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A question of torque....  Rate Topic 
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 Posted: Wed Jun 23rd, 2010 04:37 am
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Elicius
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I wasn't quite sure which area to put this in, but I figured it fitted here as well as anywhere [feel free to re-locate it though!].

I am presently a student fast-approaching my final-year of an HND in Horology. During this final year, we are required to 'build' a functional clock or watch.

[By build, I mean - on the most part - rehouseing movements, replanting trains and things like that; 'though one of the present years class built a regulator from scratch....which was nice, heh]

I hope you don't mind, but I'd like to ask a question;

For my project, I aim to re-case a movement, and improvise a simple case-winding mechanism for same. So my question is this:

Does anyone happen to have a rough estimate of the torque required to:

A) Simply wind the watch [lower/minimum torque],

and/or

B) Once a movement's
[any medium sized, hand-wind mechanical (sub seconds and calendar display preferably, but I imagine they're mostly similar) would do, but I'm hoping to use an old Peseux 336N, but may be forced to resort to the 7001] mainspring reaches full wind, to do damage to the movement [highest possible torque].

If I had a relevant tool, I'd simply borrow a 7001 and test it, but sadly I'm out of college now, and most, if not all, tools are out of my price-range until student loans come through, heh.

I shall let you guys know how it goes either way though.
Thanks in advance for any help/advice,
Eli.

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 Posted: Tue Jun 29th, 2010 12:21 pm
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deadlyapp
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The first question is easily answered, but without a very very fine force measuring device I can't tell you. It's on the scale of a hundredth of a Newton though I'm willing to bet.

You would know better than I, but with the very efficient gear trains in most modern watches, the force multiplier from the stem to the mainspring probably negates any change you might "feel" as feedback. Thats why most winding watches have some sort of clutch system - which may be as simple as a plate with a specific friction coefficient that will not grip the mainspring barrel once it reaches a certain preset.

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 Posted: Tue Jun 29th, 2010 12:34 pm
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bigrustypig
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deadlyapp wrote: The first question is easily answered, but without a very very fine force measuring device I can't tell you. It's on the scale of a hundredth of a Newton though I'm willing to bet.

You would know better than I, but with the very efficient gear trains in most modern watches, the force multiplier from the stem to the mainspring probably negates any change you might "feel" as feedback. Thats why most winding watches have some sort of clutch system - which may be as simple as a plate with a specific friction coefficient that will not grip the mainspring barrel once it reaches a certain preset.

Whew....I read this for 10 minutes and still couldn't get itsubtlelaugh.gif. Thanks for the technical tidbit. I learned a lot.ThumbsUp02.gif

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 Posted: Wed Jun 30th, 2010 05:38 am
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deadlyapp
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bigrustypig wrote: deadlyapp wrote: The first question is easily answered, but without a very very fine force measuring device I can't tell you. It's on the scale of a hundredth of a Newton though I'm willing to bet.

You would know better than I, but with the very efficient gear trains in most modern watches, the force multiplier from the stem to the mainspring probably negates any change you might "feel" as feedback. Thats why most winding watches have some sort of clutch system - which may be as simple as a plate with a specific friction coefficient that will not grip the mainspring barrel once it reaches a certain preset.

Whew....I read this for 10 minutes and still couldn't get itsubtlelaugh.gif. Thanks for the technical tidbit. I learned a lot.ThumbsUp02.gif

Honestly I don't know crap about watches, but as a mechanical engineer I can kinda visualize some of it.  Anything I know about watch movements I've read and the technical information in most articles is zilch.  I'm relatively sure though that turning the stem does not directly turn the mainspring, it goes through several gears in order to exert more force, and then that force is transmitted back into a seperate gear train that runs the hands and timekeeping portion.

The force the spring exerts is simply a function of how much it has "deflected" - or been wound.  As it becomes less wound the force it exerts is lower - which would affect the time keeping, hence why they use gears to manipulate it.
http://en.wikipedia.org/wiki/Mainspring

Edit: more about causing damage to the spring.  I read through that wiki article (which is extremely good by the way), and as I said above, most autos already have some sort of clutch system in place that will sufficiently keep the watch from "overwinding"

With an older watch without such a system, you could in fact exert too much force - enough to possibly snap the mainspring or at least stretch it inelastically.  You'd have to do a pretty detailed spring analysis though and know the metallurgy of the material in order to tell what that would be.  You could make some educated guesses that would probably work though if you set the slip point low enough.

Last edited on Wed Jun 30th, 2010 05:45 am by deadlyapp

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 Posted: Sat Jul 31st, 2010 10:55 pm
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Elicius
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Thanks for the in-depth replied deadlyapp, much appreciated.

I think I'll probably go with two plates ['though possibly a manual adjustment on the outer-most, just to be on the safe-side]. I was tempted to dig out my old Newton-Meter from Comprehensive School, but think trial and error would probably suit me as well if I'm going for an adjustable.

I will however keep this thread bookmarked for the Mk II, heh.

In case you're interested, here's a maquette I stuck together for a deadline at college: http://tinyurl.com/32o6p68

As the plan stands the winding mech will be embedded in the uppermost runner, and work on a recessed wheel in the winding button.

Thanks again for the help!


{EDIT:} Also, as you can maybe see in the photo, the movement I aim t'use for this is automatic, so it has the slip-clutch you mentioned. While this is only a budget movement, I hope the end-of-the-line movement will be a touch classier. {/EDIT}

Last edited on Sat Jul 31st, 2010 10:57 pm by Elicius

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 Posted: Sun Aug 1st, 2010 02:39 am
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KenC
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Excuse me, but I thought Newton's Law was ....."One fig per cookie!"  subtlelaugh.gif

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 Posted: Sun Aug 1st, 2010 05:24 pm
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Elicius
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Man, I so didn't get that. But google to the rescue! I've always just known those as "Fig rolls". Ahh you folk with your Name Brands ;)

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