing in between. Either snap Z dimensions to a multiple of the layer height in CAD, or accept the ±half-layer uncertainty.
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Last reviewed May 2026 · Rigid Prints engineering team