Tavannes / U.S. PAT 24 May 1904 -Broken Screw In Barrel Arbor

[Dave84]

Hi Everyone 

I hope you are all doing well. 

I am looking for some advice. During disassembly I had a screw head snap leaving nothing sticking out of the barrel arbor. I have raided a friends stash of arbors but we couldn't find the required size. (Overall height 4.80mm, lower pivot 0.79mm, upper pivot 2.06mm, lower barrel pivot 1.50mm) 

Alternatively, I have searched Ebay for a donor but the US PAT 24 MAY 1904 doesn't seem to come up with any results. I believe that it is a variant of the Tavannes Cyma Cal. 330/331/332/333 movements but there are no search results for these either. 

Can anyone recommend a solution for removing the screw or a source of parts for this particular movement as I seem to be coming up short.  

Many Thanks in advance 

Dave 

 

[Marc]

Ratchet wheel screws are usually of a length such that the underside of the head tightens against the ratchet wheel or the top of the arbor before the end of the threaded shank bottoms out in the hole in the arbor.

This should mean that if the screw head is sheared off through over-tightening, the threaded shank should still be free to turn within the arbor, and that means that you should be able to use the tip of a very sharp needle to back the remains of the screw out of the arbor.

Provided you had the correct ratchet wheel screw in there in the first place and not one that was too long you have a good chance of this technique working. The first thing to check on though is which way the screw turns as many ratchet wheel screws use a left handed thread and need to be turned clockwise to remove them (which is why they so often get sheared off when people try to undo them the wrong way).

Once you know which way to turn it you need a needle fine enough to get into the hole, and sharp enough for the tip to be able to engage in the rough broken surface of the remnants of the screw. Then good magnification and plenty of patience and some luck.

[Dave84]

15 minutes ago, Marc said:

Ratchet wheel screws are usually of a length such that the underside of the head tightens against the ratchet wheel or the top of the arbor before the end of the threaded shank bottoms out in the hole in the arbor.

This should mean that if the screw head is sheared off through over-tightening, the threaded shank should still be free to turn within the arbor, and that means that you should be able to use the tip of a very sharp needle to back the remains of the screw out of the arbor.

Provided you had the correct ratchet wheel screw in there in the first place and not one that was too long you have a good chance of this technique working. The first thing to check on though is which way the screw turns as many ratchet wheel screws use a left handed thread and need to be turned clockwise to remove them (which is why they so often get sheared off when people try to undo them the wrong way).

Once you know which way to turn it you need a needle fine enough to get into the hole, and sharp enough for the tip to be able to engage in the rough broken surface of the remnants of the screw. Then good magnification and plenty of patience and some luck.

Hi Marc and thank you

I have a decent stereo microscope I just need to find a good needle and the patience ..

I will have a go this morning and see what i can do.

 

[Dave84]

4 hours ago, Dave84 said:

Hi Marc and thank you

I have a decent stereo microscope I just need to find a good needle and the patience ..

I will have a go this morning and see what i can do.

 

 

4 hours ago, Dave84 said:

Hi Marc and thank you

I have a decent stereo microscope I just need to find a good needle and the patience ..

I will have a go this morning and see what i can do.

 

Gave it my best shot, it seems stuck stiff and wont budge. But thanks for the tip Marc, something i will definitely try first in the future. 

[rodabod]

If it is fairly well stuck then mount in the lathe and core out the screw. Then attach something into this new hole to provide a handle to turn  - you could use a taper pin for an interference fit, or epoxy a screw or rod in place.

[Nucejoe]

Alum will disolve the screw but would not affect barrel arbour.

 

[rodabod]

27 minutes ago, Nucejoe said:

Alum will disolve the screw but would not affect barrel arbour.

 

How is that physically possible?

[praezis]

25 minutes ago, Nucejoe said:

Alum will disolve the screw but would not affect barrel arbour.

 

Joe, both are steel. Should be a very smart sort of alum to distnguish one from the other

Frank

[Nucejoe]

I goofed up and will shut up.