numbers of teeth and leaves?

Hi,

Would someone happen to know the numbers of teeth and leaves on the wheels of a typical gear train as the one shown?

Thanks,

KCCnumbers of teeth and leaves?

Re: numbers of teeth and leaves?
05/05/2008 - 16:45

Hi KCC,

A typical 2.5 Hz (18,000 vph) pocket watch would be:

Center Wheel - 80 teeth/12 leaves

Third Wheel - 60 teeth/10 leaves

Fourth Wheel - 60 teeth/ 8 leaves

Escape wheel - 15 teeth/6 leaves

A few points to keep in mind:  When determining the train count there needs to be a gear that rotates once an hour and, if seconds are to be indicated, a gear that rotates once a minute.  Also, the higher the teeth to leaves ratio the better, as it reduces friction improving the transmission of power.  As is the case with matters in watchmaking, there is a balancing act between the theoretical and practical.  The train needs to be caluculated for a given vph and having the gears rotating at the correct speeds (for example, a gear rotating once an hour, etc.) and the teeth and leaves need to be strong enough, so the diameter of the wheel blank and pinion blank can only yield "x" number of teeth and leaves reliably.

Cheers,

Curtis

thanks Curtis, good to have a watchmaker in the house :-) (nt)
05/05/2008 - 17:32

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Re: Re: numbers of teeth and leaves?
05/06/2008 - 02:46

Hi Curtis,

So, if I understand your example correctly, then:

The excapement wheel will make 20 rev.s per min or 1 rev per 3 seconds

The fourth wheel will make 2 revs per min or 1 rev every 30 sec

The third wheel will make 4/15 of a rev per min or 1 rev every 3.75 min

and the center wheel will make 1/30 of a rev. per min or 1 rev every 30 min.

If this is correct, then there must be some other gears to get the minutes and hours?  Could you tell me the ratios on the extra ones.

Thanks much for your time.

KCC

Re: Re: Re: numbers of teeth and leaves?
05/06/2008 - 17:36

Hi KCC,

The center wheel revolves once an hour, the third wheel revolves once every 7.5 minutes, the fourth wheel revolves once every minute, the escape wheel revolves once every 6 seconds. 

Except in true regulators, which we've never seen in watchmaking, you need a form of reduction gearing to indicate the time.  So, under the dial, we have the motion work:  the cannon pinion, hour wheel and minute wheel.  The cannon pinion (14 leaves) is fitted on the center wheel arbor, which revolves once an hour, so the cannon pinion revolves once an hour.  The cannon pinion leaves engage the teeth of the minute wheel (42 teeth).  The minute wheel nut/pinion (12 leaves) engages with the hour wheel (48 teeth), which loosely fits over the cannon pinion.  (this is one of the few times a pinion drives a wheel).  This arrangement is known as a two stage reduction or two stage motion work.  Multiply the teeth, multiply the leaves - divide the teeth by the leaves and you have a 12:1 ratio.  The minute hand is seated on the cannon pinion, which rotates once an hour, and the hour hand sits on the hour wheel, which rotates once in 12 hours.  The count of motion work changes to 24:1 if military time is to be indicated.  I should mention the cannon pinion has a clutching/slipping action on the center wheel arbor - this allows for enough friction for the cannon pinion to rotate with the center wheel, but enough give to allow you to change the time.

I hope this makes some sense.

Cheers,

Curtis

Thank you very much, Curtis
05/07/2008 - 02:50

This has been very informative and was exactly what I was looking for.  You have been very gracious for taking your time to explain this.  This example is good for me because my 47120 contains a 2.5 Hz movement.

Thanks again,

KCC

Re: Thank you very much, Curtis
05/07/2008 - 04:01

Hi KCC,

You're welcome!

Your watch may or may not have the same numbers (teeth and leaves), but the principles are the same.  You've got one wheel rotating once an hour (center wheel) and if the watch indicates seconds, you've got one wheel rotating once a minute (4th wheel).  The rest is playing with wheel to pinion ratios to yield 2.5 Hz (or whatever is the VPH is).

Cheers,

Curtis

Just one more question
05/07/2008 - 03:08

Hi Curtis,

I believe the one piece of info that I am still missing is the number of teeth on the main wheel.

I know lot of questions.

Thanks,

KCC

Re: Just one more question
05/07/2008 - 03:57

Hi KCC,

For this example, the barrel has 96 teeth, rotating once every 8 hours.  Something else to keep in mind, the barrel doesn't come into play for calculating the VPH. 

Cheers,

Curtis

Great!
05/07/2008 - 15:10

This has been a great discussion for my edification.  Thanks again for taking your time to define this for me.

KCC