Bushings, revisited. Can brass bushings help with internal friction problems? This information below pertains not just to the Mystery Box, but to all of my clock plans as well:
Builder Ken writes:
"Good morning. After recovering from a back injury that delayed work on my Mystery Box, I just finished assembling the gear train. I think it has a lot of friction in it and was wondering if it would be a good idea to put brass sleeves over the axles, eliminating the wood-on-brass rubbing. I also wondered if painting the faces of the gears with melted candle wax would help.
On the other hand, gear S3 turns about 30 times on one winding so I may be worried about nothing. Any opinions would be appreciated.
Ken"
Clayton answers: "Aloha Ken, Yes, you have a bit too much internal friction in your Mystery Box train. My S3, which is the wheel that drives the Mystery Arm, will return the Lever Arm to the locked position 49 times on a full wind. You might be able to decrease the internal friction by doing a little 'coloring'. A color coordinated Crayon works well to reach in between the tooth surfaces, and is less clogging than candle wax. The spring for the Mystery Box is powerful enough to overcome a lot of internal friction, but adding paraffin to the mating surfaces of the teeth can only help as long as not too much is used. Too much paraffin can clog the dedendums (troughs) between the teeth.
Read over the section on "Depthing" in my FAQ's. That depthing process will help with any internal friction problems you may have in any wooden gear project.
I don't know why it is such a common misconception that brass bushings decrease internal friction. If they did, my designs would have them.
Brass bushings actually INCREASE internal friction. Read over my blog. I have blogged on just this topic and give some measurements you might find interesting.
If the mechanism has a very solid frame, such as is in the Mystery Box, one would probably notice little difference with the bushings. However, if there is any sag in a clock frame that has bushings, the internal friction between the arbor and the bushing becomes too great, and the clearances so small that nearly any amount of sag will cause the clock to stop. There's no 'wiggle' room for the arbors running inside bushings.
I did an experiment with my Genesis, which is a Uniframe clock. The wheels of a uniframe clock run on arbors protruding from the back frame. There is no front frame, so frame sag is not an issue. I made one Genesis with brass bushings inside each of the wheels, and one Genesis with no bushings in the wheels, only holes drilled in the wooden centers of each wheel. The difference was dramatic in the amount of drive weight required. Even eliminating the "sag factor" the bushed wheeled Genesis clock took more drive weight to run it!
Also when you have metal bushings on metal arbors, lubrication is required. NO LUBE is required with metal on wood, although you can safely add a little paraffin into the arbor holes.
My Number Six has been running daily, faithfully, without a single problem, and without lubrication of any kind (because it has no bushings!) for almost nine years.
Let me know how the color coordinated Crayon trick works for improving the number of turns you get from your S3.
Aloha. Clayton"
