Workshop Hints
French Clocks
The British Horological Institute has archived and edited the following from e-mails sent to the Clock/Clockers mailing lists on the Internet. The information here does not necessarily indicate a method approved by the BHI, we are only publishing this digest so that others can decide for themselves whether the methods listed below will suit them.
From John Newgas, Karen Eldred, Harry Gilmore
Index
General Hints
Bushing
Pendulum Wobble
- The locking plate strike mechanism has a critical set up of teeth. Look and see if any of the pinions have one corner filed off as assembly markers before disassembly. Examine the warning mechanism with the fly brake
- The pivots will be VERY hard and thin. The pivots rarely need any attention.
- If the suspension has gone go to a surgical supply house and ask for old fashioned silk suture thread size 0 . This is almost exactly right. Ask for the ecru/undyed rather than the black sort.
- The clocks may need a bit of attention to get in beat.
- There is usually no need to bush at all.
- Do NOT under any conditions use regular clock bushes which are way to big. Get special French Clock Bouchons. These have a smaller o.d for a given i.d. They have a nick round the centre to allow them to be broken off. Alternatively get clock bushes made for French clocks
- Enlarge the hole with a broach from the inside. Insert the bouchon from inside the plate and push/hammer until the inner surface is flush. The bouchon size is chosen to fit the pinion only. Enlarge the hole to fit the bouchon. Do not attempt to enlarge/polish the bouchon hole.
- Flatten the bouchon on the inside of the plate with bulls foot file to get a flush finish, then polish with a scotch stone taking care not to get abrasive in the bushing.
- Break of the bouchon on the outside and reduce it to the correct height with a cutter with centre guide to fit in the pivot whole. Finish with a disk cutter which will reform the oil sink and the whole job will be done and invisible.
Causes of Pendulum wobble
- Can be caused by unevenness in the load on the two parts of the suspension spring below the adjusting kerb. This will happen if the spring is not hanging "straight", i.e., not at a right angle to the lower edge of the kerb, or if the bottom spring attachment is not "straight-on" (these are usually held by a single rivet, and CAN get rotated slightly).
- Another possibility is that the pin at the bottom of the spring is not straight across, and therefore the pendulum is hanging predominantly by one side of the hook.
- Also, is the hook straight on the pendulum?
- You must first be satisfied that the suspension spring element(s) is a slip-fit in the jaws of the Brocot (or Vallet) adjuster -- the adjuster may need to be dismantled to achieve this
- The pin through the top is tight in the support but NOT tight in the brass top of the suspension.
- This is all to ensure that the spring is free to move forwards and backwards without binding.
- Then the hook at the top of the pendulum should be a neat, but not *too* tight fit on the bottom brass piece of the suspension.
- A buckled (even slightly) suspension spring and/or a crutch that is not normal (at right angles) to the back plate, assuming that the backplate is reasonably vertical.
- The only other thing to look for (but not a cause of wobble) is that the crutch fork also be a neat but not tight fit, and lightly lubricated.
