I am working on learning more about escapements and timing. The current patient (loosing about 4 minutes per day) has a problem in that someone has put in a hairspring that is not matched well to the weight of the balance (my hypothesis). The hairsping and balance vibrate out at about 293 bpm using the balance cock as hairspring vibrator. Regulator is set to fastest seting and the meantime screws are already in as far as they will go.

I can either shop for a new hairspring or remove weight from the balance. Since it is an overcoil, and I haven't mastered that skill yet, I'm leaning towards reducing the weight of the balance. I am equiped to undercut the balance screws, but where does one begin? The wheel is already in poise. Is my best bet to reduce weight in the neutral zone of the balance wheel, then bring it back into poise? Can I hope to reduce the weight sufficiently to bring the beats per minute back up without substantial effect to the balance?

Thanks in advance for sharing the knowledge...

Mike Miller
NAWCC Member# 154831
NAWCC-IHC Charter Member# 27

Mike,

First off, thanks for the Waltham staff P/N. I posted a thank you but it disappeared!

Does the watch run about 4 minutes slow in dial up, dial down, pendant up and pendant down? Has it been recently serviced?

Four minutes a day is really nothing. From "S" to "F" on your regulator will only correct for about 1-2 minutes per day. If you had a hairspring that was too strong or too weak, it would be more like an error of 40 minutes or more per day. I put a strength #3 hairspring in a 16s size Elgin and it ran 15 minutes fast per hour! Before adjusting your balance, you may want to consider the following:

1. Does the overcoil fit correctly between the regulator curb pins? Too loose and the regulator has little effect.

2. Are both balance jewels in good shape and properly lubricated?

3. Is the beat set correctly?

4. Does the balance have a good swing?

5. Are all of the screws tight?

6. Is the balance clean? Cleaning the balance may remove enough tiny foreign objects to get you closer.


If you have screw undercutters, try the following:

1. Set the regulator back to the center position.

2. Undercut the mean timing screws and/or the next adjacent screws to the mean timing screws. CAUTION, repeated installation and removal of the mean timing screws may cause them to become too loose and back out during operation. DO NOT undercut any screws near the cut end of the wheel or it will affect heat and cold timing. Carefully watch how much material is cut from each screw and try to approximate the same amount of removal from the opposite screw on the balance (180 degrees). Since the watch is in poise, a balance scale should be used to check the weight of the pair after cutting.

3. Choose which screws you are going to undercut and reomove just a small curl from each opposing screw. That should be enough for four minutes. If too much was removed, you can back the mean timing screws out, in even turns.

4. Check your watch timing and repeat if necessary.

5. Plan to spend some time doing this and be patient!

John D. Duvall
Rosamond, CA.

Mike,
Have you checked to see if the watch has the correct mainspring and that it is not set?
Brian C.

Mike,

Brian makes a good point. Wind the watch fully and check the timing (with an accurate source) for one hour (I use a garden variety quartz chronograph that's accurate to within a second per week to check my watches). If it still loses approximately 10 seconds, then most likely it's not the mainspring.

A little more history on the watch would help.

John D. Duvall
Rosamond, CA.

Brian,

I thought about the mainspring also. I replaced it a while back, and have tried a couple of different strengths. Still it was slow.

John,

Thanks for the step by step and advice. I have checked the initial steps that you post. The timing is consistantly off in all positions. Which lead me to believe that it was a balance weight problem. Just for kicks, I removed the two balance screws that were closest to the meantime screws, and the watch gained several minutes per day, so I know that reducing weight will have an effect. Perhaps my understanding of Poising the balance needs clarification. When a wheel is in poise, does that mean that the weight is perfectly distributed? By reducing the weight of two screws, doesn't that cause reduced weight in that particular part of the balance even though, the oposite side has been reduced equally?

I knew I should have never picked up that book by Purdom on Scientific Timing

Mike Miller
NAWCC Member# 154831
NAWCC-IHC Charter Member# 27

Mike,

A balance in poise means that it is just perfectly balanced, not a perfect distribution of weight. If the weight were perfectly distributed, your balance would have to have at least 360 identical timing screws or be solid and uncut.

It's really no different than balancing a tire on your car. When the mechanic adds a correct amount of weight 180 degrees opposite to the heavy side of the wheel, the wheel becomes poised or balanced. The weight was put in only one area and not distributed around the complete circumference of the wheel.

A balance is poised if it is set in motion and comes to rest without reversing direction. If it reverses direction (rocks back and forth), you wait until it stops, then locate the screw nearest the bottom (heavy spot). Remove some mass from that screw and try it again. Once the balance is poised and you are timing the watch, you can reduce weight from the balance by removing the identical amount of weight from opposing screws. The balance should remain poised if the identical amount was removed from each screw.

Hope I didn't confuse anyone other than myself!