Guide · Replacement parts
How to design a replacement part for 3D printing
Recreating a broken part is less about copying its shape and more about understanding what it connects to. Engineers call these interfaces. Get the interfaces right and almost any shape in between will work.
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The method
- 01Identify the interfaces: every place the part touches something else (a shaft, a hole, a slot, a wall, a hand).
- 02Measure the mating parts with calipers, three times each.
- 03Decide the fit for each interface: press, snug, sliding or loose.
- 04Decide how it is used: how it goes in, what holds it, what force acts on it.
- 05Choose the print orientation so layer lines run along the main load and nothing needs supports.
- 06Choose the material: PLA for indoor/low heat, PETG for toughness and moderate heat, ASA outdoors.
- 07Print a quick test of just the interface (e.g. 3 mm tall slice of the shaft hole) before the full part.
- 08Adjust and print the final part.
Materials at a glance
| Material | Softens around | Good for |
|---|---|---|
| PLA | 55–60 °C | Indoor parts, prototypes, stiff clips |
| PETG | 75–80 °C | Snap fits, outdoor-ish, kitchen |
| ASA / ABS | 95–100 °C | Outdoor, car interior, near heat |
| TPU | — | Feet, bumpers, gaskets |
Frequently asked questions
Should I copy the original exactly?
No. The original was often injection moulded and failed for a reason. Keep the interfaces, then make the rest thicker or rounder where it broke.
Related
Updated · Generated parts are a starting point — always test-fit before relying on a part.