Stripped screw hole on barrel bridge

[ifibrin]

After repeatedly assembling and unassembling my ETA 7001 movement for practice, the screw hole for the click on the barrel bridge has finally stripped. Do I need to get a new barrel bridge, or is there something I can do?

The screw itself is fine, but the screw hole for the click on the barrel bridge is almost smooth, and I did see some small metal shaving on my bench. I was always extremely careful to put the screws in perpendicular to the hole, so I am not sure how this happened!

[ifibrin]

Here is a picture of the screw hole with the screw next to it.

[nickelsilver]

You could probably tap it the next size larger and fit a screw with the corresponding thread.

I like to keep things as original as possible, so I would bore out the old tube, making a small countersink on the underside, and make a new tube with shoulder that corresponds to the countersink, that presses in from the underside with enough friction that it will resist the torque of tightening the screw- which doesn't need much, and overtightening was probably why it stripped.

 

So no super easy fix unless you have taps and a good selection of screws, or the equipment to do the latter repair.

[ifibrin]

2 hours ago, nickelsilver said:

You could probably tap it the next size larger and fit a screw with the corresponding thread.

I like to keep things as original as possible, so I would bore out the old tube, making a small countersink on the underside, and make a new tube with shoulder that corresponds to the countersink, that presses in from the underside with enough friction that it will resist the torque of tightening the screw- which doesn't need much, and overtightening was probably why it stripped.

 

So no super easy fix unless you have taps and a good selection of screws, or the equipment to do the latter repair.

Is there anywhere I can get a selection of different sized screws? Prior to getting into this hobby I wasn’t even aware you could even make screws this small!

for the second method you suggested, I’m not sure if there’s a separate tube for the click screw to screw into. From what I could tell, it looks to be machined into the barrel bridge itself. Are you suggesting to drill out the entire raised “tube” with a bigger hole, then pressing in a new tube of the appropriate size, kind of like a brass bushing, then make the screw threads?

on another note, how many times do you think a movement can be taken apart and put back together for practice before the screw threads start becoming worn? The main plates are made of plated brass, so I imagine steel screws will eventually wear into the brass threads. I was also quite careful to not over tighten, but I suppose with small screws it can be difficult to tell.

[rodabod]

This may make some people cringe, but on cheaper watches, I wouldn’t be too upset if someone were to spread the hole to make it close with a round punch. It does not take much. Can re-tap the hole with a tap, but if you are careful then ca use the original screw. 

[Klassiker]

7 hours ago, ifibrin said:

how many times do you think a movement can be taken apart and put back together for practice before the screw threads start becoming worn

Hundreds If not thousands of times is my guess, as long as the threads are well formed on both parts, and the screw is not over-tightened. That is not to suggest that you did anything wrong, but you don't know the history of these parts.

Material houses sell screw assortments which are useful to hold in stock, sometimes sorted, sometimes mixed, and for different purposes e.g. balance, movement, case.

In your photo, what is the line running from the hole in the bridge out to the egde?

[ifibrin]

3 hours ago, Klassiker said:

Hundreds If not thousands of times is my guess, as long as the threads are well formed on both parts, and the screw is not over-tightened. That is not to suggest that you did anything wrong, but you don't know the history of these parts.

Material houses sell screw assortments which are useful to hold in stock, sometimes sorted, sometimes mixed, and for different purposes e.g. balance, movement, case.

In your photo, what is the line running from the hole in the bridge out to the egde?

I think that’s a stray hair.

From inspection of the click screw, there’s only two complete rounds of threads, so I suppose the click screw hole on the barrel bridge might have the weakest screw thread in the movement. It would only take one turn at an off angle of the screw to destroy the half of the threads.

Edited June 2, 2021 by ifibrin

[Nucejoe]

 Considering your watch repair tools don't yet include a lathe on one hand and eta 7001 is cheap, your cheapest and easiest option would be to glue the screw into the hole, using metal glue. make sure all parts are clean, put the click and spring back on, oil, next  apply glue inside the hole specially on threads, press the screw home. Needless to say if the hole has an opening on the other side you best add more glue there, if it doesn't you should apply most glue without any gushing out as you press the screw in place. Be prepaired to whip in case glue spreads to where its not suppose to.

Good luck pal.