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Help Determining the Minimum Thickness of a Vacuum Chamber Lid

  1. May 28, 2018 #1
    Hello. I am attempting to build a large vacuum chamber for woodworking (used to infuse wood with resin/stabilizer). I would like to use a cast iron bathtub, similar to the one pictured as the vessel. I would ideally like to use a clear acrylic lid (with a rubber gasket) like the one on my little vacuum chamber I've been using. Can someone tell me if this is possible and if so how thick would I need it to be? would 1"-2" work? bathtub dimensions are 60"x30" THANKS!

  2. jcsd
  3. May 29, 2018 #2


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    Welcome to PF.

    Resin will condense on the clear lid. Flat surfaces will collapse under a vacuum. For vacuum treatment it is better to use a circular steel tube that you can slide your timber into on a small trolley. The tube would be open at one end where the door can be curved and will be much smaller than the length of the bath. If you must use a bath you should use a second bath, inverted as the cover.

    By allowing the tube to tilt slightly, and by providing a top outlet for the vacuum pump, with a low drain at the bottom rear, you can allow the treatment fluid to flow into the vacuum as required, and the excess to be removed later when the vacuum is removed.

    Building two identical systems next to each other makes it possible to cycle the loading, treatment and unloading cycles with the same fluid being transferred from one side to the other.
  4. May 29, 2018 #3
    The force from atmospheric pressure is roughly 65N for square inch (10N for square cm). 60*30*65N=117000N. That'll be equivalent with the weight of 12000kg, more or less, if I did the math correctly.

    I too think you should go with a tube instead.
  5. May 29, 2018 #4


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    I agree the absolutely best approach is to use a tube/pipe; fyi, by going to pg 505 of the below online copy of "Roark's Formulas for Stress and Strain you will find the method of calculating the max stress and center deflection for a rectangular plate, simply supported, under a uniform (pressure) load, where q = load per unit area ie psi.

  6. Jun 1, 2018 #5
    I suggest doing a search on vacuum bagging. You might just accomplish this with a thin membrane over the surface of your wood. Over a bathtub like this, I doubt that you will find a piece of plastic thick enough at a reasonable price. You might also investigate using this - https://www.smooth-on.com/product-line/ez-brush/ I don't know whether this technique will work for you, but it might be worth investigating.
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