Weak or brittle parts
Parts snap easily or break along the layers under a load they should handle.
Also described as brittle, weak, snaps easily, breaks easily, not strong, fragile
Try these in order
Most likely and quickest to check first. Change one thing at a time so you know what fixed it.
Load pulling layers apart
Prints are weakest between layers. A part loaded across its layers can be several times weaker.
- Rotate the part so the load runs along the layers, not across them.
Not enough walls
Walls add more strength than infill.
- Use 3 to 4 walls before raising infill.
- Use gyroid or cubic infill at 20 to 40% for functional parts.
Wrong material
PLA is stiff but brittle.
- Use PETG, ASA or nylon for parts that need to bend or take impacts.
Printed too cold or the filament is wet
- Raise the temperature a little and dry the filament.