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Position error

Smudgy

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May 20, 2003
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I'm working on a Benrus BM4 18/0s ladies watch. I've got a positional error of about 5 minutes stem down, all other positional errors are within 1 minute. The pivots are polished and have proper fit and shake, the balance is poised, the hairspring is concentric and flat, jewels are in good shape. I've even changed the balance, hairspring, and jewels in case there was something I couldn't see wrong. It's got me stumped and a bit frustrated :mad:. Does anyone have any ideas on what the problem might be? :confused:
 

Smudgy

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I'm working on a Benrus BM4 18/0s ladies watch. I've got a positional error of about 5 minutes stem down, all other positional errors are within 1 minute. The pivots are polished and have proper fit and shake, the balance is poised, the hairspring is concentric and flat, jewels are in good shape. I've even changed the balance, hairspring, and jewels in case there was something I couldn't see wrong. It's got me stumped and a bit frustrated :mad:. Does anyone have any ideas on what the problem might be? :confused:
 

Don Dahlberg

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Aug 31, 2000
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When the movement is stem down, what is the relative position of the balance staff to the pallet arbor? Is the balance above the pallet, below the pallet, or are they side by side?

I assume the watch is 5 minusts FASTER in the stemp down position?

Don
 

doug sinclair

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Aug 27, 2000
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Smudgy,

It sounds to me like an escapement problem! Does the pallet fork "skip" when manipulated by hand? If so, there might be a problem with the guard pin on the pallet fork dragging on the safety roller in the one position. Does the balance wheel motion look healthy in the one position? Do you have adequate corner freedom of the roller jewel in all positions? Have the banking pins been tampered with? They should be adjusted so that you have just enough corner freedom for the roller jewel, and a guard pin that is not dragging on the safety roller
 

Smudgy

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Don, The pallets are above the balance. Yes, the error was fast.

Doug, No skipping on any of the teeth. Guard pin doesn't drag anytime. The balance has just under 1 3/4 turns in horozontal positions, ~1 1/2 in vertical except stem down, and ~1 1/8 to 1 1/4 in sem down. The corner freedom is good and the banking pins as they were. I can't find a problem with the escapement.

I took it apart, recleaned it, rechecked everything, reoiled, and reassembled it about ten hours ago. It had a small glass chip on one of the escape wheel teeth. Can't figure where I picked that up, or why it would only effect it in one position. I checked it about an hour ago and it seems to be running OK now. I'll let you know how it's doing tomorrow, maybe that's where the problem came from and it will be running fine. I don't have a timing machine, so I'm on the slow adjustment schedule.

Thanks
 

LarFure

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Nov 30, 2003
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Smudgy,
For positional timing you could speed things up by using the 15 minute test. All you need is a stop watch. Time your watch with the stop watch for 15 minutes,take the differance fast or slow and multiply by 96 then divide by 60. That should get you in the ball park and help speed things up a bit.
 

Smudgy

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LarFure, I don't worry too much about the time aspect as long as I don't have to pay attention to it while I wait. I just set it down and work on something else, then come back and give it a look after a day has passed. I guess at some point I'll breakdown and get a timing machine, but for now the only time I get annoyed with the wait is when I'm vibrating a hairspring (usually takes most of a week to get to final adjustment).

It seems the chip of glass was the problem. The watch ran a little less than 1 min fast in 34 hours, which is close to what the other horozontal positions were. I'll run through the positions to make sure, but I think that was it. I still don't understand why it only effected the one position, though. I never would have found it without taking the watch to pieces, it was so small and clear. When i first saw it (under magnification) I thought it was a little spot of oil that had wandered out from where it should have been.
 

Don Dahlberg

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Aug 31, 2000
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A timining machine not only allows you to determine rates much fast, but the pattern of the trace would have pointed you to a bad escape wheel tooth, if that was really the problem.

The other day my carry watch started running fast. It turned out to be a cat hair riding the center wheel and playing with the escape wheel. The cats are not allowed in the watch room, but their fur does not follow the rules.

Don
 

Smudgy

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Diagnosis has been the reason that I've even considered a timing machine, but with this being a hobby with no income attached the cost of an expensive item with limited use has left it low on the list of things to get. I nearly bought one last year but ended up getting a stereoscopic microscope instead. Currently I'm working on getting a tool room sized engine lathe, well wanting to get one would be a better evaluation. The timing machine may come at some point in the next few years, but I'll just have to wait and see what happens with finances. Since I don't take in any work the time factor is negligable, and the trouble shooting takes a while but so far I've been able to track the problems down sooner or later. Life goes on... ;)
 

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