Design
Layer orientation and part strength, with a worked example
A printed part is weakest across its layers. Orient the main tensile load along the layers.
HenleyPrint3D engineering2 min readUpdated Published
Key takeaways
- FDM shows the biggest difference between along-layer and across-layer strength.
- SLS differs little; orientation matters more for accuracy and surface.
- Add fillets or split the part when the load path runs across the layers.
- Verify with coupons in the orientations you will use.
Suits
Designers of brackets, clips and housings that carry load.
Worth knowing
FDM is weakest across its layers, so orient the main tensile load along them.
By process
| Process | Along vs across layers | What to do |
|---|---|---|
| FDM | Significant. Across-layer is the weak direction. | Orient the load path along the layers. |
| SLA | Moderate; changes with post-cure. | Post-cure fully; avoid thin features loaded across layers. |
| SLS | Small. Z can be a little lower than XY. | Orient for accuracy and surface. |
| PolyJet | Thin sections are weak in any orientation. | Orient for support and gloss. |
How to find the tensile face
- Mark where the part is loaded and which way it bends or pulls.
- Find the face that goes into tension.
- Orient the part so layers run parallel to that face, not stacked across it.
More design rules: design for 3D printing. Test coupons in your material give figures you can design with.
Order FDM parts through our FDM 3D printing service, or read about large-format printing up to 1000 mm.
Frequently asked questions
Which direction is a 3D printed part weakest?
In FDM, it is across the layers, along the build (Z) axis, where strength depends on the bond between layers. SLS and SLA are closer to isotropic.
How much weaker is a part across the layers?
Often 20 to 50 percent lower than along the layers in common FDM plastics, but it depends on material, temperature and layer height. Measure on your own process.
Should I always print flat?
Often. Flat printing aligns many load paths with the layers, but features such as pins or clips may be stronger or more accurate in other orientations. Check where tension acts.
Does layer height affect strength?
Yes. Thinner layers generally improve bonding and surface finish, but increase print time. The effect on strength varies by material and printer.
Is SLS isotropic?
Close to it. Z strength can be slightly lower than XY, and elongation can differ, but the gap is much smaller than in FDM.
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