Venus 170 - Stripped Screw Hole

[sstakoff]

Hi there. I recently acquired a vintage Breitling chronograph - Venus 170 movement.

During reassembly, I noticed that 2 screw holes are stripped. One screw

is used to fasten the sliding gear spring and the other is for the hammer spring.

 

The screws look good - the holes seem to be the culprit. I can think of 3 options:

1. Fill the holes with silver solder or similar; drill and tap

2. Drill and tap a larger hole and find new screws

3. Attempt to close the hole a bit with a staking punch and retap

 

I would like to think that option #3 is viable as it seems most straightforward. I am interested

in your thoughts. Also - if that is a viable option, I believe the correct method is to use a round

faced solid punch to close the hole. Not sure what kind of stump to use?? Or do I sandwich

the plate between 2 round faced punches????

 

The 2 screws are highlighted with red arrows in the attached pic....

 

As an aside, once I fix the screws, the sliding gear spring itself (also in the pic) seems rather worn and

a bit rusted. It's not exerting quite enough force to move the sliding gear bridge which is causing the

watch to bind when it attempts to advance the minute register. I hope to make a replacement spring

to solve that problem.

 

Always an adventure :)

 

Stu...

 

[926wolf]

Hi Stu

well deforming the screw hole will work but i believe you would only be belling the ends its not a uniform deformation so when you rethread only a small portion of the re- cut thread will be there. Its a bit like leaving a burr and using the burr edge as the thread.

Maybe drill the hole out slightly larger and bush it. If you press in the bush with a very small interferance it should stay in place for drilling and tapping.You can always glue the bush in if needed. This way the hole centre stays true and would look a bit neater.

Silver soldering can be fraught with issues. As when you fill the hole you loose the centre so you would need to have a good guide or centering jig.

Dave (926wolf)

[clockboy]

Deforming the hole is a common trick with some repairers of clocks. However this can if not carful can deform the plate which causes other issues.

I would first try a new screw if this does not work then I would then try loctite 243 for medium strength or 603 for a stronger fix.

If the about does not work it will need re-tapping either with the same size or reaming out re-tapping & new screws fitted.

[Geo]

I would be inclined to tap it one size bigger and change the screws. The down side is you may have to enlarge the holes in the springs to accommodate. This would possibly involve drilling the springs with carbide drills.

[clockboy]

As you can see by myself & Geo's posts it is not a straight forward fix. If my memory serves me well I think Geo did a post on how to determine the thread size with pegwood. 

[Geo]

As you can see by myself & Geo's posts it is not a straight forward fix. If my memory serves me well I think Geo did a post on how to determine the thread size with pegwood.

In this case where the ordinal screws are present, I would measure them and go one size up providing there is enough metal in the spring to open up the hole.

[sstakoff]

As far as the loctite is concerned - are you recommending using the loctite to essentially fill [part] of the hole??

Or would I apply to the screw threads like normal? I don't want to do something that would make it too difficult to disassemble

the watch in the future...

 

Sounds like the "correct" fix is probably to drill/tap a larger screw....

[clockboy]

Just a touch of loctite on the thread of the screw.  When it dries it like a plastic & it might just give enough bite to hold. If you use loctite 243 it will still undo with a little force. However a bit of a bodge really but it might be worth a try because if it does not work no damage has been done.

 

However as they say the quickest way is normally the correct way i.e. re-tap the thread & if it does not work go up one size and fit new screws.

Have you tried new screws with the existing thread because that normally works.