The vacuum chamber on eBay sold for $491, not much over my max bid of $407, which is an excellent price considering buying it brand new would have cost at least $3KUS not including the $500US pump nor the $150US chrome wire cart. Too bad the chamber was too small.
I spent the weekend designing a larger vacuum chamber (Many thanks to Abbess!) and here is what I came up with:
The one on the left is the 30″ O.D. (27″ I.D.) chamber and the one on the right is the 24″ O.D. (21″ I.D.) chamber. Each chamber holds a mock-up of the copper cavity and includes a 3″ square section at the cavity’s narrow end we will need for tuning. Unfortunately, the 24″ chamber is too small as the tuning part at the end of chamber gets cut off and it still doesn’t include enough space for a scale.
I could rotate the chamber and cavity so it sits upright:
The pipe is made out of HDPE (High Density Polyethylene) which, depending on wall thickness, can handle up to 267psi. The door is a 2″ thick clear cast-acrylic sheet which should be sufficiently thick because Abbess uses a similar width for a 36″ wide chamber:
The back and front supports shown in green are 2″ thick HDPE plate and the front support has an O-ring embedded in it (shown overly large) and will be clamped like the picture above.
The walls of the pipe are about 1.5″ thick which conforms to a common “DR 17″ type of HDPE pipe which can handle 100psi, well in excess of the 15psi necessary for a vacuum under full atmospheric pressure at sea level. The chambers are three feet long which, for just the pipe, would make the 30″ O.D. weigh (68lbs/ft) 204lbs and the 24″ O.D. weigh (43lbs/ft) 129lbs. This doesn’t include the pump (35lbs), the two plates of HDPE nor the acrylic door, which will likely put the 30” chamber over 300lbs.
The costs are still being figured out, but they will be roughly:
- 30″ diameter, 1.7″ wall thickness, HDPE pipe – $500
- 24″ diameter with a thicker wall (DR 11), quoted at $390CND for 3ft
- 30″ square 2″ thick HDPE plate (x2) – $300 each – $600 (hopefully cut)
- 24″ square, 2″ thick quoted at $200CND
- 2″ thick clear cell-cast acrylic – $600 to $800
- 24″ square 2″ thick piece, quote at $300CND
- 29″ diameter O-ring – $40 – The “Viton” o-rings are apparently the best for Vacuum chambers and I am probably going to need three of these, one between the back support and the pipe, the front support and the pipe and the front support and the door.
- A 23 1/2″ diameter, 1/4 diameter o-ring Viton, quoted at $25CND
- Hinges and fasteners – $50
- 30″ wide cart that can handle 400lbs (these are actually quite common with chrome wire carts that can handle 800lbs) – $300
- 3/8″ threaded pipe to hook up to the pump – $15.
- Port and N-type parts to get the microwave signal into the cavity – ???
- (PURCHASED) 7CFM Vacuum pump – $400
Total for 30″ (not including the pump): $2300CND (based on estimates)
For 24″ (not including the pump): $1530CND (based on quotes)
This doesn’t include fabrication costs, most of which I will do myself, although getting the HDPE heat welded will probably add more. I have also been thinking I can bolt everything together with O-rings, but I want to talk to the plastics supplier first.