Cates Clock Repair

Pivot hole repair is the most common type of repair necessary in getting a clock up and running again. The pivot hole must be repaired when it becomes deformed and the pivot hole center has been moved away from its original place. This occurs because of the friction and pushing effort of the gears in each clock train.

I have referred to the gears as being "trains". A gear train is simply those gears that are inline with one another, from the first gear containing the spring, to the last gear. All these gears combine to form the gear train. If the pivot center of one gear is moved either away from, or towards the next gear in the train, then power is no longer distributed properly and the clock is not fuctioning as designed. Evenutally, this movement of the pivot hole center will cause the gears to either push so close together that they cannot turn anymore, or they will not be supplied the proper power along the train to make it function.

So how does this happen? You must first understand what makes up the gears in the train. Gears are made of two types of metal; Brass, which is a soft metal, and harden steel, which as the name implies, is very hard. The gear teeth are made of the soft brass and the gear arbors and pivots are made of harden steel. The gears turn because of the force applied to them by another gear.This force is not a circular applied force, but a straight forward force. And since the gear cannot move sideways because it is in a pivot hole, the gear must turn in the opposite direction from where the force was applied. The gear must follow the path of least resistance. So although you can watch a gear turn and it appears to be having a fun time with the gear next to it, the force being applied is actually pushing the gear away.

We know that the gear arbor is made of harden steel and that it sits in a pivot hole of soft brass. Now because the gear behind it is pushing the gear in front of it away, which results in making the next gear turn, this force is also pushing the gear through the brass plate. Over time, this pushing effect of the steel arbor through the brass plate causes the pivot hole to lenghten and form an egg shape, instead of the round pivot hole shape it should be. With the pivot hole now being egg shaped, the center point of the pivot hole is now moved and the arbor and gear position have changed. To repair the clock and put it back in working order, we most re-establish the pivot hole to its original position.

This is done through filing the brass plate, using a reamer to establish a perfectly round hole, and inserting a new brass bushing of the proper size to fit the gear. Once all this is done, and if it is done correctly, the gear train will function as it did when it was brand new.

To see what a deformed pivot hole looks like, click on the picture below. This gear is being force down and to the left. The resulting force has pushed the gear through the brass plate, changing the original center of the pivot hole.