Advice needed on Choosing Crystal Type

[Hoe]

Dear all

I need some advice on choosing the correct crystal parts (crystal size, gasket) for a yet unfinished, unbranded watch project I recently bought.

Looking at the case construction, I can’t figure out, what kind of gasket or crystal will fit. An undercut makes my decision difficult. I attached a sketch of the contour of the watch’s case with measurements.

What would you do?

Best wishes

[jdm]

3 hours ago, Hoe said:

Looking at the case construction, I can’t figure out, what kind of gasket or crystal will fit. An undercut makes my decision difficult. I attached a sketch of the contour of the watch’s case with measurements.

I believe the case is made for a regular I gasket, to be fitted cautiously. Then you can use any standard crystal you like. https://www.cousinsuk.com/product/iring-height-120mm-sternkreuz

[rodabod]

That’s quite a large rebate/groove around the perimeter - 0.5mm deeper than the actual edge of the crystal. 
 

What age is the case? Was it made by Monnin? 

[Hoe]

Thank you for the answers so far.

I can only imagine a CousinsUK gasket 35.3x34.5 with height 1.75 together with a crystal MFH 34.5. But will this choice lead to a secure fit? Looking at the section cut I assume, there must be some other type of crystal gasket. One that fits into “D 36 mm”.

Besides “Swiss Made”, “Stainless Steel”, and “Waterproof”, there is only the number “3174.20” engraved in the case back. I don’t know the age or the manufacturer of the case. I found a photo of a watch with a similar appearance.

 

[jdm]

3 hours ago, Hoe said:

Thank you for the answers so far.

I can only imagine a CousinsUK gasket 35.3x34.5 with height 1.75 

Should be 1.20 or 1.25mm high to fit in the groove, but if  the OD is then smaller than the about 36 you drawn it would not hold well laterally. Unless you want to try to print you own reverse L shaped gasket (which seems excessive), perhaps the safest approach is to open the top on the late to an uniform diamenter, and fit a 2mm thick crystal. Or fill the grove and fit a 35mm, 1.75mm high gasket.

[rodabod]

That looks like the Porsche Design case. Possibly made by Monnin judging by the case back. 
 

Are you sure the widest section is really ~ 36mm?

 

[Hoe]

I am not 100% sure about these 36 mm, it’s a guess. I don’t have the measurement tool to reach into the groove.

I am thinking about filling the groove with an I gasket and add another one to hold the crystal.

[jdm]

42 minutes ago, Hoe said:

I don’t have the measurement tool to reach into the groove. 

Cut a thin, long piece of packaging plastic with rounded tips until it fits precisely in the groove, then measure it with calipers. 

 

42 minutes ago, Hoe said:

I am thinking about filling the groove with an I gasket and add another one to hold the crystal.

That will  as long at least the inner diameter  of the larger gasket is flush with the top case opening. Otherwise the smaller gasket won't rest on it and is a wasted effort.