For some reason the poising tool is one of those watchmaker tools that you can find anywhere. There always seems to be one at every flea market, in every used tool store, and of course in every watchmaker’s shop. In fact, there are two in my shop. One is my personal poising tool, the other belongs to the store. A quick search one eBay yields 8 poising tools in good condition with bids starting as low as $6.99. Why can’t I find an escapement meter or heater at that price?
A well poised balance wheel is an essential element for a watch to tell accurate time. A poised balance wheel is one whose center of gravity exists at the center of the balance staff. If the center of gravity is not in the center of the balance wheel, gravity will affect the balance wheel differently when the watch is in different positions resulting in a larger variance of rates between the different positions. (See timing variations.)
There are two ways to “poise” a balance wheel. One is to remove the hairspring and statically poise the balance wheel. The second is to dynamically poise the balance wheel while it is installed in the watch based on timing results. When dynamically poising it is important to be sure that there are no other problems with the watch or you may end up with a balance wheel like the one I wrote about on Friday. There is a good article about this in the latest issue of the Watch & Jewelry Review.
The poising tool is used for static poising. First the poising tool has to be perfectly level and the ruby jaws need to be clean and static free. The balance with hairspring removed is placed on the jaws (like in the picture). The wheel is lightly rotated. If it turns freely and comes to a rest it has a heavy spot. If it can be stopped at any position around it’s circumference then it is properly poised. If it has a heavy spot a small amount of metal is removed from the underside of the rim of the balance wheel (or from the shoulder of the screws if it is screwed). The process is repeated until the balance is poised. If you remove too much material than you end up making more holes in the balance wheel and eventually you end up with swiss cheese so it is best to go slow.
6 Comments
Hi,
great explanation just 3 questions
For balances with screws do you mean the side of the screw metal is removed from?
Is there a special tool for removing metal from the screw?
Can the weight be adjusted by moving the screws out?
Thanks
David Prendergast
For balances with screws the screw is removed from the balance. Metal is removed from the shoulder of the screw (on the threaded side so that it doesn’t change the appearance of the screw. There is a special tool for doing this and I’ll use it for my tool next Tuesday. Some screwed balances also have timing screws which can be adjusted for rate changes. These should not be used to poise the balance but rather opposite screws should be moved equally to maintain the poise of the balance.
thank you so much, i am a retired machinist, i have a passion for old elgin timepieces, recently purchased a ruby jawed poising tool,vintage w/ box. as a rookie wanna be watchmaker, icould only find info on this tool from you beautiful instrument i bought off of ebay for 16.00 thanks again eddie boykin
just read email sent about poor watchmaking and used parts, as a retired machinist and wanna be watchmaker, this article could save many from like errors, however this displyed an absence of pride in workmanship thanks for the info. eddie
Have you come across a rolex screwdriver sharpener or a rolex ultrasonic poising tool? Also, Why would you ever want to remove any metal from a balance wheel with screws? Why wouldn’t you just add a washer 180 degrees from the heavy spot/ the light spot?
Hi Ellen,
I have yet to see a screwdriver sharpener that is specific to Rolex. They do supply their watchmakers with the proper equipment to hollow-grind their screwdriver tips, though, which yields a more effective concave edge, as opposed to a flat edge.
Rolex’s poising tool isn’t ultrasonic, but it does vibrate in a way that you could say is similar to that of an ultrasonic machine. It’s fantastic!
With regards to timing washers and balance screws. Timing washers should always be added to a balance in opposing pairs and not singly. They are timing washers, not poising washers. Poising a balance and bringing a balance to time are two different operations. It would be a shear stroke of luck to achieve perfect poise by adding a washer. Removing a very small amount of material from the underside of a screw is far more precise.
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