Methods for Gear Attachments
Roy asked if a gear puller was used to separate the gears fro m the arbors. My answer grew to warrant it’s own post.
The gears are are attached to the arbors in a number of different ways, depending on the gear and the role that each plays.
The gear which corresponds to the minutes of the clock, uses a tri-legged pressure plate (one leg of which is seen touching the 2nd gear back) so it is linked only by friction. This allows it to slip (with difficulty) so the time can be adjusted without disengaging the gear train. It also means if the hands of the large tower faces were to freeze up, the clock would not jam.
The main drive gear (with the weight drum) uses a large cotter pin and a collar. I’m not convinced this is original. I will be investigating to see what was used in the late 19th century.
The birdcage gear and the escapement air-brake used small steel pins. I’m pretty sure these are original as I’ve seen them used in smaller clocks from the same period.
The difficult part is there are two gears that were “pressed” onto the arbors and another two that were sweated and lead soldered in place. I have not yet decided if I can get the soldered gears off. If I do go this route, it will only after considered the stresses these gears are under, because I would prefer to pin them back to the arbor rather than solder them back.
March 26th, 2007 at 21:53
Thanks Glen…
March 27th, 2007 at 07:36
actually - “thank you”. Great questions and I’m glad I took the time to really notice the variations the builders of the clock took and “why”.
June 12th, 2007 at 15:19
What has been referred to as an air-brake or fan-fly is actually not significantly slowed-down by air resistance. It doesn’t achieve enough velocity for that to be a major factor. The purpose of it is to “dispose of” the inertia (or excess energy) which is in the escapement arbor (on which it is fitted) when that arbor is stopped in its forward motion by the locking of the escapement. I had trouble convincing people of this until I found, in museum collections, several clock movements by Bond (Boston, mid-19th century)which had gravity escapements and which had small-diameter but heavy “flywheels” instead of large fan-shaped flies. The key (whether it be shaped as a fan or as a small heavy flywheel) is that it is *friction-mounted* on its shaft. and runs forward (typically 90 degrees or so) once the escapement locks; thus converting the left-over kinetic energy to heat.
June 12th, 2007 at 15:50
Hi Alan - yes, as I learned more about the clock, I learned the correct “language”. the object which looks like an air-brake is correctly called a “fly” in my later posts. I’ve also learned, in this particular case, the “fly” serves one primary purpose and one secondary purpose. As you point out, its primary purpose is to keep the legs of the escapement from bouncing when they reach the stops. The inertia in the fly causes it to rotate forward (in my clock it only rotates about 5 or 10 degrees) when the leg hits the stop, and thus keeps the leg in stable contact. The “fly” does has another purpose - though it should never come into play. The “fly” does act as an air-brake in the unfortunately case that the escapement legs jam or get stuck in their extended position. In this rare case, the “fly” will prevent the clock from becoming a run-away and crashing. A flywheel would not provide the added function.
thanks for the background and setting the record.