Lift angle might be one of those horological terms you ignore. Frankly, if you don’t want anything to do with the technical aspect of watches, I don’t blame you.
But it’s not merely a hollow phrase. You never know when it might come in handy even if it’s just to impress a fellow collector over a couple of beers.
In this article, I’ll explain what the lift angle is and why it’s important.
What is it?
The balance wheel swings clockwise and counterclockwise. Each one of those swings is called a “beat.”
In the middle of a clockwise swing and a counterclockwise swing, the impulse pin enters the crown of the pallet fork.
This movement causes the pallet fork to snap to the other position, and then the impulse pin is released.
At the end of the swing, the impulse pin comes back and enters the crown of the pallet fork from the other side, and so on.
The angle in degrees between the entry and the release of the impulse pin is called the lift angle.
Why is it important?
The lift angle is necessary to calculate the amplitude.
The watch timing machine “listens” to the sounds of the movement. Every tick of a watch is made up of three different pulses.
The first noise occurs when the impulse pin comes in contact with the horn of the pallet fork. The second noise occurs when the pallet exit stone separates from the escape wheel. The third noise occurs when the escape wheel connects with the entry pallet stone.
The formula to calculate the amplitude is as follows:
(3600 x lift angle) : (time between the first and third noise in seconds x pi x beat of the watch per hour).
The lift angle is 52 degrees, the beat rate of the watch is 28,800, and the time between the first and the third noise is 0.007 sec.
(3600 x 52) = 187,200
(0.007 x 3.14 x 28,800) = 633
The amplitude = 187,200 : 633 = 296 degrees.
What if you don’t know the lift angle?
Look it up
There are several websites with lists of known lift angles. All you have to do is check if your movement is on there.
The guys at Watch Guy have the biggest and most up-to-date list of lift angles out there. There’s a good chance your movement is on there.
Figure it out
You can figure out the lift angle if you already know the amplitude.
Mark one of the balance arms, so you know its position at rest. Then, slowly increase the power in the mainspring with one click of the crown at a time until you see that the balance wheel has an amplitude of 180 degrees.
Place your watch on the timing machine and adjust the lift angle until it shows an amplitude of 180 degrees.
This is a video that explains it in more detail.
Use the default of 52 degrees
The simplest (and laziest) way is to use the default setting of 52 degrees. Most watches have a lift angle between 48 and 54 degrees, so 52 degrees is virtually in the middle.
As you can see in the video above, it doesn’t matter that much if you’re off by 1 or 2 degrees. A watch that shows an amplitude of 300 degrees in the default setting will still have a good amplitude with a slightly different lift angle.
However, some of the vintage Valjoux calibers and the Venus 188, for example, have a lift angle of 42 degrees. If you measure the Venus 188 on the watch timing machine with the default setting, the actual amplitude will be about 50 degrees lower.
So, it’s a halfway decent option for most watches, but it doesn’t work all the time. Also, if you think about it, mechanical watches are an example of craftsmanship and accuracy, so I believe you should always try to be as precise as possible.
Do you have any more tips to look up or calculate the lift angle? Let me know in the comments below.
10 thoughts on “Watch Talk: What’s the Lift Angle of a Watch?”
Can the 0.007 being obtained from the 28800 bph?
The formula isn’t quite correct. If we say t = time between the first and third noise in seconds, then your formula is: L.A. ÷ (t × π × B.P.H./3600). More accurately it should be: L.A. ÷ sin(t × π × B.P.H./3600). For small values of x, sin(x) is approximately x, so the results aren’t that different.
The differences are negligible so it makes it unnecessarily complicated.
I’m working on a project quite linked to that, do you think that i could design a pallet fork with 100° angle of amplitude ?
I’m not sure, but it sounds very difficult. The distance between the two banking pins would be huge, for example.
3600 is simply the number of seconds in i hour, and is a requirement in the formula to calculate the beat rate, and thus the amplitude.
Beats per hour. 60 sec x 60 mins (1 hr) = 3600 sec
Thanks, David. I appreciate it.
In the formula to derive the lift angle I’m confused as to where the 3600 number comes from.
The formula is to calculate the amplitude with the help of the beat rate. 3600 is just part of the formula.
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