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Mounting Bridge on Cement Chuck And Achieving Center

SparkyLB

By SparkyLB
in Watch Repairs Help & Advice

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SparkyLB WRT Addict

SparkyLB

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I have an older scrap movement with a train bridge of the long slender variety.  It has two screws, one on each end, and contains only the jewels for the center wheel and the 3rd wheel.  Both jewels are rubbed in.  This is one of the first movements I bought, and did not have the ability to successfully free the jewel by the correct method.  Instead, I reamed out the hole using a .229mm reamer from my Seitz jeweling tool, and confirmed the remaining hole is parallel, sharp, and very clean.   

I purchased from Otto Frei a 2.30 mm OD jewel with the proper size jewel hole.  (The third wheel pivot measures .16mm, and the jewel I ordered has a hole of .17mm.)  I have recorded the depth of the original, badly cracked jewel before removing it.  Installing a new friction-fit jewel at the right depth should not be an issue.  

In retrospect, I would think I should have mounted the bridge on a cement chuck and using a lathe, and an appropriate tool; coax the rubbed-in metal open, allowing the rubbed in jewel to fall free.  My question stems from my inability to accomplish this. 

How does one mount an irregularly-shaped item (like this long curved bridge) on a cement chuck in order that the jewel hole is perfectly centered, and there is no wobble when the lathe spins?  I would be using shellac as an adhesive.    

I've searched about a bit, but as a novice, I probably don't yet know the correct questions to ask to get help from sources like google or youtube. 

My only option was to provide a long-winded explanation of my issue.  Any replies would help me greatly moving forward. 

 

 

 

nickelsilver Distinguished Member

nickelsilver

Posted
Posted

The easiest thing to do with plates and bridges is to cement them to another larger brass plate, then center this in the faceplate. The centering can be checked with a wobble stick or optically with a scope.

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SparkyLB WRT Addict

SparkyLB

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Thank you, nickelsilver.  You're always very helpful.  I'm guessing by faceplate you mean one of these?

faceplate.png.d4323bf0cf6aadb9240047b12271dcbb.png

If I only have a cement chuck, such as this:

1558227257_cementchuck.png.a66c8a26b52e614e5c9c1d1629f4fd55.png

can I still accomplish what you speak of?

I understand one can tap work into place on a faceplate.  A cement chuck would have to have the work affixed and in place in a very short window of time, i.e. before the shellac hardens.  Is this possible? 

Could one maybe mount a centering stake to the tailstock and while the shellac is hot, position the work onto the cement chuck mounted in the headstock with the jewel hole centered?  I appreciate everyone's patience.  I've taken Mark's 3 courses, and have probably spent days on YouTube, but I've never seen this scenario addressed. 

 

watchweasol Distinguished Member

watchweasol

Posted
Posted

Hi  The method mentioned by Nicklesilver is the preferred method but lacking the face plate the method you propose using the lathe and centering whilst the shellac is still soft is also possible. Both methods are explained in De Carles book "practical watch repairing" 

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