Bergeron bushing cheat sheet

[Jmiod]

What is “k” column
There are two B columns

 

[Willie X]

The charts can be very confusing but they do make sense with enough study.

Both major companies sell bushings made for each of their reamers. This establishes the bushings OD. Then each of those groups are divided into two other groups by Height and ID (bore).

It's fun (and looks better) to try and pick one bushing group for all of the necessary bushings a clock may need. But often your will need two ODs but rarely three ...

Examples: A Regula 25 can always be fully rebushed using only #2 KWM bushings. Unless it needs a bushing at one or more of chain wheels. Those will require a #3 bushing. Most American clock can usually be fully rebushed using only #3 bushings. The Bergeron system can be used in a similar manner.

You will need to study about any letters associated with the bushing numbers. Some don't mean anything important, some indicate the metal used, etc.

Good luck & bush on ... Willie X

 

[Jmiod]

The charts can be very confusing but they do make sense with enough study.

Both major companies sell bushings made for each of their reamers. This establishes the bushings OD. Then each of those groups are divided into two other groups by Height and ID (bore).

It's fun (and looks better) to try and pick one bushing group for all of the necessary bushings a clock may need. But often your will need two ODs but rarely three ...

Examples: A Regula 25 can always be fully rebushed using only #2 KWM bushings. Unless it needs a bushing at one or more of chain wheels. Those will require a #3 bushing. Most American clock can usually be fully rebushed using only #3 bushings. The Bergeron system can be used in a similar manner.

You will need to study about any letters associated with the bushing numbers. Some don't mean anything important, some indicate the metal used, etc.

Good luck & bush on ... Willie X

 

[Jmiod]

Thanks Willie that makes sense because I do need #3 bushings for the chain wheels on the Urgos movement that was unlucky enough to be my current patient. And I need #2 for the other 14. My confusion is concerning the Bergeron chart has a b column on the left with what looks like bushing identification numbers and the other b column looks like I.d. Measurement is that correct? The K is what the metal used? Or am I missing the target completely.
Then when you broach is it ok to broach from one side or the other or both. If you broach from both the optimum center point will be the convergence of both tapered holes. That thin hole tapered intersection will be a thin bearing line. So , pardon my lack of experience, but one sided broaching should leave more material for wear in the I.D. Or is that not important. So can one method have an adverse effect on oil retention and wear patterns.
I am trying to weigh different broach techniques before my final test run.
How do you know when to stop broaching, I read about two turns then try test pivot insertion. Some say wobble is enough some say you should temporary install other side to spin and broach as necessary. Well I know I will develop what works for me in the process but where to start is my question with so many different opinions. Am I overthinking this because my thought process tells me the broaching is extremely important when doing so many on a movement so they all work in union.
Can polishing be done by hand? I read 3600 micro cloth and 2400 twisting by hand. Well I looked a Little I saw stones, Emery and other polishing with lathes but I don’t have the lathe luxury.
Thanks
James

 

[Willie X]

Most refer to KWM reamers as: #2, #3 and #4, etc. Bergeon reamers are usually referred to with a size measured in millimeters like: 2.47mm, 2.97mm, 3.47mm, 3.97mm, and 4.47mm.

This is the common way to talk about reamers from the two major companies but you could just use the company name and the x.xx mm size for all, that will work.

The above listed three KWM and five Bergeon reamers are the most used in my shop and span about the same range, in size, although the Bergeon bushings are bigger for the same pivot size.

If you ordered the single #3 KWM reamer and the specific 6 sizes of bushings mentioned earlier, this would help you see how everything works.

Most use the 5 sided broaches from one side and then the other. I know you are picturing a big hump in the center but that "hump" is only about .00015" high.

A well fitted pivot, in the assembled movement, should have easily observable (with low magnification) side movement, oil helps you see this. The oil jumps around a bit if the clearance is there. The arbors end play should be easily observable with normal eyesight and there should be a very small chamfer on the inside edge of all new bushings.

Take all the time you need fitting and testing every bushing. And, FYI ... nearly all new comers fit their bushings to tight. If it won't rattle, it won't run.

Willie X

 

[Schatznut]

The great Willie X says, "Keep calm and bush on."