Thursday, January 31, 2008

How to attach the hands

A lot of confusion can crop up with hands that aren't cooperating. For example, sometimes it may look as if you clock has stopped but in reality the hands just aren't moving because they are too loose on the shaft. Sometimes one hand might be turning normaly, while the other stays still. Sometimes your clock might not be chiming or striking or calling when it's supposed to, but does it just before or just after the hour.

If any of these things apply to you, don't worry, your clock isn't broken, it just fell out of adjustment.

Clock hands are purposefully kept finger-tight or friction-fit so that they can be easily adjusted. Many clocks have very different methods for holding hands on. Most modern clocks follow some variation of the cuckoo clock model (discussed here in great detail) but there are a few that still follow the traditional example of antique clocks.

The Tapered Pin is, to the clockmaker, as the nail is to the carpenter. This is an elegant, slender pin with a very slight taper. It's purpose is to go through a hole on the end of a shaft and its taper allows friction to hold it in place. The hole is often on the end of a rod with a locking washer between the tapered pin and the object it is holding.

Many things on a clock are held together with the tapered pin method. Dials are held on, movement plates are held together, and of course hands are held on with tapered pins.

In the picture below you can see the shafts on which the hour and minute hand fit. The larger shaft (which is tapered) is called the Hour Hand Cannon. This rotates slowly around the smaller shaft which is circumscribes. The smaller shaft is the Minute Hand Shaft. This is often (but not always) squared - either the whole length or just at the end.

In the picture above, you can also see where the tapered pin fits in the end hole.

In the picture below, you can see how the hour hand fits on the Hour Hand Cannon. In this example, the minute hand assembly has been left out for clarity. As you can see, the hour hand slides back: over the cannon. The taper of the Hour Hand Cannon holds the hour hand in place.

If your hour hand is loose, simply slide it back further on the tapered cannon in the direction of the arrows.

Below is a picture of the minute hand assemply and tapered pin. Here, the hour hand assembly has been left out.

In this example, the minute hand has a squre hole that fits directly onto a square shaft. This is not always the case. Sometimes the minute hand has a round hole which fits over a square washer or bushing - more similar to the cuckoo clock example here. What is important in the example above is the way that the locking washer pictured keeps tension on the minute hand. In this drawing considerable space is shown so that you can distinguish between the parts but actually there should be no space between the minute hand, the locking washer, and the tapered pin.

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