I have installed a few bushings in clock movements over the past 7 years but have never bushed a clock barrel. Some clock-makers will say they bush barrels all the time but of all the barrel mainsprings I have seen this is the first that is in such poor condition. Although this is my first attempt at bushing a barrel it was largely a success.
Two years ago I bought a Jauch schoolhouse clock at auction for $50. It has a time-only movement. It is a pretty simple movement and is a great start for those of you just getting into clock repair.
German movements made in the 1970s were not always of the highest quality. They suffered from two significant issues, plated pivots and soft brass. Softer steel pivots were used to extend the life of the cutting machines and the addition of plating achieved sufficient hardness. Unfortunately, plating wears down over time and the result is a very worn pivot.
This movement does not have plated pivots. The second issue is the use of softer brass. In the case of this clock movement the steel arbour has worn the brass cap and barrel.
I installed three bushings in a previous servicing though I did not address the mainspring barrel.
Since I bought it the clock it has always run 10 minutes fast in the beginning of the 8 day cycle and 10 minutes slow at the end of the cycle. There must be something in the physics domain about barrel slop that contributes to the wacky cycle that I don’t understand but something nefarious is certainly going on. Will bushing the barrel and the barrel cap change the running characteristics of this movement? We’ll see.
A barrel of fun
To address the barrel repair I selected a #60 Bergeon bushing, the largest in a my supply of bushings.
To remove the barrel arbour from the barrel I had to remove the ratchet gear. Since I do not have a gear puller I put the barrel in a vice, positioned two pieces of wood on either side under the ratchet and gave the arbour a small tap with a nylon end of a brass hammer to remove it. Off it came.
With the barrel cap popped off and using my spring winder I removed the mainspring to permit access to the the barrel and used a collar to restrain the spring. Everything was going smoothly so far.
I positioned the barrel in my Bergeon bushing machine and using my centering bit established centre. Using an 8.47mm cutter I made a hole and installed the bushing. I peened the bushing in place, that is, I put a lip on both ends to ensure that it stays in place. Now on to the cap.
This where things did not go quite as planned. I centered the cap as best as I could on my bushing machine, drilled through the cap and installed the same size bushing however the arbour is a larger diameter than the barrel side so I used another reamer to cut away the inside of the bushing. I realized the bushing wall was becoming quite thin. To maintain a thick enough wall I decided to reduce the diameter of the arbour. Using my metal lathe and a cutter to trim the arbour I achieved a good fit. I then peened the bushing in place.
When I re-installed the barrel into the movement I discovered that I could have centered the cap better. There is a slight tilt which is evident when I installed in the movement. Will the gear properly mesh with the second wheel pinion as the barrel rotates or will it rub against the second wheel? After a few days it did not seem to be an issue.
In retrospect I should have bushed the barrel side and tested it before doing the cap side. It is all good learning!
Next time determining exact centre will result in a better outcome. This is a a cheap clock to begin with and not my best work.
In the future when asked if I have ever bushed a barrel I can say, “darned right I have”!