A fastener-free retention mechanism where a flexible cantilever deflects during insertion and snaps into a recess, locking two parts together.
Snap fits rely on controlled elastic deflection of a cantilever beam. Key parameters: deflection (y), permissible strain (ε ≤ 0.5× ε_yield), engagement depth (h), lead angle (α), return angle (β). Return angle determines retention force: β=90° = permanent lock; β<30° = releasable.
For FDM, print cantilever arm in XY plane (not Z) to maximize flexural strength. Minimum arm thickness ≥ 1.2 mm for PLA/ABS. Clearance on engagement face: 0.2–0.3 mm. Test 5–10 insertion cycles before production: FDM snap fits can stress-whiten or crack on first insert if strain exceeds material limit.
FDM layer lines are perpendicular to the bending stress in a horizontally-printed snap cantilever: inter-layer delamination is the primary failure mode. Reorient or reinforce if critical. PETG and TPU are more fatigue-resistant than PLA for snap fits.
Related terms: Living Hinge, Part Consolidation, Stress Concentration, DfAM (Design for Additive Manufacturing)
| Field | engineering |
|---|---|
| Also called | snap joint, cantilever snap, annular snap |
| Source | EDi Brain: rules-core |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert