But, and I accept suggestions here, it will not pull a vacuum. The vacuum pump, which is one of the old Clisbys, is working fine. If I put my finger over the hole it goes straight to 28+ inches of Hg. But with the NEW gasket in place, and just about every old and new gasket I could find or make from the stuff I have around, except the old one which I stupidly threw away, it will not go above 5 inches Hg.
Since the middle gaskets were of electrical tape, and since clay got real dry around the gaskets if the mill was not used for some time, I made new ones out of Buna-N rubber, the same rubber that separates the top and bottom pieces on my Shimpo stainless steel mill. I also made the vacuum chamber gasket out of this Buna-N rubber but it really leaks. Badly.
I have a really nice lap wheel and so took one of the metallic diamond pads and attached it to a flat piece of metal, and sanded the top of the vacuum chamber until it was flat, which took some time. Did not help a lot.
The top piece of plexiglas is the piece that came with the pugmill and it is not totally flat and many years old -- close to 25 probably. I tried some other pieces of thin plexi and they did not work either.
So. What to do? The first thing is that I will block off the vacuum chamber leading into the pugmill and make sure it's the gasket at the top of the chamber that is the problem. I think it is but it could be the Buna-N rubber which runs down the seam of the top and bottom pieces of the chamber, or the Buna-N pieces that protect the plates where the screens are extracted. I don't think it's this because the Shimpo works fine with the Buna-N.
I do not tend to have great mechanical ability. A problem like this one stumps me for some time. The mill has lots of clay in it so it's not open at the end, as a Venco can tend to be. Interesting problem.