Another problem, seeking solutions..

Another problem, seeking solutions..

RonD.
RonD.

July 3rd, 2005, 3:32 am #1

I cleaned a pocket watch for a friend and ran it for a few weeks before returning it to make sure it was running good. I gave it to my friend only to have him tell me that it stopped a day or so later.

He dropped it off to me today to let me check it out and when I looked at it the balance wheel was all spastic! It was just shaking a little left and right real fast. Well I suspected it had somehow got magnetized, so I demagnetized it. Within seconds, it was back to running great.

It turns out that my friend had been traveling all last week and gone through a lot of airport metal detectors. I guess that was how the watch got magnetized. So maybe someone can explain how the metal detector would screw up a watch and how to get around it (without leaving the watch home).

Ron
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Joined: May 8th, 2005, 11:38 am

July 3rd, 2005, 9:31 am #2

It does sound like your friend's pocket watch's balance wheel got magnetized somehow. There are different ways to detect metal and most of them do not use strong magnetic fields. But, apparently the watch was exposed to a strong magnetic field that magnetized its balance wheel and the surrounding steel parts. Watches which have brass balance wheels are a lot less prone to this problem.

So, although you did not give the details of the movement, I would assume that the watch had a solid gold case and a steel movement with a steel balance wheel. Gold will not shield against magnetic fields.

The only way I can think of to prevent this problem in the future is for your friend to carry the watch in some sort of steel case when he is traveling. The outer steel case will act so as to prevent any magnetic fields from entering it and the watch it contains.

Another solution would be to replace the balance wheel with a brass one, but that can be a major watchmaking job.

technoguy
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Scott
Scott

July 3rd, 2005, 3:09 pm #3

I cleaned a pocket watch for a friend and ran it for a few weeks before returning it to make sure it was running good. I gave it to my friend only to have him tell me that it stopped a day or so later.

He dropped it off to me today to let me check it out and when I looked at it the balance wheel was all spastic! It was just shaking a little left and right real fast. Well I suspected it had somehow got magnetized, so I demagnetized it. Within seconds, it was back to running great.

It turns out that my friend had been traveling all last week and gone through a lot of airport metal detectors. I guess that was how the watch got magnetized. So maybe someone can explain how the metal detector would screw up a watch and how to get around it (without leaving the watch home).

Ron
One type of metal detector amounts to a loosely coupled radio transmitter and receiver tuned to the same frequency-a metal object will slightly detune it..but there shouldn't be any magnetic field anywhere near strong enough to magnetize a watch...maybe he left it near a power supply for the X-ray machine or something..Demagnetizing is easy enough-all you need is a coil big enough to put the watch(or whatever)into,and an AC power source(a low voltage transformer).Put the watch into the coil,turn on the power,and slowly pull the watch away from the coil..for the coil, I would use a 4 inch PVC pipe couple,wound with 1500 or so turns of,say,#28 guage wire,driven by a 12 to 24 volt transformer.(I used an old doorbell transformer). I had a homemade screwdriver magnetizer/demagetizer in my shop two jobs ago, built along those lines...
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Jack from Philadelphia
Jack from Philadelphia

July 3rd, 2005, 8:07 pm #4

It does sound like your friend's pocket watch's balance wheel got magnetized somehow. There are different ways to detect metal and most of them do not use strong magnetic fields. But, apparently the watch was exposed to a strong magnetic field that magnetized its balance wheel and the surrounding steel parts. Watches which have brass balance wheels are a lot less prone to this problem.

So, although you did not give the details of the movement, I would assume that the watch had a solid gold case and a steel movement with a steel balance wheel. Gold will not shield against magnetic fields.

The only way I can think of to prevent this problem in the future is for your friend to carry the watch in some sort of steel case when he is traveling. The outer steel case will act so as to prevent any magnetic fields from entering it and the watch it contains.

Another solution would be to replace the balance wheel with a brass one, but that can be a major watchmaking job.

technoguy
I would bet that your friend got the hand-wand treatment because he kept setting off the walk-through detector. I usually take off any watch I am wearing - metal or otherwise - and put it in the handy-dandy tray. Tray items are x-rayed, and this doesn't seem to bother wrist watches.
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RonD.
RonD.

July 3rd, 2005, 8:23 pm #5

You are probably right Jack. My friend travels light, usually with just what he can carry. The watch was a size 18 pocket watch, the kind with the balance wheel on the outside of the movement. It was in a silveroid display case, the type that has a crystal on both sides so you can marvel at the technology. He probably did get the hand wand treatment.. I'll have to ask him.

Ron
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