We had a plastic knob crack at the socket, which is frustrating, since the knob can no longer turn on and off. I tried my favorite quick adhesive, but the pressure of turning the plastic against a metal shaft was too much for it, so I brought out the big guns. I reinforced the shaft with a twist of wire (I used copper, which was at hand, but I think I would use stainless steel next time), then used a two-part epoxy around the wire, being careful to keep it outside the socket hole. I let it sit for a day before I tried the knob again. (When working with two-part epoxy, don’t throw away the mix cup until after it has hardened. This way you know when the epoxy on your piece has hardened as well.) Hurray! It worked, and the knob is still removable, just in case.