Dropped my tank off at the machine shop. I'm having them thread holes for 8 bolts and slice a ring off the top to sandwich the acrylic with. We'll see the results soon. Thanks for everyone's help.
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Acrylic Thickness
- Thread starter 350xfire
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DIWdiver
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mts0628
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Hey Hector:
Did you already get your acrylic disc? I thought about suggesting this, but I knew your lathe wasn't coming until the 25th. Anyway, I was going to suggest cutting the disc a bit bigger, say to 8 inches. This is a larger diameter than the AL80, but think it would be nice to have a bit more material behind the areas drilled for the studs. This would be a consideration for a higher pressure pot. Sorry so late. :depressed:
Have a good night,
Thomas
Did you already get your acrylic disc? I thought about suggesting this, but I knew your lathe wasn't coming until the 25th. Anyway, I was going to suggest cutting the disc a bit bigger, say to 8 inches. This is a larger diameter than the AL80, but think it would be nice to have a bit more material behind the areas drilled for the studs. This would be a consideration for a higher pressure pot. Sorry so late. :depressed:
Have a good night,
Thomas
You want to use an O-ring. Flat gaskets require tooled seerated rings in the set to be remotely effective over about 50 psi.
Has anyone tried Lexan instead of arcrylic? It is a lot stronger. That is what we use for the face plates of our diving helmets so they don't end up like this:
before you assemble your unit you can reduce the chance of craking of the plate by rounding ALL sharp corners with a small file. Sharp changes in the material cause increases in the internal stress of the material under load.
I also reccomend that you hog the O-ring groove out with a round bit to seat the O-ring too. Should be half as deep as the O-ring is thick in diameter.
Has anyone tried Lexan instead of arcrylic? It is a lot stronger. That is what we use for the face plates of our diving helmets so they don't end up like this:
before you assemble your unit you can reduce the chance of craking of the plate by rounding ALL sharp corners with a small file. Sharp changes in the material cause increases in the internal stress of the material under load.
I also reccomend that you hog the O-ring groove out with a round bit to seat the O-ring too. Should be half as deep as the O-ring is thick in diameter.
mts0628
Contributor
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You want to use an O-ring. Flat gaskets require tooled seerated rings in the set to be remotely effective over about 50 psi.
Has anyone tried Lexan instead of arcrylic? It is a lot stronger. That is what we use for the face plates of our diving helmets so they don't end up like this:
In the words of Adam Savage on Mythbusters, "Well there's your problem!" As far as Lexan, it is better but I have not been able to source it economically [yet].
And 350xfire, I'd go with muddiver and say o-ring. Flat gaskets are finicky but then again, it depends on what you're using material-wise.
Looking at AOPTec, there are:
........................Nominal.............................Actual
Dash#.........ID.............OD...........CS......ID.............OD
2-440........6-3/4.........7-1/4........1/4....6.725........0.275
2-441....... 7...............7-1/2........1/4....6.975........0.275
2-442....... 7-1/4.........7-3/4........ 1/4....7.225........0.275
I dunno how thick an AL80 is, so you might be better off getting a couple of different sizes of o-rings and play around with them. They're cheap, good quality, and the minimum order is 5 USD anyway.
Good luck!
Thomas
DIWdiver
Contributor
Wall thickness -
The wall thickness of the '80 that I opened for my pressure pot is about 0.53". I was very surprised to learn that the tank was not really very round. To get the ID and OD both round, I ended up with a wall thickness about 0.48".
O-ring vs. flat -
I will second Thomas' recommendation for an o-ring instead of a flat gasket. They are (surprisingly?) way more forgiving of slight imperfections on the surface and in the installation. A 1/8" cross section o-ring should be compressed about 0.030". This allows it to follow surface imperfections such as bowing and tool marks. How much force (bolt tension) does it take to compress a flat gasket even 0.005"?
However....
If you've already sent the tank to the machine shop, then they already know what to do or not do for the o-ring. If you haven't got a properly designed gland (space for the o-ring), then it may be very hard to get a proper seal. What does the book suggest for a seal? If you're following his mechanical design, you should follow his seal design as well. It's proven.
o-ring groove shape -
I have what I consider the o-ring bible, the 146-page 'Seal Design Guide' from Apple Rubber (Apple Rubber Products Medical Seals, AS-568A/AS-568B Standard and Custom O-Rings, silicone housing seals, face seals, injection molded part, and medical grade silicone seals) and it recommends rectangular "glands" for o-rings. A half-round gland would not allow for the ring to deform into the open space of the gland as it gets compressed. The volume of rubber doesn't change, only the shape does. That material has to have somewhere to go. Plus, round tools are much harder to make than rectangular.
o-rings general -
Apple Rubber have a lot of stuff online too, but I didn't bother to register to get at the best stuff, since I already have the book. I recommend that anyone who wants to design with o-rings either get the book or register and read on their web site. Their book has been invaluable to me.
D
The wall thickness of the '80 that I opened for my pressure pot is about 0.53". I was very surprised to learn that the tank was not really very round. To get the ID and OD both round, I ended up with a wall thickness about 0.48".
O-ring vs. flat -
I will second Thomas' recommendation for an o-ring instead of a flat gasket. They are (surprisingly?) way more forgiving of slight imperfections on the surface and in the installation. A 1/8" cross section o-ring should be compressed about 0.030". This allows it to follow surface imperfections such as bowing and tool marks. How much force (bolt tension) does it take to compress a flat gasket even 0.005"?
However....
If you've already sent the tank to the machine shop, then they already know what to do or not do for the o-ring. If you haven't got a properly designed gland (space for the o-ring), then it may be very hard to get a proper seal. What does the book suggest for a seal? If you're following his mechanical design, you should follow his seal design as well. It's proven.
o-ring groove shape -
I have what I consider the o-ring bible, the 146-page 'Seal Design Guide' from Apple Rubber (Apple Rubber Products Medical Seals, AS-568A/AS-568B Standard and Custom O-Rings, silicone housing seals, face seals, injection molded part, and medical grade silicone seals) and it recommends rectangular "glands" for o-rings. A half-round gland would not allow for the ring to deform into the open space of the gland as it gets compressed. The volume of rubber doesn't change, only the shape does. That material has to have somewhere to go. Plus, round tools are much harder to make than rectangular.
o-rings general -
Apple Rubber have a lot of stuff online too, but I didn't bother to register to get at the best stuff, since I already have the book. I recommend that anyone who wants to design with o-rings either get the book or register and read on their web site. Their book has been invaluable to me.
D
I originally thought about using a flat gasket and told the machine shop to machine a groove leaving 1/8" on each side and 1/16th inch deep to prevent the gasket from slipping. In my opinion a flat gasket provides more surace area to seal. I can get custom gaskets cut at Stuart Hose in Levisville, TX. I can however use an o-ring as well and they would be able to get it. Just have to figure out the diameter. I think it would be about 7-7 1/4".
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