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When you need supports (and how to avoid them)

The 45-degree rule, why supports cost money and spoil the surface, and design tricks to avoid needing them.

3 min read

Each layer rests on the one below. As long as an overhang stays within about 45 degrees from vertical, every layer has enough of the previous one beneath it. Past that, the plastic comes out into thin air and droops.

20°✓ no supports45°✓ no supports70°✕ needs supportsAngle measured from verticalRule of thumb: up to 45° prints in mid-air
Forty-five degrees is not an exact physical law, but it is a reliable design rule. Up to there, it prints unaided.

Why you want to avoid them

  • They cost material that goes in the bin and time you pay for.
  • They leave a mark. The surface they touched comes out rough and needs sanding.
  • Inside closed cavities they are hard or impossible to remove.

Tricks to avoid them

  1. 1Rotate the part. Often printing it upside down or on its side is enough.
  2. 2Turn round horizontal holes into a teardrop or diamond: they print unaided.
  3. 3Add a 45° chamfer where you would have had a flat overhang.
  4. 4Split the part into two halves that print flat and glue afterwards.

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