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. |
Clearance for connecting & moving parts
When two parts are printed as an assembly — a hinge knuckle and pin, a lid in its housing, gears on a shaft — the gap between them controls whether they fuse into a single lump or move freely. The values below assume both faces are printed at the same orientation.
| Connection type | Gap per face | Typical use |
|---|---|---|
| Rigid connection (press / glue) | 0.2 mm | Two parts that should never move once assembled. |
| Loose connection (fastener pass-through) | 0.3 mm | Bolt or pin slides through, held by a separate clamp. |
| Sliding / moving fit | 0.5 mm | Hinges, lids, drawers, snap covers. Lower if your printer is well-tuned. |
Halve the gap if you're printing both parts separately and assembling afterwards.
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.
Got a part to print?
Upload your file and we'll quote it in seconds, engineer-reviewed before any charge.
Last reviewed May 2026 · Rigid Prints engineering team