Removing broken timing screws

[JohnC]

Hi all,

I need a bit of help here. In trying to turn a mean time screw I have sheared off the head on my 18s Waltham. Pics attached. Not worried about the ruined screw but I need to find a way to safely remove the remainder. It's not protruding at all on the outside so pin vise is not an option. Any help appreciated. Thanks.

[clockboy]

Possibly a very fine drill. It has to be removed and replaced for the balance to be balanced. 

[nickelsilver]

It will have to be drilled. As you probably don't have a jig boring machine, the safest bet would be to drill it out by hand, rotating the drill in a pinvice. Most important thing is to get it in the center of the broken screw, for this you can take a piece of carbide or hard steel and grind 3 flats at 120 degrees to each other, at about a 40 degree angle to the end. Use this to carefully make a start pip, then drill through. Move up in drill size until you are right at the threads, you can then pick out the remaining bit. If it goes as planned the threads in the balance will be OK and you can fit a new screw.

[JohnC]

@nickelsilver
thanks. Others have recommended drilling enough to insert a broach, and then attempting to screw it either out or through. Thoughts?

[nickelsilver]

6 minutes ago, JohnC said:

@nickelsilver
thanks. Others have recommended drilling enough to insert a broach, and then attempting to screw it either out or through. Thoughts?

Yes, that can work, but don't break the broach!

 

Sometimes if you're lucky the drilling will actually screw it on through.

Edited May 20, 2021 by nickelsilver

[JohnC]

1 hour ago, nickelsilver said:

Yes, that can work, but don't break the broach!

Oooh yes, good point. Okay, first some oil and then I will attempt that. If it seems like the broach will break I'll try to drill out to the inside diameter of the screw. Many thanks. Just swapped the staff so the last thing I want to do is source a balance. I want to get past the "balance complete" stage.

[Flagstaff]

I had a broken screw in a mainplate recently - there were some female threads visible so I screwed in a screw with the same thread (full length undamaged screw) which grabbed the end of the broken screw and it came out fairly easily. Perhaps I was lucky, and it does rely on the broken thread having little or no tension on it - if the threads are distorted and tight it will likely not work.  

It was a much better solution than trying to drill it out without damaging the threads. It does rely on having a few "empty" threads though. Not sure from your photo if you have any? 

[Nucejoe]

Hi John,  In case there is some empty thread, a quick but imperfect approach is to file down a new screw just short enough to fit what thread is left, try to shelac the screw thread to keep it from loosening.

 

 

[JohnC]

@Flagstaff thanks but it's very stuck and I don't see any empty threads. @Nucejoe yes hopefully won't come to that but we'll see what I can do with the drilling.