John B. Shadle, CMC
John B. Shadle, CMC
If you fix old Connecticut clocks, you've seen broken regulators. In its unhappy past, this regulator has been turned to its limit, and then turned some more, which broke the little gear train that screws the regulator up and down. This one belongs to a Sessions black mantel.
Soldering in new teeth would be difficult, since they're bent to form a bevel gear. Besides, weak replacement teeth could be stripped again in an uncertain future. So I decided to find a way to replace the pair of little cogwheels, entire.
The source of the "new" cogwheels is the pinion on the second arbor of a junked Hermle. The pinion has more teeth than the original cogwheels, but that doen't matter -- What does matter is that the pinion has approximately the same diameter as the original cogwheels. Junked pinions come in many sizes, so it's possible to find one which will fit the job. These pinions are made of free-cutting steel, so working it is easy.
First, I knocked the wheel from the pinion using a heavy V bench block and a hammer. Then, I simply sliced off the cogwheels from the pinion material with a parting tool, using my Taig Lathe. The pinion remnants appear below the parent second wheel on the left.
Before slicing cogwheels from the mother pinion, however, I drilled a hole through the pinion. The hole is a bit undersized, so I can press fit the cogwheels onto the regulator arbors.
You must disassemble the regulator to repair it. The top plate is swaged onto the regulator posts, and an attempt to tap out the posts with a punch and hammer failed. So I carefully ground away the expanded metal on the ends of the posts with my 1" belt sander. Then the posts could easily be tapped out of the end piece, using a punch and the V bench block shown above. In the photo on the left, one of the new cogwheels is already in place on the end of its shaft.
The new cogwheels are friction fitted on their arbors. Had they been a bit loose, I would have used Loctite to keep them in place. A tight friction fit is better, since it will better withstand torque applied by the key.
To reassemble the regulator, I first chamfered the outside of the holes in the end of the regulator where the posts fits through. This reveals a little protuberance on the ends of the posts which can be riveted over to hold the regulator together.
The regulator is shown reassembled on the left and in place on the clock on the right. The original cogwheels formed a bevel-gear assembly. These don't, but they work fine anyway. The fact that the new cogwheels have more teeth than the old ones just improves the smoothness of the drive. Because they are made of steel instead of brass, they should last longer.
This is a different regulator from a Waterbury black mantel. Repairing this one was a greater challenge, since the damaged cogwheel has a hub with internal threads. The original threads were of an indeterminate size, so I decided to make new parts with 2.5 mm threads -- a close match. I made both a new cogwheel and a new shaft for it to turn on.
I disassembled The frame of the regulator in the way described above. Removing the cogwheel from the frame required a different approach, since it's inserted through a hole and then swaged over a washer to keep it in place.
To remove the cogwheel from its frame, I used an ordinary round broach as a mandrel. The cog with its bracket attached is skewered onto the broach and given light taps to seat it, then the big end of the broach is put into the lathe chuck and the small, pointed end is supported by a homemade brass cone center held in the tailstock. Then I made light cuts until the cogwheel can slip away from its washer and out of the bracket.
The new cogwheel was once again turned from the pinion of a junked Hermle. I wasn't able to find an exact match for this one, but one that was close. The new cogwheel is about 0.010" smaller than the original and has less teeth. But it seems to work well anyway. Goes to show that you shouldn't expect more precision than is need by the job, and in this case a sloppy fit works almost as well as a good one. The repaired regulator appears on the right.
There is a small nut on the end of the threaded shaft which keeps the cogwheel from screwing off. I reused the orignal, although there was a mismatch with the new 2.5 mm threads. The mismatch provids the right "interference fit" to keep it on the shaft. The original driving cogwheel of this regulator was undamaged, so is not shown.
Here's another broken regulator with another problem, this one from a Seth Thomas. In this case, the regualor screw has been twisted off and a "repairer" has butt-soldered it back together. Of course, the solder joint won't screw through the threaded hole in the movable part of the regulator. The only option is to make a new screw.
The old screw is about .083" in diamter, which is probably some unknown wire gauge, but not duplicated among my materials. So I decided to make the new screw from 3/32" (.093") steel welding rod, which is about .010" larger than the original.
The threads on the old screw are also indeterminate, so I decided to make threads of 2.5 mm. (.098"), which is a few thou larger than 3/32". All ideal.
The cog is riveted onto the old screw, so removing it was only a matter of removing a bit of expanded steel. The cog has a square hole which mates with a square on the end of the screw, so the end of the new screw must be made square.
I squared the end by first drilling a little block of hardwood with a hole just under 3/32", then I broached the hole to make a snug fit to the new screw. Then I used the block as an "index" to grind the four sides onto the new screw, using my 1" belt sander. I took my time, removing only small amounts, since the faces must be about equal all the way around, or the cog won't sit correctly when it's swaged back on. A filing rest on a watchmakers lathe would have also served to make the square, and might have been better.
I chucked the new screw in my drill-driver to make the 2.5 mm threads. The driver has variable speed, plenty of torque and is reversable. I put a drop of oil on the screw to facilitate cutting the threads.
The new screw with cog riveted back on is shown on the right. Since the unthreaded holes in the old regulator parts are smaller than the new screw, I opened them a bit with a broach. I made a little cut on the upper end of the screw to fit into the bracket at the top of the regulator.
The threaded hole in the movable part of the regulator must be re-threaded to 2.5 mm. I didn't ream or drill out the old hole -- just let the tap make new threads in the brass. (The tap is .015" over the size of the old threaded hole.)
The repaired regulator shown re-installed in the clock on the right.
