Watch Talk: What’s the Lift Angle of a Watch?

 In FAQ

Lift angle might be one of those horological terms you simply 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 simply 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 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.

What's the lift angle of a movement?

Here you can see the impulse pin (little red dot) entering the crown of the pallet fork in a clockwise swing of the balance wheel.

 

This movement causes the pallet fork to snap to the other position and then the impulse pin is released.

What's the lift angle of a movement?

Here you can see that the pallet fork has flicked to the other position and the impulse pin is released from the pallet fork crown.

At the end of the swing, the impulse pin will start to come back and enter 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 actually 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).

For example:

The lift angle is 52 degrees, the beat 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?

1. 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.

Lepsi (a manufacturer of professional watch timing machines) has a large selection of brands and calibers with the corresponding lift angles.

The guys at Watch Guy have the largest and most up to date list of lift angles out there. There’s a good chance your movement is on there.

2. 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 in 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 healthy 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.

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