Techniques for measuring glass size.

[Paul78]

One of the things we do a lot of in the shop is put in new watch glasses, in fact its probably our second most popular service after battery replacement. Sometimes when the glass is completely broken and the only way to measure it is by measuring the inside diameter of the case it can be a bit tricky when there is also a gasket. I tend to get it right most of the time, and can generally just try a few different sizes if i have them in the stock. But occasionally it may be a large glass, a 374 for example, and i don't have it in stock as my bulk stock only goes up to 350, so i measure the diameter and the digital verneir says 374, so thats what i order. When the glass comes i try and fit it and its too small, by a whisker! sometimes if i promise the customer it will be ready for tomorrow say, i will order a 373, 374 and 375 - surely one of them will be right, but this obviously lowers profit and i'm sure to use the others at some point.

So my question is, whats your method of measuring, and is it usually right?

 

[Ishima]

No special techniques however If I get a measurement such as 374, I'll be thinking it's probably 375. Most glasses are in increments of .5 in my experience. 

I also build up a stock of previously used sizes, so if i know that it's a 375 i'll order 2, useful to know I'll have the glasses for any customers returning for the same glass,  or that for popular watches I commonly finding myself doing glass replacements on, I know I'm stocked for (helps keep the workload clear if you can do a job as soon as you find yourself with the time) and also in the rare event a glass gets scratched or damaged during fitting, you have a back up. 

I'm not sure about the whole profit margin thing. I charge enough for glass replacements that ordering an extra glass or two hardly seems worth splitting hairs over. And as you say, they'll get used so it's an investment, not just a simple loss of revenue. 

Edited December 19, 2016 by Ishima

[vinn3]

very good advice !  order 3.   IT;S ONLY MONEY  also  is that 1  or 0.5  mm ?

[BobHadababyitsaboy]

With a reliable pair of calipers, it's generally pretty easy to measure the exact size of a crystal you can remove intact. If you have to break the crystal and measure the inside of the bezel, I would generally measure and order -.1mm, size measured, and +.1mm. Crystals (especially simple flat ones) are pretty cheap and the shop I work at will usually charge around $30, so there's still plenty of money to be made. And, like Ishima said, those extra crystals are always great to have in stock, as they will come in handy. 

[ramrod]

i've usually measured the glass with a caliper and then convert the size to MM. but, i'm finding that this takes the guesswork out of the equation: i look up the case (usually a seiko) on the borel's website and see what the stock glass was. if it says 300T12ANS, i know it's a 30mm. no guesswork involved.