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# Wooden Clock Bearings

### Bearings

After looking at numerous articles and papers I decided to use ball bearings.

David Lucy has a page around building his own clock, in this he notes that ball bearings are not suited to the stop-start motion of clocks and that the drag is high.

dg-chrono.de - miniature ball bearings in clocks. This article quotes a friction value for the miniature bearings, µ=.002, compared to a µ=.15 - .20 for plain pivots.

I did some simple measurements of the bearings in the pendulum. The basic bearing is a 10mm OD, 6mm ID and 3mm thick ball bearing with metal shields and filled with grease.

I held the pendulum out at 15° from upright and marked the back plain of the clock at this point, I marked again at 10° and 5° using a Wixey angle position gauge attached to the pendulum.

I then started the pendulum just beond a 15° amplitude swing and then timed it from the point it decayed from 15° to 10° and to 5°.

 Condition 15° 10° 5° Sealed Bearings 0 177s 554s Ball Bearings - no seals or grease 0 201s 688s Ball Bearings - no seals, graphite 0 167s 458s Ball Bearings - no seals, WD40 0 197s 704s

After fitting an exponential decay curve through the 3 points I then differetiated this and calculated the power being dissipated by the pendulum at an angle of swing of 5° which is around the angle the pendulum swings when the clock is running.

This gave:

• Std sealed and greased bearings = 0.054mW
• No seals and WD40 = 0.03mW

And so around half the power is dissipated with the seals removed and a very light oil used as a lubricant.

The main clock index page.

If you have made a similar clock and would like to share your experience we would love to hear from you - ed.