Screwing directly into 3D printed plastic
A screw can engage directly in a 3D printed plastic part when the joint is assembled only occasionally and enough material surrounds the hole. For repeated assembly, heat-set inserts or captive nuts are usually more repeatable. The required pilot hole depends on the screw, polymer and desired thread engagement.
Self-tapping vs machine screws
Plastic / self-tapping screws are designed to form threads in plastic.
Metric machine screws are primarily designed to work with a matching thread or nut. They may work directly in plastic in some cases, but they are not automatically the ideal direct-fastening choice.
Do not simply use nominal diameter
- Too small: excessive insertion torque
- Too small: cracking
- Too small: displaced material
- Too large: poor thread engagement
- Too large: stripped connection
Repeated assembly
For parts that are opened regularly, consider:
- heat-set insert
- captive nut
Reinforce screw bosses
Useful features can include:
- sufficient wall thickness
- ribs
- fillets at the boss root