Print orientation and strength

Layers are the weak direction

A printed part is strong along its layers and weak between them. Pull the layers apart and it breaks at a much lower force than when you pull along them. How much weaker depends on the material and the print temperature, but half the strength is a normal figure.

So the question for every part that carries a load is: which way does the force go, and can the layers run along it?

Examples

• A wall hook: print it lying on its side, so every layer has the full hook shape. Printed upright, the hook snaps off at a layer line.
• A clip that has to flex: the arm that bends should lie flat on the bed, so it bends along the layers.
• A screw thread or a thin pin: these are stronger printed lying down, but rounder printed upright. For a pin that carries load, lying down wins.
• A box or a bin: upright is fine. The walls carry very little load.

Walls matter more than infill

Most of a part's strength is in its outer shell. Going from 2 to 4 walls adds far more strength than going from 15% to 40% infill, and often uses less plastic.

• Decorative parts: 2 walls, 10–15% infill.
• Holders, brackets and clips: 3–4 walls, 20–30% infill.
• Parts under real load: 5 or more walls, 40% infill or more, and a tougher material such as PETG.

Other things that help

• Print a little hotter. Layers bond better at the top of the temperature range of your filament.
• Round the inside corners. A sharp inside corner is where cracks start. Many tools here have a corner radius or fillet setting.
• Around screw holes, the slicer adds walls automatically, which is why a hole in the model is stronger than one you drill afterwards.

The orientation the tools use

Models from this site arrive in the slicer in the orientation they were designed to print in. For load-carrying parts such as hooks and brackets that is already the strong one, so leave it as it is unless the print tips say otherwise.