Functional Parts
Snap Fits, Clips, Living Hinges & Mounting Points
Design and print parts that actually work - clips that click, tabs that flex, and mounts that hold under vibration.
Functional Part Types
Snap Fits
Clips that flex and lock into place
Design: Add 0.3-0.5mm clearance, use gradual entry angles (30-45°), keep cantilever length 5x thicknessMaterial: PETG, Nylon, or PP for flexibilityLiving Hinges
Thin sections that flex repeatedly without breaking
Design: 0.3-0.5mm thick, print flat with layers parallel to hinge axis, round the transitionMaterial: PP or TPU only - others will crackSpring Tabs
Flexible fingers that apply pressure or grip
Design: Taper thickness toward tip, add relief cuts for more flex, test deflectionMaterial: PETG or Nylon for fatigue resistancePress-Fit Clips
Friction-based retention without snap action
Design: 0.1-0.2mm interference fit, add chamfers for insertion, consider taperMaterial: Any - depends on mating surfaceThreaded Inserts
Brass inserts heat-set into printed holes
Design: Hole diameter = insert OD - 0.2mm, 4+ walls around insert, vertical orientationMaterial: Any material works with proper techniqueMounting Bosses
Posts for screws or bolts
Design: Wall thickness 2x screw diameter, add gussets for strength, chamfer topMaterial: PETG, ABS, ASA for strengthTolerance & Clearance Guide
These values work for most FDM printers. Adjust based on your printer's accuracy.
| Fit Type | Clearance | Use Case |
|---|---|---|
| Press Fit (Tight) | -0.1 to -0.2mm | Permanent assembly, no fasteners |
| Friction Fit | 0.0 to 0.1mm | Removable but snug |
| Sliding Fit | 0.2 to 0.3mm | Parts that slide or rotate |
| Loose Fit | 0.4 to 0.5mm | Easy assembly, painted parts |
| Snap Fit Clearance | 0.3 to 0.5mm | Clips that need to deflect |
Snap Fit Design Parameters
Cantilever Length
5-10x material thickness
Longer = more flex, less forceDeflection
Max 2-5% of length
Stay within elastic limitEntry Angle
30-45°
Steeper = harder to insertReturn Angle
80-90°
Steeper = harder to removeWall Thickness
1.5-3mm
Thinner = more flexFillet Radius
0.5-1mm at base
Prevents stress concentrationMaterial Selection for Functional Parts
| Material | Snap Fits | Living Hinges | Threads | Fatigue | Notes |
|---|---|---|---|---|---|
| PETG | Good | Poor | Good | Good | Best all-rounder for functional parts |
| Nylon (PA) | Excellent | Fair | Excellent | Excellent | Best for high-stress clips, requires drying |
| ABS | Fair | Poor | Good | Fair | Brittle unless annealed, good with inserts |
| ASA | Fair | Poor | Good | Fair | Like ABS but UV stable |
| TPU | N/A | Excellent | Poor | Excellent | Flexible parts, gaskets, bumpers |
| PP | Good | Excellent | Poor | Excellent | True living hinges, hard to print |
Print Orientation for Function
Layer orientation is critical for functional parts. Flex across layers = delamination.
Snap-fit Clip
Orientation: Clip arm parallel to bed, deflection perpendicular to layers
Why: Layers resist bending forces, prevents delamination during flexLiving Hinge
Orientation: Hinge axis parallel to bed, flat print
Why: Layers run along hinge, flex between layers not across themMounting Boss
Orientation: Screw axis vertical (hole pointing up)
Why: Layers resist pull-out forces, stronger thread engagementBracket with Snap Fits
Orientation: May require splitting part or supports
Why: Optimize for the highest-stress featurePro Tips
Test snap fits at room temperature first - car interiors get hot and plastics soften
Add a small chamfer (0.5mm) to the leading edge of all clips for easier insertion
Design retention features with 10-20% extra strength for vibration resistance
Print test clips before committing to a full part - iteration is cheap
PETG is the best general-purpose material for functional clips in automotive
For under-hood or high-heat areas, use Nylon or glass-filled materials
Always add fillets at stress concentration points (corners, bases of tabs)
Frequently Asked Questions
Why do my snap fits break on first use?
Usually layer orientation - if the snap deflects across layer lines, it will delaminate. Print with layers parallel to the flex direction. Also check material choice - PLA is too brittle for functional snaps.
How do I design a clip that's easy to install but hard to remove?
Use different entry and return angles. A 30° entry angle lets it slide in easily, while an 80-90° return angle locks it in place. This is how OEM clips work.
What size hole for heat-set inserts?
Hole diameter = insert outer diameter minus 0.2mm. The insert melts into the plastic, so you want slight interference. Use manufacturer specs if available.
My threaded holes strip out - how do I fix this?
Use heat-set brass inserts instead of printed threads. If you must print threads, use 4+ walls, print with screw axis vertical, and use coarse thread pitch (M4 or larger).
Can I print working hinges?
True living hinges only work with PP or TPU. For other materials, print separate pieces and use a pin hinge, or design a snap-together hinge with clearance.
Troubleshooting
Snap fit too tight / won't insert
Increase clearance by 0.1-0.2mm. Reduce entry angle. Add chamfer to mating edge. Check for elephant's foot on first layer.
Snap fit too loose / falls out
Decrease clearance. Increase return angle to 90°. Check for shrinkage - some materials shrink 0.5-1%.
Clip breaks during flex
Wrong material (PLA breaks, use PETG/Nylon). Wrong orientation (layers should be parallel to flex). Add fillet at base to reduce stress concentration.
Heat-set insert pulls out
Not enough walls around insert (need 4+). Hole too large. Insert not fully seated. Add knurled or flanged inserts for more grip.
Press-fit falls apart
Interference too small - increase by 0.05mm. Material too slippery (PP, Nylon). Consider adding a retention feature or adhesive.
Ready to Print?
Browse the parts library for functional clips, brackets, and mounts with Verified Fit.