I got this clock from a flea market, Rodgers, in Rodger, OH. I think I paid $7 for it in a broken condition.
When plugged in, it still hummed, giving me hope that it was still repairable. After opening, it looks like this magnetic flywheel has become deformed, or some other problem, and it doesn’t spin freely. Some googling shows these are actually pretty neat motors- they are single phase, synchronous motors. So, the AC waveform from the wall into an electromagnet creates the dipole necessary for driving the flywheel forward, no transformer or phase regulator needed. This is nice and convenient, since mains is 60Hz, the rest of the motor is just a 60:1 and then another 60:1 gear reduction, so that the motor is making 1 rotation per minute, advancing the dials.
If we can replace the flywheel, and the motor has enough power to give it the correct RPM for the main spindle to reach 1 RPM, it’ll be good as new!
The flywheel is made from a magnetic ring in a non-magnetic cup. The cup on mine was damaged, so I just dug the magnetic ring out, and tried to make some replacement holder. All it needs to do is fit the motor spindle, fit the ring, and weigh about the same as the original. I used wood for this, since it’s easier to machine, but I had to cut out a lot of material for weight reduction.
After many, many failed prototypes, this one worked long enough for me to test my hypothesis. This was made by first cutting holes to reduce weight, then using Forstner bits to cut down the center of the wheel, and using a hole saw to cut the outer portion. This resulted in a wheel with a cap-like shape, necessary for mounting the ferrous strip in proximity to the poles of the motor. Too small, and the rim will stick to the motor, too far and the metal strip will not interact with the magnetic field from the motor. In addition, mounting the flywheel has become a puzzle in itself. Pictured is a rubber seal, but I ended up friction fitting a dowel for the final design.
It works! But, a bit slow. Removing or using a different material should help this. The prototype was built with some type of MDF. A better, lighter material was cedar. I had a lot left over from groove and tongue floor samples when we redid our floors. It’s a good thing, too, because cedar is so brittle and the parts were so small, I ended up cracking most of them while making them.
I didn’t really like the original case, even though it was in fairly good condition. I decided to build the rest of the case out of cedar, since that was what I ended up building the flywheel from (a very light wood). I thought the mix of metal and wood created an interesting aesthetic. This was also my first time using tung oil for finishing a wood project, it gives a very nice finish without any sort of tack or stickiness when touching it after it cures/absorbs.
It seems like these sorts of clock mechanisms were fairly popular back in the day. I have several that use this sort of synchronous motor as the driving clock signal, and many flip clocks also use this. The problem with these motors is that they usually do not have an external flywheel, and it will be inside an enclosure, which is typically hermetically sealed. Even if the flywheel is outside, if the oil inside the motor gums up after ages, it will not run. There are some tutorials to remedy this, but they usually involve heating the unit and then sticking it in a vacuum chamber submersed with oil. I’m not sure if that work is worth the effort, but I’m glad all mine needed was some woodworking.