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Expanding the inner hole of main spring.

Kevin W.

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Apr 11, 2002
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Hello all. I am working on a Seth Thomas recorder movement. I removed the thick springs from it and want to use thinner less stronger main springs. Problem is the winding arbour is quite large for a regular spring to install on it. I have a tapered punch and i have expanded the hole a fair bit ut not enough to get it on.I habe propane torch and was thinking of heating it and expanding more with my tapered punch. Any thoughts on this ?
 

Uhralt

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Sep 4, 2008
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I would try to avoid heating the inner coils because it is hard to control the heating and the cooling down in that area so that it is even on both sides of the spring and throughout the width of the coils. Usually the innermost coils are annealed anyway so I would just try to expand more, working from both sides of he spring.

If you can find or make a taper that is rather small and close to the desired diameter, that would help.

Uhralt
 
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bruce linde

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Nov 13, 2011
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I just had to make a hole in the end of a mainspring and I remembered a tip from brian fisher … to use a Dremel tool. It was so unbelievably easy I couldn’t believe it. Just a suggestion…
 

Kevin W.

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Apr 11, 2002
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Bruce its about getting the inner hole circle bigger to fit onto arbour. The hole that the spring catches onto the hook is fine.
 

Willie X

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Feb 9, 2008
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Do you have a steel worker's 'line up' punch. They have the correct taper to do this job. I wouldn't heat it either. Willie C
 

Kevin W.

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Apr 11, 2002
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I have this big alignment punch. I got it stretched a fair bit was having trouble to get it more expanded, which is why i thought about heat. I drilled a hole in a piece of wood and put punch through hole of spring with wood underneath.
 

Willie X

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Feb 9, 2008
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It takes a lot of force. You might have to use 'unnessary' force. Grease the drift and flip the spring over often. If you see that the hole is just expanding and contracting, you can try rewinding the spring from outside in. That's a better solution than trying to cut and rehole the inner coil. It does result in kind of a odd looking spring though. If you can cut off the outer end (which was the inner end) 5 or 6 inches before reholeng it, that helps some.

I have a photo here somewhere of a 'switched end spring'. I might have to post it later though. Willie X

20181127_163310.jpg
 

Kevin W.

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Apr 11, 2002
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Yes Willie, its very springy material so a a fair bit of force would be needed. Its a first for me, having to do this.
 

Kevin W.

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Apr 11, 2002
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Yes Willie, thats important , just try a bit at a time. Thanks for the help.
 

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