Printed Clocks

I came across an old video of yours (https://www.youtube.com/watch?v=jbh_vp3qcRU) when I doing some experiments on friction with various arbor sizes. You say that smaller arbors have smaller friction. I was wondering why you went with a 3mm arbor for the pendulum in SP5, as it is the place where friction (or energy loss) matters the most. Wouldn't 1.5mm have given lower energy loss and hence allowed a lower driving weight.

(Long and probably tedious details follow.)

My experiments consisted of setting up a standalone pendulum and timing how long its swing took to decay over a specific range. I did this with 1.5, 2 and 3mm arbors, and I also compared cases where the arbor was held tightly in the pendulum head and where it was loose. It was always loose in the frame. I also tried bearings versus a smooth and deburred hole of a size a little larger than the arbor. I tried to use arbors of the same material and finish in each test. It's probably a bit boring to give all the results (and they should be taken as only a sketch and not very scientific), but the broad results are:

• 1.5mm arbors ran for about 25% longer than 2mm ones.

• 2mm arbors ran about 10% longer than 3mm ones.

• when the pendulum head was tightly attached, it substantially reduced the time in the 2mm and 3mm tests.

• bearings didn't make a lot of difference, except at first with 2mm when they made things much worse.

What I take from the last two points is that using bearings and larger arbors makes the design more prone to manufacturing tolerances. In both cases when I allowed a bit more play (for the arbor in the frame in, and for the bearings in their mounting holes), I got similar timings to the case when the arbor was loose in both frame and pendulum head. It's likely that at first the arbor was over constrained, so it could find its own orientation for minimum friction.