Pre-tension a fusee

HughEvelyn

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Please would someone explain in simple words exactly how to pre-tension the lines on a fusee (the business of winding 3/4 to 1 1/2 turns of line on the drum)? It cannot be when fully wound (no give from the fusee) nor when unwound (too much give).
 

Christopher Lloyd Owen

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Aug 27, 2020
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I'm not quite sure I understand your question! I always have all the line on the spring barrel more or less as I know it should be, take up the slack, set up the spring on the click and wind the line onto the fusee. (If it's chain it's more tricky because pushing the chain around can scratch the barrel, so I'll set it on the drum much more carefully). I rarely have to push the line about too much, but that's practice.

But we may be talking at cross purposes.
 

Ralph

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I would think the 3/4 to 1 1/2 turns recommendation is to cause a capstan effect on the barrel, and also prevent a strain on the knot. When the fusee is fully loaded, with line or chain, without the spring wound, you can then give the fusee spring 3/4 to 1 1/2 turns on the spring to tension it. It’s a nominal setting that might need tweaking. You want to make sure the fusee stop, stops the winding, before the spring becomes full tight. You’ll strain the chain or cord if that happens.

Ralph
 

Jmeechie

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The easiest explanation is, you’re setting the spring in the middle of its strength or between fully wound and completely unwound. I usually pre tension the mainspring 1/2 to 3/4 turn. The technical is it was to balance the strength of the springs weaker unwound and stronger wound. Yes, the fusee accounts for the mainspring strength lessening as the clock runs down as it unwinds but the spring needs set in the centre of its strength curve.
It‘s also like the old Geneva stops where the spring is only working in the middle, not unwound nor wound tight.
This is really unnecessary to set anymore hence just adding a light tension at fully unwound.
Cheers,
James
 

bruce linde

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(just ran this by LaBounty to make sure i wasn't going to embarrass myself again! :rolleyes::))

after cleaning and servicing the movement:

1. with clock unassembled... attach cord/cable/chain to both barrel and fusee gear
2. reasemble but leave off the verge... apply oil where appropriate
3. wind all of the cord/cable/chain onto the barrel, spinning the barrel by hand, until the line between barrel and fusee gear is taut
4. at that point, add 3/4 to 1 1/2 turns to the barrel arbor using a key or letdown tool and secure the click so it can't move... this is the preload that adds a bit of tension to the mainspring
5. wind fully (fusee arbor), holding the escape wheel carefully so it won't spin
6. let the clock unwind, guiding the cord onto the barrel so it winds evenly and where you want it
7. install verge, wind, enjoy
 

Ralph

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I notice that I misspoke, the cord or chain should be on the barrel, not the fusee, when setting initial tension, the 3/4 to 1-1/2 turns.

As Bruce pointed out, you have to guide the chain/ line onto the fusee as you wind the lock the first time.

Ralph
 

Christopher Lloyd Owen

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Bruce has put it very neatly - except there is no need for number 6 in my view. Once it's on the fusee it will find its own way back onto the barrel as the clock goes, and it will always line in the same place - its place, not where you want it!
 

SuffolkM

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5. wind fully (fusee arbor), holding the escape wheel carefully so it won't spin
6. let the clock unwind, guiding the cord onto the barrel so it winds evenly and where you want it
On (6), just a caveat that running the clock at high speed here is not without risks. If you want to let the mechanism turn over to run the line/chain out onto the barrel and not wait 8 days, maybe press a finger lightly on the third wheel arbor (or basically any of the high speed arbors) as a brake. The power in a fusee movement is pretty significant, and the speeds otherwise are going to be excessive.

Michael
 

HughEvelyn

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You are all so kind. Thank you all very much indeed. Now I understand. But I have another question. If I have put it badly, I apologise: I've just brought 3000 mm (118") of bronze line which I have stupidly cut in half and am now worried neither piece is long enough!!! As with the Hubble Spacecraft, I got muddled between imperial and metric (so am in good company)! (The replaced pieces were 172 mm (67") - the striker - and 160 mm (63") - the train - respectively (total 3302 mm - 130"). If my loaded fusee takes 1390 mm (54 3/4") of 1.4mm (0.551") gut and the gap from the fusee line exit hole lying perpendicular to the drum tangent (i.e. the first touching point of the line on the drum from the fusee) is 27.5 mm (1 1/8") and the circumference of the drum is 185mm (7 1/4") what is the ideal length of the line from the line exit points on each drum and each fusee? (PS I am in UK trying to get my wife's 18th century fusee going again after yet ANOTHER gut snap. I used to live in Pa where this forum is based and regularly visited Lancaster County so I do appreciate answers from both sides of the pond (and elsewhere, if appropriate). Many thanks indeed.
 

Christopher Lloyd Owen

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I don't like wire line much, so now only use synthetic gut - unless the fusee is made for chain of course. (Worth checking - if the grooves in the fusee are curved, then they were made for line: if they have a squared base then they were made for chain.)

They are all pretty much standard size, and no need to cut because any excess can sit as an extra coil or so on the spring barrel at the front quite happily. I buy lines at the standard five foot (1.52m) from Wardles in the UK - less than £2 each + postage. Message me if you want their details.
 
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HughEvelyn

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I don't like wire line much, so now only use synthetic gut - unless the fusee is made for chain of course. (Worth checking - if the grooves in the fusee are curved, then they were made for line: if they have a squared base then they were made for chain.)

They are all pretty much standard size, and no need to cut because any excess can sit as an extra coil or so on the spring barrel at the front quite happily. I buy lines at the standard five foot (1.52m) from Wardles in the UK - less than £2 each + postage. Message me if you want their details.
Thank you Christopher. Yes, I have found Wardles. My lengths are still shorter than the standard lengths (1.52 or 5 foot) so I think I'll get anotherpair of lines! Thank you for both pieces of advice. Much appreciated.
 

bruce linde

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On (6), just a caveat that running the clock at high speed here is not without risks. If you want to let the mechanism turn over to run the line/chain out onto the barrel and not wait 8 days, maybe press a finger lightly on the third wheel arbor (or basically any of the high speed arbors) as a brake. The power in a fusee movement is pretty significant, and the speeds otherwise are going to be excessive.Michael
both my clock mentor and labounty said it’s ok if the movement has been cleaned and freshly oiled.... but labounty and i were talking and confessed that we always chickened out and used a finger to gently slow things down. :)
 
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HughEvelyn

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both my clock mentor and labounty said it’s ok if the movement has been cleaned and freshly oiled.... but labounty and i were talking and confessed that we always chickened out and used a finger to gently slow things down. :)
To Bruce and Suffolk - many thanks - note taken and will be very careful!! V good advice. Thanks!
 

Christopher Lloyd Owen

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I try never to let a train run at speed, Bruce, but it is quite fun! And it's a good way of spotting wheel wobble too.
 

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