County Antique Clock Repairs
Friction -- where it comes from and how it stops clocks
There are no
perpetual motion machines because of two forces that can never be
completely overcome: gravity and friction. In horology, friction is
the more important because it can take many forms that gradually rob
clocks of the energy that they need to keep 'escaping'. Friction is
caused by the motion of two objects that move against each other.
This phenomenon occurs in various places in clockworks.
When clocks are cleaned and overhauled, the clockmaker removers the dry and dirty oil from the movement and applies fresh oil to combat friction and wear. The problem is that even special clock oil evaporates over time. When this happens, the oil doesn't lubricate any longer; it actually retards movement. This occurs often in the mainspring, where the oil thickens to the point where the coils of the spring no longer rub smoothly against each other. The transmission of power is thus drastically reduced and the clock will fail.
Another place where oil thickens to bad effect is in the holes of the front and back plates. Clock plates are typically made of brass. They have holes in them to accommodate the steel shafts on which the gears are mounted. The small ends of these shafts are called 'pivots'. Oil must be applied where the pivots pierce the plates. But that oil evaporates and thickens over time and it collects grit from the environment. There comes a point where the pivots no longer rotate freely in their holes. When sufficient friction occurs, the clock will stop.
The force exerted by the mainspring or the weight has to be strong enough to move all the gears. The stress on the gear shafts and pivots can be significant, and can result in the holes becoming out of round and taking an oval shape. When this occurs, the gears do not mesh correctly. As a result, friction occurs as the gear teeth rub against the pinion leaves instead of sliding along them. To remedy this condition, the clockmaker dismantles the clock and carefully enlarges the hole so that it is concentric with the original round hole. Then the clockmaker installs a 'bushing', which has the same outside diameter as the enlarged hole and an inside diameter that is the same as the original hole.
Wear can also occur on the surfaces of the pallets because of the incessant pounding the pallets receive from the escape wheel. Even though the pallets are made of steel, the brass teeth of the escape wheel manage to wear them down. There comes a point when the surfaces are so worn that the escape wheel does not travel smoothly, or that the pallets are no longer receiving sufficient impulsion to keep the pendulum swinging or the balance wheel oscillating. The clock stops. The clockmaker must polish all signs of wear from the faces of the pallets and must sometimes adjust the distance between the pallets and the escape wheel teeth.
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