Making the Vacuum Chamber

Now that I can generate vacuum, I need a place to generate vacuum in and that’s a vacuum chamber.

Commercial/scientific vacuum chambers are expensive…like sometimes into the thousands of dollars expensive. Though one would be nice to have, I have neither the money nor the necessity for that level of chamber. What I need is something vacuum tight that can hold that vacuum long enough to provide utility.

I’ll be using an 8 1/2″ diameter Pyrex bowl, an acrylic chopping board, and some other bits to hang it all together. The bowl will need to seal against the acrylic board and to do that it will need a gasket. I have an old backpacker’s sleeping pad that I use whenever I need closed-cell foam and that’s what will make my gasket. The bowl itself has a 3/8″ lip around the edge which will make attaching the gasket easier.

I used Contact Cement on the lip, turned the bowl over and placed it on the foam, then I added a few pounds of weight to the bowl to ensure a good seal and bond:

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I let it set up overnight, then cut the foam away, leaving a gasket around the edge of the bowl:

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Because each component of this chamber could leak, I decided to test each component as I added it for vacuum tightness to make fixing what leaked easier. As with the V1.0 version of the pump, there was a V1.0 version of the chamber (which didn’t work; don’t use plywood for the base). I’d already checked the gauge and release valve for tightness, so each time I drilled a hole and screw a fitting in, I tested it:

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Yes, the acrylic board is a bit thin and under the pressure it bent. I’ll fix this later by adding stiffening legs underneath it to minimize the deflection.

It’s really a simple thing to build and it didn’t take long. This is the (mostly) completed vacuum chamber (because there are always tweaks, y’know). As you can see, I used some scrap wood to make the stiffening legs and they work fairly well. There is still deformation but it’s well within tolerances:

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I attached the release valve using cable ties:

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Because the surface of the acrylic board has a pebbled texture, I was curious to see if the foam gasket would seal well enough and it does. However, in using the chamber, I found a couple of problems to address.

During the construction of the pump, I wasn’t entirely sure that the 3″ section of pipe that connected the flange to the reducer had bonded properly and it turned on it hadn’t. Though the 3″ section bonded very well to the flange, only half of it bonded to the reducer and that snapped free. It doesn’t affect the pump’s ability to create suction, but it does compromise its strength. So I used screws to attach the loose section of pipe to the reducer:

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I’ve used the pump a number of times since its construction (and fix) and it’s holding up well.

Another thing I noticed during its first use is that the vacuum bleeds off over time. It takes just under two minutes to go from about 27″ of vacuum to 0″. In using it, I discovered that 15″ of vacuum is about the minimum I want to work with and that equates to a lot of pumping! I diddled about a bit. I added cable ties to seal the hose to the fittings more tightly and that decreased the vacuum bleed off a little. I still don’t know why I did this, but at one point I held the piston up (because vacuum with this pump is created on the up-stroke; it looks like a plastic bicycle pump but operates in the reverse in all ways). I noticed that this slowed the vacuum bleed off substantially. So I drilled a hole across the body of the piston and use a coat hangar to hold the pump up:

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And that is the vacuum chamber. It works well enough for my purposes and has enabled me to create nice molds and castings. I’m pleased with my efforts and very pleased to have the added capability to copy parts!

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