Author Topic: Westphale escapement  (Read 7469 times)

kmuldrew

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Westphale escapement
« on: March 16, 2010, 08:04:40 PM »
Most people here are probably familiar with Wayne Westphale's clock from Fine Woodworking ca. 1986. In going through his article again, I find myself wondering if his escapement is less efficient than it ought to be. In a dead beat escapement, one would like the pivot point for the escape lever to be on the crossed tangent lines taken from the escape wheel circle at the points of contact. Westphale's design puts the pivot point 20 degrees above the tangent line. It is as if he has designed the escapement for an escape wheel with only 15 teeth rather than 30. If the pallets closed around 4 1/2 teeth rather than 2 1/2, then the original pivot point could be used and the escape lever should still fit within the clockworks. Am I figuring this correctly, or is there some aspect of Westphale's design that I'm missing? I am certainly no expert on escapements.

On another note, has anyone tried retrofitting a grasshopper to a Westphale clock? Given how far the crutch is to the side of the escape wheel, it would be difficult to stick one in without some pretty big modifications. Although perhaps it would be possible to connect directly to the pendulum pivot rather than the original crutch.

Ken Muldrew.

kmuldrew

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Re: Westphale escapement
« Reply #1 on: April 06, 2010, 08:54:10 AM »
Sorry for following up my own post, but having now tried the larger escape lever I can say that it does run with less weight than is required for the 2 tooth lever that Westphale originally used. My guess is that he adapted a 15 tooth escapement and forgot to double the number of enclosed teeth when he doubled the number of teeth on the escape wheel. If anyone decides to go this route, just be aware that the longer escape lever will have to avoid the center arbor (so one can't just scale up the pattern from Westphale's original).

Offline Rob Walker

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Re: Westphale escapement
« Reply #2 on: April 13, 2010, 09:53:11 PM »
I've just spent a few days on my CAD program designing and testing a pallet to work with a club foot escape wheel that is nearly identical to the Westphale wheel.  What I learned in regards to the pivot point is that the standard method of drawing intersecting tangent lines 90º off the division angle may work well with a 15-tooth escapement but on an escape wheel with 30-teeth and a pallet span of only a few teeth it places the pivot very close to the wheel.  It was too close for my pallet bracket design and I too had to move the pallet's pivot point further from the center of the escape wheel.  Perhaps when the pallet lever is mounted on a more traditional arbor suspended between the clock plates this distance would not be as critical.

I also noticed that Wayne used a 2.5 tooth pallet span and I was surprised by this as well.  Correct me if I'm wrong but a smaller span requires a larger crutch and pendulum amplitude and Wayne made a point in his article about keeping this amplitude small. Not being mathematically inclined I would have to draw it and simulate it to see how much of a difference Wayne's smaller span would make.

After my recent exercise in escapement mechanics (exhausting but worthwhile) I'm convinced that this is one of the more fascinating and mind numbing aspects of a mechanical clock.
« Last Edit: April 14, 2010, 05:08:09 AM by Rob Walker »
A clock that, by natural motions alone, indicates regularly equal divisions of time.

—Mateo de Alimenis Campani (1678)

kmuldrew

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Re: Westphale escapement
« Reply #3 on: April 15, 2010, 02:07:47 PM »
Here is an animation of how I think the escapement should work in the Westphale clock:

http://people.ucalgary.ca/~kmuldrew/woodworking/big_westphale.gif

The pendulum is in the wrong place, but otherwise I think this is OK.