Assist with correctly measuring and pocket watch crystal

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blubarb
Posts: 4
Joined: Sat Oct 15, 2016 11:44 pm

Assist with correctly measuring and pocket watch crystal

#1 Post by blubarb » Sat Oct 15, 2016 11:58 pm

Hi.This is my first post and apologies if the question has a self explanatory answer.

What I would like to know is what is the correct Ligne measurement for this pocket watch glass? (I am assuming they are measured in Lignes).  While looking on eBay I have noticed other figures included in the measurements and I am not sure what they refer to, eg: 25 Ligne size 25 4/16 is this 4/16 the height of the centre of the dome?

Thanks in advance. :)

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veritas123
Posts: 154
Joined: Sat Feb 11, 2012 2:53 pm

Re: Assist with correctly measuring and pocket watch crystal

#2 Post by veritas123 » Sun Oct 16, 2016 1:54 pm

Properly sizing Pocket Watch crystals can be a bit of a challenge over the internet. It's hard enough to do if you have the watch in your hand but getting a perfect fit by mail is tough.

A perfect fit on a PW crystal is were the crystal just "snaps" into the bezel. Kind of " Goldielocks " Not too tight, not too loose, Just right. That's because there is an undercut in the bezel that you can't accurately measure and must be taken into consideration for that " snap " fit. Also , as shown in your photos, an accurate measurement must be taken first , to establish a starting point . I can ashore you that your bezel does not have two different measurements from top to bottom and side to side. That is if it is undamaged, and your appears not to be.

As for the conversion from Linges to MM this chart will help most people , but yours is off the chart. In your case just order by MM.
crysize.jpg
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Don't forget to add the little bit for the under cut.

Here is another chart for the oversized crystals offered by a supplier on Ebay
crystal size large.png
crystal size large.png (15.78 KiB) Viewed 508 times
Next you must have hand clearance. That is called " dome " . Since yours is an open face it will be much easier. It is almost impossible to do remotely for a Hunter ( closed cover ) watch as too much dome and you can not close the cover.

Use this chart for " dome "
PwWatchGlassInfo3.jpg
PwWatchGlassInfo3.jpg (381.08 KiB) Viewed 508 times
The higher the dome number , the flatter the crystal.

The last decision is thickness and that is based on the style of your watch.

I hope this helps you, even if yours is not on the chart, to understand the numbers on the crystals.
Later production crystals will also state the size in mm with an assumed decimal point . Such as a 507 number on a crystal means it is 50.7mm in diameter

That same seller on Ebay currently has this crystal at 25 2/16 Lignes that he says measures 56.68mm with a dome.
56.68mm.jpg
56.68mm.jpg (33.15 KiB) Viewed 508 times
The long and the short of all this is , contact the suppliers with these large 23 - 25 ligne crystals and give them your dimensions , they will work with you to find the right one for your watch. You may have to buy a " range " to get a fit.

stryfox
Posts: 1951
Joined: Tue Oct 21, 2014 4:40 pm

Re: Assist with correctly measuring and pocket watch crystal

#3 Post by stryfox » Sun Oct 16, 2016 2:32 pm

This is great information.
Thanks for taking the time to share.

blubarb
Posts: 4
Joined: Sat Oct 15, 2016 11:44 pm

Re: Assist with correctly measuring and pocket watch crystal

#4 Post by blubarb » Sun Oct 16, 2016 8:49 pm

Some great information coming through. Thanks. Yes, I thought it odd that there would be two different measurements, perhaps I dan't apply enough pressure on the Vernier - I will do it again. Anyway, great stuff.

WCMFG
Posts: 6
Joined: Wed Jul 20, 2016 10:23 pm

Re: Assist with correctly measuring and pocket watch crystal

#5 Post by WCMFG » Sun Oct 23, 2016 6:12 pm

blubarb,

If you are unable to secure a crystal for your watch, I would be happy to supply a new one at reasonable cost. I currently make almost any style of round glass pocket watch crystal. Please feel free to contact me if needed.

William White
White's Crystal MFG
PO Box 460532
San Francisco, CA 94146
http://www.whitescrystals.com

blubarb
Posts: 4
Joined: Sat Oct 15, 2016 11:44 pm

Re: Assist with correctly measuring and pocket watch crystal

#6 Post by blubarb » Sun Oct 23, 2016 7:57 pm

WCMFG wrote:blubarb,

If you are unable to secure a crystal for your watch, I would be happy to supply a new one at reasonable cost. I currently make almost any style of round glass pocket watch crystal. Please feel free to contact me if needed.

William White
White's Crystal MFG
PO Box 460532
San Francisco, CA 94146
http://www.whitescrystals.com
Thanks, William. I have one on the way but whether it fits or not will be the thing. I will certainly contact you if need be and great to know that you offer this service!

John

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