It is frustrating and occasionally dangerous when cabinet door knobs pull off as you try to open the cabinet. Fortunately, repairing them is one of the easiest home-repair chores. If cupboard doors are opened and closed frequently, the wear they experience is to be expected. Before you replace the knobs, follow the steps below to make simple, and possibly permanent, repairs.
Diagnose your problem before buying supplies. Cabinet knobs come in two kinds. Type 1 is the simplest: the knob has a screw attached to it. The screw end goes into the cabinet wood. To make the knob work again, you need to use wooden matches and wood glue or plastic wood and a small putty knife to apply it. Type 2 knobs are just knobs with a hole in them. A hole goes through the cabinet door, a screw is fitted into that hole, and the knob is screwed onto the screw. For Type 2 knobs, you need the supplies for Type 1, but may also need new screws. If your Type 2 knobs are metal or ceramic, the threads holding the screws may have stripped, and you may need to start over with new knobs and screws.
Fix Type 1 knobs this way: The problem is that the hole in the cabinet has become too big for the screw. Break matchsticks into little pieces. Fill the hole in the door with wood glue and little pieces of matchstick--force them in hard. Alternatively, use wood filler compound and a putty knife to fill the hole. Wipe up excess glue or filler with a damp paper towel. Let it dry thoroughly. Now screw the Type 1 knob back into the hole. The tighter fit you have created should hold it fine, and you're done.
Fix Type 2 knobs this way: Apply your matchstick/glue strategy or the filler compound to the hole in the knob. Because you are putting the knob back on a blunt-end screw, hold the screw still with your screwdriver, put on a rubber glove to get a good grip on the knob, and screw it back on while your glue or filler is still damp. Wipe off any excess with damp paper towel.
Follow directions for Type 1 if your ceramic or metal knob has a screw attached to it. For Type 2 metal or ceramic knobs, you can force a little aluminium foil into the hole in the knob or wrap a small piece of foil around the screw to tighten the hold temporarily--this will keep you from losing the knob. Forcing a larger screw into a stripped socket (it's lost the threads to hold the screw) can jam halfway or even crack a ceramic knob. Use the time your emergency repair buys you to shop for new knobs and screws.