Sunday, February 24, 2013

Depthing the wheels

Once you have cut out your wheels (big gears) and pinions (little gears) the next step is to "depth" the wheels. This is clockmacker-speak for "getting the gears to mesh correctly." As cut and sanded, the wheels and pinions will almost certainly not mesh. Small errors in cutting the gears will magnify.

Now in a clock we have a huge gear reduction, possibly 3600 to one (that is the number of seconds in an hour). This huge reduction is accomplished in stages and that's why we have pinions and wheels. That is why a clock looks so complicated. Every wheel (lots of teeth) meshes with a much smaller pinion (few teeth). And we are dealing with wood, which even in its plywood incarnation is kind of recalcitrant. A clock put together in winter might not run in the summer because the change in humidity swells up the wood and the teeth jam. Brass is much more humidity-resistant and that's why we usually make wheels out of brass. We also make pinions out of steel.

But I am stuck with wood. I am not complaining! I chose the way myself. Now we have to live with it. Each wheel has a mating pinion. I'm following Mr Wilding's instructions and he as built an infinite number of clocks compared to me; this is my first clock. Anyway what Mr Wilding recommends I do.

So above I have very, very carefully drilled holes in the back "plate" (frame piece of the clock). The holes are just large enough to accomodate a finishing nail. I have cut off the head of the nail. And so begins a tedious odyssey. You spin say the pinion, the little gear at the top. At some point it will certainly jam. You look at it with a magnifying glass. If necessary with a jeweler's loupe. You determine what is wrong. In general if you can see ink lines in the gears it will jam. You carefully sand away these lines. It still may jam. You sand away some more. I use my swiss files and lady's fingernail abrasives, AKA nail files, very cheap. Let us be thankful for lady's long fingernails. So there we have one pair of wheel-pinions complete.

Very tedious. But watchmakers have the same problems, only at a much smaller scale. So I am grateful. I only have to  use a loupe occasionaly. I have a really nasty problem on the second wheel-pinion combo. Stay, as they say, tuned.

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