Design and tolerances
How do you design parts for 3D printing?
To design a part for 3D printing, keep walls above the process minimum (1.0 to 1.2 mm for FDM, 0.5 to 1.0 mm for SLA, 0.7 to 1.0 mm for SLS), keep FDM overhangs within about 45° of vertical, enlarge holes because they print undersize, avoid sealed cavities, and orient the part so the main load runs along the layers.
Reviewed by HenleyPrint3D engineers3 min readUpdated
Key takeaways
- Keep walls at or above the process minimum.
- Overhangs steeper than about 45° from vertical need supports (FDM).
- Holes print undersize. Add clearance.
- Orient the part so the main load runs along the layers.
Suits
Designers preparing a model for FDM, SLA or SLS.
Worth knowing
Walls must meet the process minimum, and FDM overhangs steeper than about 45° from vertical need supports.
Design limits by process: walls, supports and escape holes
| Feature | FDM | SLA | SLS |
|---|---|---|---|
| Minimum wall | 1.0 to 1.2 mm | 0.5 to 1.0 mm | 0.7 to 1.0 mm |
| Supports | Beyond about 45° from vertical | Required, light touch | None |
| Escape holes | Open build, no drain holes | Drain holes for hollows | 4 to 5 mm or more |
Design rules for 3D printed parts
Which process suits which feature?
| Feature | Most forgiving process |
|---|---|
| Thin walls and small details | SLA (0.5 to 1.0 mm wall) |
| Hollow or interlocking geometry | SLS, which needs no supports |
| Large parts | FDM, up to 1000 mm |
| Moving assemblies printed in place | SLS, with 0.3 to 0.5 mm clearance |
Design the part for the process you will use, then check the limits above before you export. Four checks catch most problems: wall thickness, overhang angle, hole size and orientation. If a feature fails a check, change the feature or the orientation before changing the process.
For why orientation affects strength, see layer orientation and part strength. For durable threads, see threaded inserts. If you want an engineer to adapt a model for printing, see our design and CAD services.
Frequently asked questions
What is the minimum wall thickness for 3D printing?
It depends on process. As a guide, about 1.2 mm for FDM, 0.5 to 1 mm for SLA, 0.7 to 1 mm for SLS and around 0.6 mm for PolyJet. Thicker walls survive handling and cleaning better.
How do I avoid supports in FDM?
Keep overhangs under about 45° from vertical, use chamfers instead of right-angle overhangs, split the part so each piece prints flat, and use teardrop-shaped horizontal holes.
How much clearance do 3D printed parts need?
Typically 0.3 to 0.5 mm for moving parts and 0.15 to 0.4 mm for close sliding fits, depending on process. Test a coupon in the real material for critical fits.
Can I 3D print threads?
Coarse threads can be printed for light duty, but they are weak and wear quickly. Heat-set inserts or tapped holes are the better choice for repeated assembly.
What file format should I send?
STEP is best because it preserves exact geometry. STL or 3MF meshes are acceptable if they are fine enough and watertight, in millimetres.
Get started
Talk to an engineer about your part.
Send us your CAD or describe the problem. We recommend the process, material and finish, and quote with the lead time up front.
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