Offset Bushings??

[Leslie Mosher]

Hello everyone, I'm currently working on a Silas Hoadly time/strike movement. It came to me with several badly worn and broken Ivory Bushings. I turned some new bushings on my lathe (oak) and rebushed the clock. When I put the movement together, it would run between 2 and 6 hours then stop. I think I have narrowed the problem down to the Great Wheel and #2 Wheel (time side) with almost no engagement between the teeth of these 2 gears, and ocassionally binding, stopping the clock. Checked my bushings, they were dead center. Gear teeth are in good condition, they just seem to far apart. So, can I make a bushing with the hole "off center" and move my gears closer together? Or would I be in a worse mess?
BTW, I have a junk movement of the same clock, and the teeth on that movement mesh MUCH better. I swapped the gears to my good movement, still have the same problem, teeth barely engage. And my "good" gears have the same problem in the other (junk) movement. I've measured everything I can think of, and the measurements on the plates of both movements are virtually the same. Looking for any ideas! Thanks!

 

[bruce linde]

yes... you can do offset bushings. i have several in one wood movement clock. pivot holes should be centered just like wall clock cases should be level... only when appropriate for the situation.

 

[howtorepairpendulumclocks]

Hello. Yes, this is a much wider issue. I fully understand why you have replaced the bushings, but remember, bushing is remedial action that must be preceded by depthing. Depthing is the process of establishing the optimal centre-distance for engaging mobiles. Mobiles are designed to operate on their Pitch Circle Diameters. With wear in the bearings and wheels and pinions, both the effective Pitch Circle Diameters (PCD) and the centre distances change. Establishing the best (optimal) PCD is normally, but not always, carried out using a depthing tool. As you say, the mobiles appear too far apart. This will lead to excessive engagement before the line of centres (theoretical line between the pivots of meshing mobiles) and engaging friction or "butting" as some call it. If you can get hold of (borrow?) a depthing tool, this will help you establish Centre-Distance, and yes, you may have to make eccentric bushes or plug holes and re-drill to get it to run. In summary, always check depthing before bushing. Hope this helps.

 

[Jim DuBois]

Many woodworks clock wheels go well out of round due to cross gain shrinkage of the wood as it drys out. I have seen some of these wheels out of round by 1/8"-3/16" fairly often. That makes depthing/re-depthing a bit difficult. Sometimes replacement wheels need to be fitted in order to run properly. Measuring all the wheels in the train with the grain and across grain should quickly tell you if that is your problem. I suspect it is by the way.

 

[howtorepairpendulumclocks]

That is a really good point and one I hadn't considered. The only clock with wooden wheels I worked on was a Harrison clock with "plywood" /segmented type construction ). When you replace them do you use ply?

 

[Jim DuBois]

That is a really good point and one I hadn't considered. The only clock with wooden wheels I worked on was a Harrison clock with "plywood" /segmented type construction ). When you replace them do you use ply?

Never ply in my shop on a period clock. I tend toward preservation and original style work and materials. The wheels are almost aways cherry in these production clocks. It would have originally been quarter-sawn cherry which is difficult to come by these days. But, there are hardwood sellers on fleabay and others, getting a thin stock can also be problematic but possible. Side view and some stock I use for wheels and bushings of cherry as I recommend for clockwork.

And Harrison's approach to clock building is certainly above reproach. At least 1 of his wooden works clocks is running after 300 years. His methods are not what we used 100 years later on clocks like yours, sadly.

 

[Leslie Mosher]

Ok, to close this thread out, I did use two offset bushings (one at each end of the arbor so the arbor would run "true") I repaired the problem with my gear mesh. About .020" off center. I made the bushings out of red oak. I don't have access to a clothing tool, so it was trial and error. Not the best way, but the best with the equipment I have. I made several pairs of bushings, each with about an increase of . 005", and did a lot of hand fitting with the bushings until I was happy with the fit. Arbor sets level and I have good gear mesh on each end of the arbor. With my lathe, it only took me about 20 minutes to turn out about 10 different sets of bushings. I probably wouldn't recommend this type of repair, but it worked out ok. Thanks for the ideas!!