With a good quality venturi the best I could pull was around 25-26 on a good day. With the rotary vane pump I could pull a fraction over 29 from memory.
Where did you find that V-2 vacuum pump - - - - that's a size I'm looking for!Update
I have determined that my old vacuum pump has about 1.5 CFM of flow and I think twice that is needed. The vacuum chamber I ordered finally arrived but the way they mounted the manifold to the pot is crappy. It allows the manifold to wiggle around and it does not seal. So before I can move on I need to get another pump and fix the vacuum chamber. I have an old portable compressor that has a pump that looks just like my vacuum pump but is twice the size. Something is wrong with it as at about 60 PSI the motor bogs way down. If I can get it to run properly I will replumb it to be a vacuum pump. I also have a V-2 compressor pump with a 3 HP motor. Way bigger that I want or probably need.
That's very VERY niceUpdate:
Good Bad and Ugly
I have been keeping busy working out what size element works best in my homemade kiln. And getting a proper size vacuum pump and vacuum chamber setup. During this time the patterns I had printed with castable resin sat on a shelf and warped. So lesson learned, print and cast right away. I used the patterns anyway.
My second attempt was not as good as my first. Two problems, first my plaster was probably to soupy. And that caused problems that resulted in cracks forming in the plaster during burnout. The cracks fill with metal and leave flashing on the parts. I had lowered the first stage of the burnout from 300 degrees F to 230 degrees F and should have lengthened the hold time by and hour. The second problem was pouring my brass at too low a temperature. I could tell I had a problem as soon as I poured. You can see the difference in the surfaces of the spurs. Could also be problems with the flask temperature. My first go the flask was cooler by 100 degrees.
I need to keep better records of what I have done, what worked and what did not.
Still there was a bright spot. The little wheel turned out OK and demonstrated how thin a part can be and still cast completely. The spokes are .060” wide and .040” thick. The little speed handle cast OK as well but I bent it cleaning the plaster off ( and then broke it off). This part needs to be cast in Bronze, the pokes are to soft and bend easily. After a light sand blasting it looked like a usable part.
Burnout was complete and that is good to see. Perhaps I can shorten the final high temp hold time a bit. And I had far fewer and smaller little metal balls on the parts. Most all of them would pop off with a little pressure with a pocket knife. I was much better organized this time and I think my problems are entirely operator error.
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