Questions regarding crystal gasket sizing and compression

[SQ19HRLGY]

I've read on another thread to not account for compression when changing crystals + gaskets and to simply follow the rule of

Case Inner Diameter = Gasket Outer Diameter and Gasket Inner Diameter = Crystal Outer Diameter

However the measurements of the original factory parts on my watch suggested otherwise

Case ID is 30.5mm
Crystal OD was 29.5mm
Gasket ID is 29.5mm
OD of crystal + gasket is 30.6mm (so I've noticed that .1 mm can be compressed)

Now I found a gasket with a ID of 29.35 and OD of 30.5.

Will the .15 difference compress for a snug fit or does compression only work for differences on the outer diameter (will my crystal break)?

Also, will a gasket with a matching ID of 29.5 and OD of 30.5 work better?

Many thanks

[oldhippy]

I think you are being a little fussy, why because when it comes to gaskets you can buy assortments from suppliers, from that selection you can find one that fits. If the back doesn’t screw down properly you know you have the wrong size or shape. With crystals if it is  a high dome and you use one of these (see photo) you can squeeze it to fit, in other words if it is a size too big it will fit providing it doesn’t look stupid in height. Tension ring glasses are different if you do not have the right size they will not fit and you need the proper tool to enable them to fit correctly. The high grade watches you should be able to order the correct gasket and glass. When it comes to glasses there are to many types to mention.

 

[SQ19HRLGY]

So... can I use the 29.35 gasket without worrying about my crystal breaking? Or am i better off with the 29.5?

Apologies to you and other veterans if I come across as too fussy, but I'm a new hobbyist who is trying learn the general rule of thumb for sizing gaskets. I want to understand what I can get away with in terms of compression so I don't break expensive sapphire crystals on a regular basis. As mentioned before, even after reading multiple threads and sites, I am a bit confused.

I have done enough research to be well aware of the many crystals, tools, and assortments out there, and to know that with high grade watches it is much easier to order correct sizes. However that wasn't the question. This is not a high grade watch and the sizing is rather awkward. I've already found 2 gaskets that should work and I am simply asking which of the two will logically work better and if either will break my crystal.

Hoping you can shed some light for this newbie!

Many thanks again

 

 

[dadistic]

It might help if you tell us what watch you are working with, there are many different methods of fixing a crystal, I think @oldhippy may be thinking of the wrong type. 

So, if you trying to mount a sapphire crystal into an l-gasket on a Seiko watch, then you are best off using the original l-gasket if it is serviceable.  If not, then purchasing the OEM replacement is the way to go I think. The replacement crystal should be the exact same diameter as the original.

There are other people here with more experience with this type of crystal than me, hopefully they will chime in. Ultimately, it is  experience that will determine whether or not you will break crystals. I just cracked one yesterday, it was an acrylic that needed finishing to fit properly, and I got a bit too enthusiastic :-) I've been doing this for a while, too.

Good Luck

[oldhippy]

The smaller of the two gaskets should be fine. It is better to stretch it a little, then to have one bunched up when screwing the back on. Even if the back Is a press on a bigger gasket can become trapped.

[SQ19HRLGY]

On 5/21/2018 at 11:35 AM, dadistic said:

It might help if you tell us what watch you are working with, there are many different methods of fixing a crystal, I think @oldhippy may be thinking of the wrong type. 

So, if you trying to mount a sapphire crystal into an l-gasket on a Seiko watch, then you are best off using the original l-gasket if it is serviceable.  If not, then purchasing the OEM replacement is the way to go I think. The replacement crystal should be the exact same diameter as the original.

There are other people here with more experience with this type of crystal than me, hopefully they will chime in. Ultimately, it is  experience that will determine whether or not you will break crystals. I just cracked one yesterday, it was an acrylic that needed finishing to fit properly, and I got a bit too enthusiastic :-) I've been doing this for a while, too.

Good Luck

Ah I should've mentioned that its a wenger field watch that held a flat mineral crystal with straight sides. I did mention though that I just bought a domed sapphire of the same diameter to replace the flat mineral so I'm not sure why oldhippy keeps talking about casebacks.. 

All I wanted to know is how much do crystal gaskets compress, if at all? And do I need to account for this (contrary to what another thread quoting esslinger said)? I wanted to know before I spend money on gaskets and crack an expensive crystal, but as you mentioned it seems to be the consensus that only experience will determine this 

Related to sizing - the sidewalls of the seating for the crystal are 1.1mm high. Would I be able to use a gasket that is .9mm high as long as the width/diameters fit? Or are there problems that im not aware that i'll run into?

[oldhippy]

I did not know what type of case it was. I gave general advice on how a wrong type of gasket could affect the closing and sealing of a case back. I am sorry if I confused you in any way.