Thread sizes and pitches on early English clocks

NigelW

Registered User
Jan 2, 2015
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Were there any standard thread pitches on old English clocks (early 18th C)? I have been trying to work out the size and pitches of those missing from mine by threading some peg wood into the holes. Most common seems to be 32 tpi, with a 1/8" diameter, but there are some which seem to be 60 tpi too with a diameter of about 0.075 inches.

My Myford can certainly cut a 32 tpi and, although the configuration is not listed on the table inside the cover, I am pretty sure I will have enough change gears to set it up for 60.
 

Troy Livingston

NAWCC Member
Aug 28, 2006
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Sorry, no standards. This is why I buy old screwplates whenever I can get them reasonably. If your part is thin you can get away with more error in pitch but for a deep threaded hole you need to be very close. Some would say to retap for a modern thread but this isn't the way I was raised, the rule is to make the repair part fit the clock and not the other way around. If possible I measure another screw on the same movement that has the correct thread and work from that. When this isn't possible then I try the pegwood. You are on the right track but modern thread charts are not going to be of help here.
 

NigelW

Registered User
Jan 2, 2015
455
44
28
London and Kent
Country
Sorry, no standards. This is why I buy old screwplates whenever I can get them reasonably. If your part is thin you can get away with more error in pitch but for a deep threaded hole you need to be very close. Some would say to retap for a modern thread but this isn't the way I was raised, the rule is to make the repair part fit the clock and not the other way around. If possible I measure another screw on the same movement that has the correct thread and work from that. When this isn't possible then I try the pegwood. You are on the right track but modern thread charts are not going to be of help here.
Thanks for your reply, which is the answer I rather expected. I won't be recutting any threads unless absolutely necessary. My policy is to touch as little of the original work as possible. I will need to reopen two or three holes in the back plate which were plugged when it was converted from verge to anchor in order to convert it back again but that should be it. A question I will need to address later is whether or not to plug unneeded holes such as those drilled for the anchor conversion. I am currently in two minds about this.
 

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