Demystify PW Crystal sizes … Please

[cusimano]

Hello All,
I have a beautiful Waltham PW that needs a crystal.
The mystery is witch crystal to purchase based on what is marked on the NOS crystal ….
Example: the crystal opening on my open face PW is 47.5mm which translates to 21 1/16 lignes ….. I get that.

What I don’t get is what is the stickers on the crystals …
most have 3 numbers and for the life of me I can’t make sense of them ….
20 7/16 …. 23 2/4 …. 7
15 15/16 … 11 7/8 ….. 6

What gives ?
Please explain this mystery to me ….
Thank you for your insights ….. I’m sure I just need my eyes opened.
Chris

[stevefitzwater]

http://people.timezone.com/library/workbench/workbench631691117422306218

Here Is a read on the subject…

Did you find a barrel for that heirloom?

[cusimano]

Thanks Steve,
And Yes I did find a barrel ….. Thank you for asking

[stevefitzwater]

Not sure that link will demystify it, but it might help explain the different measurements…

If I have the old crystal I will measure that, if not, I measure the opening in mm, then I go to otto Frie or Esslingers and dig through their website to find the crystal style then size. most will have to measurement in mm.

I usually order the size I think it is and then next size bigger, these VTF crystals are brittle, more so then others I have worked with, do not force (and by force mean with any pressure, instead of pressure LIGHTLY warm the bezel to help it expand, I start out with simply placing the bezel in my pocket, if that does not work I will warm a piece of copper with the bezel on it over a flame, I touch the bezel frequently ensuring it does not get too hot, if I can not pick it up, it is too hot. Again DO NOT OVER HEAT IT, if you get it too hot you will not be able to pick it up and work on it and other bad things happen that would render the bezel to the junk pile…

I still find crystal fitting to be one black arts of Horology and only the highest Horologists can do it properly. Unless I am getting a Sapphire crystal, I get the size I think it is and one bigger, normally the bigger one is the perfect fit.. but not always. Heck I have even had to re-order the smaller size and use the UV cement as the only method to get a good fit.

[cusimano]

Thanks Steve

[tmac1956]

Chris:

This helped me a great deal….

http://www.daveswatchparts.com/PWCrystals.html

Later,
Tom

[stevefitzwater]

been doing some searching on Bezel Warmers, and well… it seems they can be easily made, first a metal tube, a light bulb, and a cap, some talk of simply placing a used, clean soup can over a light bulb and warming it that way.

To make your own should be a simple a quick task, either by the soup can method, or simply gathering the parts to make a more professional looking one, so the key that determines the other item sizes is the light bulb and it’s socket, so get a small surface you want to attach it to, board, metal, etc and mount the socket on it and screw in the light bulb (incandescent). Then measurer for the size of tube you want, the tube should be just wider and taller then the light bulb, but not touching it, so the heat from the light bulb transfers to the metal tube, once you have the diameter and length, you will need to find a top for the tube to serve as the work surface, I would go with brass or some soft metal, so it will not scuff the bezel accidentally..

For you guys with a lathe, I would simply turn a brass disc with a lip, then press fit the top into the tube and your done, I suppose you could get fancy and put a dimmer on the bulb to manage the temp..

Then simply turn on the bulb and allow it to warm the bezel, so who wants to start making these??

[tmac1956]

All:

I use my coffee pot warmer. It seems to work well.

Later,
Tom

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