fly arbor with broken pivot

[namonllor1953]

yeah Chris,
I’m one of those who believes there’s always a solution, just got to figure it out.

[bernie weishapl]

I just know the one I made with the steel that Bob suggested rounded out on a French clock I worked on about a year ago. So I used my carbide graver. I guess I hadn’t thought of maybe finding some carbide that a person could make one out of. I have a diamond wheel on my grinder that may work to sharpen it. I think I will look into and see what I can find. I just didn’t pursue it because a graver worked. The tool works well on American time & strike and on most modern clock arbors because the steel is no hard. Not if Jan was to anneal it that may work also but then would have to harden it again.

[arutha]

Hey Bernie,
speaking of hard french steel pivots, Daryn has just ordered some carbide in the same dimensions as a standard pivot burnisher. We will prepare them on a diamond plate and try them out on some french pivots, some of the old English longcase clocks had very hard pivots, hard enough to destroy a pivot file after a couple of goes. I will keep you posted if it works out well.

Jan,
I am more than happy to do the re-pivot for you, just ask Bob to send you my e-mail address and I will send you my address.
Paul.

[gerene]

Thanks Paul I will send you the arbor. Like Chris said, I would probably spoil it being stressed trying not to break it 😳
So, Bob, can you please send me Paul’s email?

Thanks, I owe you!

Jan

[Bob Tascione]

Hi Jan,
Just sent it so should be in your box now.
Adios,
Bob

[gerene]

Thanks Bob. I will send an email to Paul straight away.

[bernie weishapl]

Paul will be interested to see how those work out. Let me know.

[arutha]

Bernie,
will let you know how they turn out, I dont think you would want to use them on soft pivots

Jan,
I have sent you my address

Paul

[chris mabbott]

Paul, it would be a great help to me, and some of the newer guys if you could possibly snap a few shots of the setup and procedure of doing the repivot on the frenchie

[arutha]

No problem, will do

[bernie weishapl]

Nope Paul wouldn’t use them on soft pivots but would be nice to have one if it will hold up for those once in a while jobs.

[gerene]

Thought I give a little update on this clock.
Paul was so kind to repivot the fly arbor but unfortunately it has been in the mail on its way back to me for about 3 weeks now 😥 . I am starting to believe it is definitely lost.
So a new arbor will have to be made. The dimensions of which I can find on the movement except for the pinion. So I did a little study on gears to try to figure out what the dimensions of the pinion would be and more importantly what module cutter one would need to do the job. Therefore I counted the theet and measured the outer diameter of the previous wheel which I will call S5 further on and measured center distance between S5 and the fly.
N5 = theet count of S5 = 70
OD5 = outer diameter of S5 = 17.45mm
CD = center distance between fly and S5 = 9.2mm
According to J. Malcom Wild in his book “Wheel and Pinion Cutting in Horology” we can calculate the pitch diameter of S5 with the formula: PD5 = (OD5xN5)/(N5+2.76)= 16.79mm
To calculate the pitch diameter of the pinion on the fly arbor (PDF) I used the formula : CD = (PD5 + PDF)/2 or PDF = 2CD – PD5 = 1.61
I know the leaf count of the pinion is 7 so the module of the fly arbor pinion MF can be calculated by PDF/7 = 0.23 which would give the nearest cutter from Thornthon either 0.2 or 0.25
If I add the addendum of these cutters (0.17 or 0.21 for a 7 leaf pinion) to PDF, I get an outer diameter for the fly arbor pinion (ODF) of 1.61+2 x 0.17=1.95mm or 1.61+2*0.21=2.02 mm
Now my question is first of all are these calculations correct and if they are, do I take a module 0.2 or 0.25 pinion cutter. Not that I am starting to set up a pinion cutting facility immedately but I would like to know if I am correct about this just in case.

Jan

[gerene]

Did some further thinking about my calculations.
The module of the wheel and pinion should be the same.
So I calculated the module of the wheel with the formule (found in the above mentioned book)
M=OD/(N+2.76)
which gives us M5=0.24 which is close to the calculated module for the pinion (0.23).

Hope I am not boring everyone with too much math

Jan

[willofiam]

Hey Jan, currently I am figuring out these formulas, I will probably just be able to go thru your math (not much help I guess) But it will be a good exercise for me…… Are you going to buy a cutter or make one? My biggest issue in making a cutter would be once figuring out the module, how do I transfer that info to the cutter I want to make? Right now its all a bit confusing to me so thank you for the post about this, it is motivating me to get at it. William

[gerene]

Thanks William for taking some interrest in this. I know math can be hard sometimes . I appreciate that you try to go through my formulas, actually Malcom Wild’s formulas. I studied them too and think that I understand them now. That’s why I posted my calculations here, hoping someone would know something about them and warn me about eventual mistakes.
At the moment I am not considering buying or making a cutter yet, just trying to figure out how one should go in this situation. I think that I would buy a cutter from Thornton if I would go the make a new arbor myself route. For the moment I am just approaching it from a theoretical point of view.
Please let me know if you would have some doubts or problems with the formulas so we can try to fully understand them.

Jan

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