Drilling and sanding

The next logical step in the clock is to drill holes for all the arbors and the like.  For large-ish wheels, they can be comfortably held in the lathe chuck, like so.

For the pinions, I was concerned both with getting a hole that was truly axial and with not damaging the pinion leaves.  I remembered (somewhere) reading about cutting a recess in a wax chuck to receive the outer diameter of a wheel.  Once cut, the wheel would be set into this recess and the center could be drilled correctly with certainty.  This seemed like a good idea, so I chucked a piece of scrap pine in the lathe chuck and bored a recess to receive each pinion.  I made sure that the recess wasn't too deep, so that I would be able to grip the pinion with my fingers to remove it.  I cut aggressively with the boring tool first, and then when I got close, cut in 0.0025" increments until a snug fit.  Here is one pinion fit into the recess.

Here is another view as drilling is in progress.  I gave myself practice striking centers with the graver, which was much more efficient than using a center drill.

I used three drills, starting from 1/16" to 1/8" to ensure that I didn't have much tearout from any pinion or wheel.

The resulting pinion holes were indeed dead on center.  Since the arbors are 1/8" exactly, I broached the holes slightly larger to give a smooth, low-friction fit.

Emboldened by my success, I used a wobble stick and lathe faceplate to drill the precise holes on the escapement detent and hour rack.  This turned out to be less harrowing than drilling by hand, and ensured that no parts got damaged!

After this, I sanded off the paper, using grits up to 320 and removed the dust with a rag dampened with mineral spirits.  I think I really only needed to go to 220, though.

Trying all the parts on the depthing tool indicated that the gears run very smoothly.  All the time I spent sanding paid off!  But the hour rack had a design flaw.  The teeth of the ratchet pinion (right) foul on the rack teeth (left).

So to fix this, I cut and sanded the hour rack teeth to allow the pinion to run smoothly, which wasn't too hard.

Pins and slip-it

Now that the clock "runs," I've been tuning it so that it runs well.  The largest apparent problem was that that the anchor slipped on its arbor.  This meant that sometimes the clock would run with an even beat, and then lose this...  So to fix the problem, I made a small pin, like the one shown below:

In the end, the pin shown here didn't grip well, so I turned a second one that was tapered.  Then, with the anchor in place, I drilled through the anchor into its arbor and gently hammered the pin in place.

This helped with keeping the beat even, but the clock still was stopping abruptly.  After talking with my father, we settled on lubricating the teeth.  Nearly all wooden clock enthusiasts argue strongly against such a move, most wood lubricants or finishes turn hopelessly gummy and become hard to remove.  However, one caught our attention: slipit.  They sell two kinds, a wood-working kind (without silicone) and a "mechanics" kind (with silicone).  The reviews indicate that the kind without silicone doesn't work well, but the kind WITH silicone seems to work better.

So we settled on the stuff with silicone, and I applied it to all gear teeth with a small paintbrush.  After putting on a frightfully large weight (9 lb 8 oz), the clock has worked absolutely smoothly since!  Amazing!

Now, I did notice something odd.  Although the minute hand seems to run at about half speed, the hour hand runs at the right speed.  Weird.  I guess I made TWO gear ratio calculation errors...

Motion work

The motion work is mounted on the front plate, and consists of four gears.  One is attached to the center wheel arbor, two on an offset arbor, and the hour wheel mounted coaxially with the center wheel arbor.  As described before, the motion work includes four gears giving a ratio of 1/12:

• Center pinion: 6 teeth (rotates once per hour)
• Offset wheel: 18 teeth
• Offset pinion: 8 teeth
• Hour wheel: 16 (rotates twice per day)

Here are the four gears:

The offset wheel and pinion are glued together.  To keep their centers aligned, I passed a steel rod through their common centers before clamping.

The center pinion hole was cut slightly smaller than the center arbor.  This allowed me to slowly enlarge it with a round needle file until it was a snug friction fit over the arbor.

The offset wheel has an arbor cut out of 1/8" steel rod with rounded ends.  To set the arbor location, I applied a small amount of chalk to the end, and manually depthed the wheel.

Since the offset wheel is solid (no cutouts), if I don't like the depthing, it's easy to move without making an obvious blemish.

Next, I marked out the hands on pieces of 1/4" birch plywood.  I opted for simple hands rather than something more elaborate.

Then, I cut the hands out with the scroll saw and finished shaping them with a file.  Notice that I predrilled the center holes slightly smaller than the arbors, but then made a cut on the rear of the hand to allow it to grip the arbor.

Here is the hour hand mounted on its hour wheel.  The minute hand is mounted on the end of the center shaft and holds the motion work in place.