Yet another mainspring question

mr_byte

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Nov 25, 2009
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Hi all, I have a wall-hanging porcelain time-only wall clock with a german movement of unknown, but probably less-than-40-years-old make. It needs a mainspring, it's a smaller 3/8' wide spring. I only have the last few turns that were left on the arbor, the rest is gone. It's an 8-day movement, and I'd like to get a spring for it. Looking at Timesaver's 8-day springs, they are all 96" long. That seems a bit large to me. Is there a way to calculate the length of spring I need? I can get pics etc if needed, I realize my description fits about a gazillion or more clocks.
 
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Willie X

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mr_

You have the most important thing, the thickness. Measure the thickness of the piece that is left with a GOOD micromete, or cut it into ten pieces, stack them one on top of the other and measure with any kind of micrometer and divide by ten. Ok now you have the strength, measure the width of the old spring and the inside diameter of the barrel. You can look at the charts in the mainspring list to get the spring that goes in the size barrel that you have.

From your description this might be a Jauch movement, most of these have a good replacement available.

Good luck, Willie X
 

mr_byte

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Willie X;538650 said:
mr_

You have the most important thing, the thickness. Measure the thickness of the piece that is left with a GOOD micromete, or cut it into ten pieces, stack them one on top of the other and measure with any kind of micrometer and divide by ten. Ok now you have the strength, measure the width of the old spring and the inside diameter of the barrel. You can look at the charts in the mainspring list to get the spring that goes in the size barrel that you have.

From your description this might be a Jauch movement, most of these have a good replacement available.

Good luck, Willie X
Well, I have a harbor freight special, mic, but it's digital at least... There's no barrel, it's an open loop-end spring. No pendulum, it has a balance wheel(?) The rest of the movement seems ok, if I put a load on the mainwheel the balance will keep moving once started.
 

shutterbug

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You could figure out the ratio between the driving wheel and the center wheel (and the large wheel if it's not the driver). Then compute how many turns the large wheel has to make in 8 days. After that, calculate how much spring will be taken up winding that many turns. That's your length.
 

RJSoftware

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Sometimes there is a small post to prevent the open coils from rubbing on other gears and pinions. You could make a decent estamate if your calculated a little smaller than that.

But, open springs generally are wrapped arround the nearest plate post/pillar. So basically you could cut the extra off as long as you had enough to go arround the post.

I use propane torch to heat the spring enough to make the loop. It's easy.

RJ
 

mr_byte

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RJSoftware;538750 said:
Sometimes there is a small post to prevent the open coils from rubbing on other gears and pinions. You could make a decent estamate if your calculated a little smaller than that.

But, open springs generally are wrapped arround the nearest plate post/pillar. So basically you could cut the extra off as long as you had enough to go arround the post.

I use propane torch to heat the spring enough to make the loop. It's easy.

RJ
Cool. Thank you very much!
 

Willie X

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Mr_

Yes, having the thickness and width, just order the longest loop end one you can fine. Hopefully it will be long enough to run a week. To long usually is not a problem.

Willie X
 

mr_byte

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Willie X;538788 said:
Mr_

Yes, having the thickness and width, just order the longest loop end one you can fine. Hopefully it will be long enough to run a week. To long usually is not a problem.

Willie X
Willie X,
 

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Rockford's early high grade movements by Greg Frauenhoff