The Mechanical Clock Pendulum Assembly
The mechanical clock pendulum assembly does not mean just the pendulum alone. The use of the word assembly means the pendulum consists of three components and not just the pendulum. A pendulum assembly consists of the suspension spring at the top, the leader that hangs on it, and then the pendulum.
Usually mechanical clock pendulum makers are not movement makers and the two are married together by a person or place. A place such as Clockworks or Howard Miller instead of the movement manufacturer. This is interesting because it explains why there can be so many variations in pendulums for one movement. The pendulum could be a brass rod, wood stick, or metal lyre style.
Pendulum bob diameter size
To determine the bob diameter for a mechanical clock pendulum, you need to consider what looks good as well as which one won't whack the sides of the case. A good rule for the bob diameter is it needs two inches on each side to swing. So if the clock case is 12 inches wide the bob cannot be more than 10 inches. In this example we would need a 10 inch bob but these are not made.
So the choice is clear that for a 12 inch wide clock case the maximum bob size to get is 8 1/2 inches wide. If this rule did not exist and the 10 inch wide bob is run the clock may go tick, knock, tock, knock, as it hits the sides every time it swings. Eventually the clock will stop running from this resistance. Plus it is quite annoying to hear that sound!
Pendulum lengths for Mechanical Clock Pendulum Assembly
The length of the pendulum has to be correct for the gearing inside the movement. If the mechanical clock pendulum is too long the clock will be too slow. If the pendulum is too short the clock will run too fast. When a clock is too fast or slow it usually has nothing to do with the movement itself. It only has to do with the pendulum length alone and nothing else.
Pendulum top mount hook
The top hook has to hook to the leader on the movement. The leader is the part that holds the mechanical clock pendulum up in the air and it hooks to the suspension spring. Sometimes an old pendulum will not hook to the new movement the same way as it did on the old unit. However, this is not common. It may or may not need a new top hook for the pendulum.
The leader is the 3 to 7 inch long part that the mechanical clock pendulum hangs onto. The leader hangs onto the suspension spring which is on top of the movement. At the same time it will have the crutch on the back of the movement engaged with the center of the leader. The crutch is the wig wag part that is sticking out of the back of the movement.
To install the leader, remove the set screw on top of the suspension spring. With the suspension free it can hook onto the leader and be brought back up. The leader then goes onto the suspension and the crutch on the back of the movement at the same time. This assembly gets brought back up again to mount with the set screw like it was.
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