Overhang angle and support in 3D printing
An overhang is a surface with nothing under it. Whether it needs support depends on the angle, the technology and the span. The angle is measured two different ways in practice, which is the most common source of confusion.
Two ways to measure the angle
From the vertical, 0° is a vertical wall and 90° is a flat ceiling. From the horizontal it is the other way round. A limit of 45° is the same surface either way, but 30° from the horizontal is 60° from the vertical. Dokimion states which one it uses next to every number.
| Technology | Needs support | Bridge without support | Note |
|---|---|---|---|
| FDM | steeper than 45° from vertical | up to 10 mm | support is removed afterwards and leaves marks |
| SLA | below 30° from horizontal | no separate limit | supports touch at points; put them on faces that can be sanded |
| SLS | none | not applicable | the powder around the part carries it; large flat faces warp instead |
| Metal LPBF | steeper than 45° from vertical, 50° for Ti6Al4V | up to 2 mm, 1.2 mm for Ti6Al4V | support is cut and ground off; horizontal holes over 8 mm (12 mm for Ti6Al4V) are overhangs too |
What support costs
Support is material, print time, removal work and a rougher surface wherever it touched the part. In metal it also has to be cut off and the surface ground. The report gives the support volume in cm³ and the area under support, so positions can be compared.
Islands and hanging points
A feature that starts in mid-air, a layer with no material under it at all, needs support whatever the angle. The check reports these separately from overhang surfaces.
How to need less support
- Rotate the part. Support often changes several times between positions, see part orientation and the gripper finger study.
- Use a chamfer instead of a ledge. A 45° chamfer prints without support where a flat shelf does not.
- Use a teardrop or diamond instead of a round horizontal hole that is too wide.
- Split the part where a large overhang can become two simple pieces.
- Keep support off the visible face. Choose the position so the support lands on hidden surfaces.
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