Print orientation: avoid pulling layers apart
FDM parts are anisotropic: they do not have the same strength in every direction. A part can be strong within a printed layer and fail much earlier when a load pulls adjacent layers apart. For functional parts, print orientation can therefore matter more than simply increasing infill.
Why FDM is direction-dependent
Filament is deposited line by line and layer by layer. Within a layer, material forms continuous roads. Between layers, strength depends on how well the new material bonds to the previous layer.
Wall-hook example
Poor orientation: the main load pulls directly across layer interfaces. Better orientation: extrusion paths follow the loaded arm as effectively as possible.
Flat is not automatically best
Printing flat may reduce support, improve certain surfaces and improve layer direction — but not always. Angled printing can sometimes create a better mechanical compromise. CNC Kitchen's orientation tests show large differences in tensile strength between different print directions. The exact test numbers are not universal, but they clearly demonstrate anisotropy.
- reduce support
- improve certain surfaces
- improve layer direction
Four questions before slicing
- Where does the main load act?
- Where is the likely failure point?
- Do layer interfaces cross that load path?
- Can another orientation improve the load path?
Trade-offs
A mechanically stronger orientation may mean more of the following. Choose the best overall compromise.
- more support
- different surface quality
- longer print time
- harder bridging