Design decision framework for choosing between interference (force) fit, transition fit, or clearance fit based on required joint function.
ISO fit nomenclature (H7/p6, H7/f7, etc.) applies to AM only after calibration. Three zones cover most AM needs: clearance fit (gap ≥ tech minimum clearance) for moving parts; transition fit (±0 to ±0.1 mm) for locating features without play; interference fit (negative gap) for permanent retention.
Clearance fit: add tech minimum clearance (FDM 0.2 mm, SLA 0.1 mm, SLS 0.4 mm). Transition fit: set nominal equal and rely on AM tolerance scatter: always test-print. Interference fit: reduce hole diameter by 0.1–0.2 mm (FDM/SLA) or 0.05–0.1 mm (SLS/DMLS) from pin diameter.
AM tolerance scatter makes transition fits unreliable without test coupons. Never assume first-print success for tight fits. Asymmetric shrinkage (X vs Y vs Z in FDM) can turn intended clearance into interference. Always verify with a coupon at operating temperature for rotating fits.
Related terms: Clearance for moving / mating parts, Dimensional tolerance, Press-fit joint
| Theme | assembly |
|---|---|
| Also called | fit type selection, ISO fit class |
| Source | sources/2026-04/2026-04-24--3d-printing-best-practices-guide |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert