Vacuum Chamber Lid Fail

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vtgaryw

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Heard a noise out in the garage, and this is what I found...

That's 1/2" Plexi. I've used this lid numerous times. Had two drilled and tapped holes in it, one for the vacuum with a shutoff and one for a gauge (which I had borrowed for something else, so that threaded standoff was just capped off.) No cracks, because before using it today I had just wiped it down to clean it.

Used this dozens of times, I would have thought 1/2" plexi was enough. Looks like I'll have to rig up the pressure pot to do vacuum now, but I really liked the clear lid.

-gary
 

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frank123

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Try using Lexan (Polycarbonate).

It's far tougher and more durable than Plexiglas (Acrylic).

It's used for bulletproof shields and aircraft windshields.
 

vtgaryw

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Didn't wipe it down, I learned that years ago in shop class in 8th day, we actually got to work with the stuff. I did, however, spill some vacuum pump oil on it. I wonder?

I just looked up the physical properties of polycarbonate verses acrylic - interestingly enough, while the impact strength of Lexan is far better than acrylic, acrylic is around 25% higher in both tensile strength and flexural strength.

Gary
 

frank123

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Didn't wipe it down, I learned that years ago in shop class in 8th day, we actually got to work with the stuff. I did, however, spill some vacuum pump oil on it. I wonder?

I just looked up the physical properties of polycarbonate verses acrylic - interestingly enough, while the impact strength of Lexan is far better than acrylic, acrylic is around 25% higher in both tensile strength and flexural strength.

Gary


You can bend a window pane sized sheet of polycarbonate into a "U" shape without breaking it, you can't do that with acrylic.

People living on golf courses often have lexan protection sheets put in front of golf ball susceptible windows and golf balls leave a distinctive dotted pattern on the lexan when they strike it but don't break or crack it, acrylic will develop cracks and break the same as glass will even if it needs a harder ball strike than with glass to break it.

The advantage of Acrylic is that it is much harder and will remain perfectly clear with normal (gentle) cleaning while Lexan will develop very fine scratching from dust or hard fibers of paper towels and requires much more care to avoid degrading its clarity.
 

robutacion

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Clear acrylic is the cheaper option but the 1/2" is just not enough. I put a 1" lid on mine, I could get away with the 3/4" the only problem is that after many times cleaning it from the CJ, the inside surface becomes less clear, the CJ does attack the acrylic pretty bad.

My next lid will the tempered glass, it will stay clear forever...!

Cheers
George
 

vtgaryw

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I'm sure it was weakened by drilling into as well.

Has anyone made a Lexan Cover for a HF Pressure Pot? Did a quick search but didn't see anything come up. You'd have to figure out how to gasket it. If I still had access to a CNC, I could mill a groove in the Lexan, but, alas, I don't.

Gary
 

frank123

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I'm sure it was weakened by drilling into as well.

Has anyone made a Lexan Cover for a HF Pressure Pot? Did a quick search but didn't see anything come up. You'd have to figure out how to gasket it. If I still had access to a CNC, I could mill a groove in the Lexan, but, alas, I don't.

Gary


For vacuum, a simple flat soft rubber gasket will work fine, the vacuum sucks everything together and seals it. If necessary, which it shouldn't be as long as the mating surfaces are smooth, a light coat of silicon grease or even vegetable oil on the gasket should make the seal perfect. Rubber gasket sheeting is usually available at places like ACE hardware.

Pressure would be a different situation than vacuum.
 
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