Extracting a broken screw from a watch/bridge plate – Alum Powder

Ever since I was shown this method i have been waiting for a chance to document it and put it on the site, however its been a while since i have needed to extract a broken screw.

last week was given a movement in which the screw securing the crown wheel had been sheared off leaving the rest of the screw inside the bridge.

I have a learnt a few ways to handle this , one way is to (if possible) use a screw head file to try and make a ridge that you be then driven by a screwdriver to rotate the screw out. Another way is to drill out the screw.

If the above don’t take your fancy and your not in a rush i recommend Alum Powder.  Alum powder is by far the simplest method to solve this problem.


This stuff can be found in the spices section in most food shops and is very cheap. I managed to get a large bag for less than a few pounds and should last you forever!

What Alum powder does is dissolve steel. The process is slow, however can be sped up with heat.

All you need is to put the plate/bridge in a small bowl with some powder and some hot water and watch the process take place.  like i said you will need to wait a while (usually 1 – 2 days) however it is the safest way.  most of the plates are brass so they are fine in the solution but check that you don’t have other parts of steel in the plate as that will be gone when you come back.

Below are some snaps of the process and a video to show the powder in action.