This is how I made my Vacuum pump. I wanted to use a vacuum degassing unit as described in the book "Plastic Resin Bonded High Energy Rocket Fuel Systems" volume III by Gary Purrington 1989. I also wanted to do this cheap. Using a picture and description I found on the web and with permission to use it, I built this vacuum degassing setup. I bought some Lexan and Home Depot to use as the cover over my Kitchenaid mixing bowl. I put the bowl upside down on the Lexan to trace the outer edge. I made the circle to be a little bit bigger that the bowl. So I used a 1/2 inch washer. I put the outside of the washer against the outside of the bowl and then put the pen on the inside of the washer to trace around the outside of the bowl. Then using a saber saw I cut the out the Lexan. Because I have my center ring jig made up. I used it to cut the outer circle so it was nice and clean with a perfect cut. Then I measured the inner and outer diameter of the bowl to cut a small groove in the Lexan to fit the bowl rim. Again using my center ring jig and lowering the bit so it would cut into the Lexan only by 1/16 of an inch, I cut the groove. Next I test fit the bowl and it worked. Now for the seal I filled the groove with rubber silicon and let it dry. Using some old brass parts I had laying around, I installed a relief valve after drilling a hole off to the side of the middle. Next I installed the brass port to hook up to the vacuum pump. I tested it using my A/C manifold gauges and vacuum pump. It sucked down to 23 inches. That's all we get in Denver due to the altitude. Should work great. I got the vacuum pump from the refrigerator used as the curing box. Even though I had a pneumatic vacuum pump, my air compressor would have to run a lot to keep a constant vacuum. Since I had the one from the refrigerator pump, I decided to use it instead. It doesn't create a vacuum as fast so it more controllable. It took a few times of cycling on and off to where it would stay on. It only does this when it’s cold out like in my garage. Once it starts working, it's great. So now all you have to do is place the top over the mixed propellant in the bowl and start the pump. You have to press on the cover to help seal the unit until there is enough vacuum to hold the cover on. Once that is done you have to watch the propellant to make sure that it does not get sucked out of the bowl into the vacuum tubes. This can been controlled by slightly opening the vent valve to keep a constant vacuum on the mix without having it go all over the place.
Pictures of the Vacuum Degasser