Printed parts rarely come out at the exact modelled size — materials shrink as they cool and nozzles over-extrude slightly. For parts that fit together, design in a clearance of roughly 0.2–0.4 mm, test with a small tolerance gauge, and adjust for the specific material and printer.
Why parts don't fit
Two things fight your dimensions: thermal shrinkage as the plastic cools (worse for ABS/ASA than PLA), and slight over-extrusion that makes holes smaller and pegs larger than modelled. A 10 mm hole often prints closer to 9.7 mm.
Designing clearances
- Loose/sliding fit — ~0.4 mm gap between mating surfaces.
- Snug/press fit — ~0.2 mm, and expect to persuade it together.
- Threads and pins — add clearance or model them slightly oversized/undersized.
- Always print a small test coupon before committing a big part.
How 3D3D handles it
For parametric and made-to-order parts, we tune clearances to the exact material and printer and, when it matters, print a test fit first. Send your measurements and where the part goes — dialling in tolerance is part of the job, not an afterthought.