I was cleaning some built up calcium deposits in my shower and I noticed that the backplate for my shower handle had only one screw, so went to put another and noticed the screw was broken off in the threaded hole. I'd like to be able to use the threaded hole with a new screw but can't get this one out. Unfortunately the front of the screw is basically flush with the metal so can't grab it from the front, and there's not a lot of room to get a wrench behind it to twist the screw. Open to any suggestions.
There are special "thread extractor" drill bits for such cases.
But if the screw still slightly sticks out of the metal, get a hacksaw and cut a horizontal line in the bit that sticks out, then use screwdriver to screw it out.
You can also try a regular steel drill that is smaller than threaded hole - use manual drill, lean your mass on it so it "bites" into the metal, then try twisting clockwise to push the screw out the hole.
Ranked from "professional" to DIY:
- Get a screw extractor tool or bit for your drill. The thread on this is reversed, so it screws in as the screw comes out.
- If you have a small rotary tool and metal cutting ring, use it to "notch" across the top of the screw. This will allow you to stick a flathead screwdriver in and unscrew it. It looks like the screw protrudes a bit from the housing, but you have to be careful to not cut the housing as well probably.
- If you have a good wrench you can try to squeeze hard on the tail of the screw and turn it. If you squeeze too hard it might flatten the threads and make it hard to fully remove the screw (although maybe you could go the other direction).
Also, for all of these, spray some WD-40 on the screw to loosen it a bit.
It appears the broken screw may be contacting something at its tip (or nearly so). Use a small rotary cutting tool ("Dremel" or similar) to cut off the tip so that there's room for the stud to be driven all the way through the flange of the valve.
Select a drill bit smaller than the screw itself. Drill into the center of the broken screw. If the surface of the broken screw is not flat then a center punch may help coax the drill bit into starting in the correct place. A bit of grinding with the rotary tool may also help dress the surface for better drilling.
If all goes well the cutting action of the drill bit will actually cause the broken screw to rotate. It'll wind itself through the flange of the valve and fall out the rear side.
If all doesn't go that well then removing the stud toward the front, ie opposite the direction it went in, with a screw extractor probably wasn't going to work either. In this case choose a new screw, get the matching tap and appropriate drill bit, and drill and tap the hole for the new screw.