English Bracket Clock with Verge and Crown Wheel

digitalpan

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Oct 29, 2012
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I'm working on an 18th century bracket clock with verge and crown wheel escapement.

IMG_1010.JPG

The major issue at the moment is the wear on the crown wheel teeth.

IMG_1017.JPG

The wheel is running true, but some teeth are much lower than others (seems random, they're not, for example, all on one side) - there's a difference of 0.2mm (8 thou) between the highest and lowest. Also the tooth tips are by no means flat! This causes erratic running. If I adjust the verge depth for the high teeth it will skip the lower ones; if I adjust for the low teeth the clock soon stops, caught on a high tooth.

I'm thinking I will have to skim the teeth in the lathe until they are all equal (and flat topped!) and then file the rear curved portion to reduce the tooth tip width. Gazeley, in his book Clock and Watch Escapements, suggests a flat top of 1 degree, which for this wheel is 0.3mm (about 12 thou). I'm not sure how to measure that! He also advises against disturbing the flat front of the tooth, although some of the teeth on this wheel don't seem very flat!

Perhaps I should cut a completely new wheel? Any advice or observations would be most welcome.

BTW, the clock has the name MATHEW HOLLAND LONDON engraved on the dial and back plate. There are records of a watchmaker of that name in 1758 and 1768.

Best wishes

Ian
 

Uhralt

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Sep 4, 2008
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Are you sure the crown wheel is the problem? The clock should run with a great amplitude and lots of overswing, so 0.2 mm difference in tooth length. shouldn't stop the clock. Maybe there is a loss of power somewhere in the train. How does the clock run when you put some finger pressure on one of the wheels below the crown wheel to add power?

Uhralt
 

shutterbug

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You might be able to "pull" the shorter teeth to a better height. A smooth jawed plier is needed, and it takes a little time to get the procedure right. Basically you'll line up the flat side with one side of the pliers and use it as a guide as you gently squeeze and pull upward, letting the jaws slide on the tooth surfaces. Let us know how it goes.
I see that Uhralt was typing as I was. He makes a great point. I'd still try to pull the teeth a bit anyway ;)
 

novicetimekeeper

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How many pillars does that clock have 7? Who made it/signed it?
 

digitalpan

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The clock has 5 pillars, 2 at the top, 2 half way down and 1 at the bottom in the centre. The dial and back plate (which has decorative engraving) are marked Mathew Holland London. There is a document in the National Archives featuring Mathew Holland of London, watchmaker, dated 1758.
 

claussclocks

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Check the angle on the pallets as well that they are equal. Check the degree of apart and that it is the same from center of the arbor. How much up and down play is in the crown wheel.
 

novicetimekeeper

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The clock has 5 pillars, 2 at the top, 2 half way down and 1 at the bottom in the centre. The dial and back plate (which has decorative engraving) are marked Mathew Holland London. There is a document in the National Archives featuring Mathew Holland of London, watchmaker, dated 1758.
Ah, that's why I suggested 7, I could see all 5 and assumed corner ones at the bottom.
 

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