Balance spring stud screw thread repair?

[BillM]

Hi All,

I'm working on a cheap movement and found that the threads for the balance spring stud screw are partially stripped.

What would be the proper way to fix this?

I have a small home machine shop and have been machining for years, so I believe I have the skill set to fix this, but I'd like to know how a professional watchmaker would repair this.

There's not enough material to move up a thread size, so would you drill it, plug it and then re-drill and re-thread it?

Thanks for any help with this.

-Bill

[nickelsilver]

What's the diameter of the stud screw you have? In the little sizes they tend to go in 0.05mm increments, like 0.30, 0.35, 0.40, 0.45, etc. I can see that the thread on your screw is not terribly well formed; if it measures for example 0.40, it may be that a screw from an assortment that measures 0.45 fits nicely in the remaining thread in the hole without having to resort to tapping. Taps in those odd increments are hard to come by, the normal supplier, Asco-Schurch, has 0.35 but otherwise jumps in even 0.10mm steps. In a pinch, you can file a tapered flat on a screw and use it as a tap in brass- especially in an already tapped but damaged hole, and it works quite well.

 

Cousins has good screw assortments like these.

[BillM]

The screw measures 0.41mm 

Good idea using a screw as a tap, I'll check out what size screws I have and see if I can make that work.

Thank you!

[BillM]

I found a slightly larger screw with a coarser thread in my stash of screws and filed a slight taper on the end.

I then put a drop of oil on it and used it like a tap, it took quite a few careful in and out turns to get it to go, but in the end it worked great!

Thanks for the great idea nicklesliver, much appreciated.  

Bill