Friction welding 3D prints
Turns out 3D printed stuff can be welded with a rotary tool. When a piece of filament is mounted in a rotary tool and spun against a 3D printed object, the friction causes enough heat to melt the plastic. This can be used for welding 3D prints together.
The joints created this way are surprisingly strong, and under stress it is more likely that the object breaks somewhere near the joint than the joint itself failing. Friction welding works with ABS as well as PLA.