MAKING A VACUUM CHAMBER OK, so you want to make molds?  You want to de-air your SILICONE...well, here you go.  This is the simple, and not as expensive (if you have an air compressor)  method. The materials are the cheap part.  The air compressor won't be.   This method will be loud, but hey, you take the rough with the smooth. Shall we begin?  OK then, lets! A list of materials to find, and where I found them locally in Ohio, as well as the approximate prices: A venturi vacuum valve, sounds tough, but it isn't. At Harbor Freight Tools I found one for $10  If that link doesn't take you to the page, just run a search on their site for "AIR VACUUM PUMP" and it should come up.  I bought mine on sale, I think the normal price may be double that, you may have luck at other stores.  The "guts" are all you need, as shown in this picture, removing it is a matter or unscrewing the two fittings and 4 screws, I took the handle off to save, the case is going to be recycled. A vessel of some sort to contain everything. I bought this steel jar a year ago with the intentions of making a chamber then, but never found the parts until now, or had a need for that matter.  I picked this up at a discount store for $6.99 plus tax. It had a funny lid that quickly got removed and tossed in the recycling bin.  You might have luck looking at a discount store, culinary supply store, or maybe even a K-mart.  You will also need a lid, mine is 1/4" polycarbonate plastic of some type or another, can't be certain as it was free and unlabeled, but I have shot it with a 22 bullet, and it didn't break, strong enough for me!  If I had to guess, I'd say you can probably find something at a plastic supplier for under $10 and if you want to feel safer, buy something thicker, a 1/2" piece of LEXAN would be overkill, but it will work. The basic supplies are finished off with some brass fittings (a 1/8" to 1/4" coupler, two 1/4" pipe nipples, two 1/4" threaded ball valves,) and some Teflon tape.  All of these were picked up at home depot, if you don't have a HD around, I suggest a local hardware store, or lowes...wherever they would have these things in your area.  The ball valves cost $4.00 each, the fittings ranged from $0.77-$2.07 so figure on $13.00 with the tape. A Vacuum gauge.  The one in the picture was found online at a reasonable cost of $6.89 at F.N. Cuthbert Inc.  Like the name says, I'm crazy, so I hastily bought it, in hindsight I should have bought the 1/4" model which actually cost LESS, at $6.32, oh well, this one works, and is a little bit smaller so I can still watch my silicone easily. The model number on the one I bought was 9747214 One final item bought for this was a 1/4'' male quick coupler nipple that was part of a set at Harbor Freight and cost (on sale $1.99) now $2.99

OK, for those keeping track, so far this has cost a whopping $40 or so, depending on shipping and sales tax (grrrr!)  $50 including the purchase of plastic I have yet to make a nice gasket, so far I have used the semi stiff plastic gasket that came with the steel pot.  I will replaces that with a silicone RTV gasket very soon, but so far so good, This will pull 28" of mercury, maybe even higher, but the gasket is seriously lacking.   The pot I have built this around will hold a 1 quart container (32 fluid ounces) with an inch to spare at the top.  Due to this fact I have included the second ball valve.  This will allow "burping" of the silicone.  Air can be reintroduced by opening it and causing the silicone to collapse.  The ball valve connected to the venturi valve is a means of giving my small compressor's tank time to refill while maintaining vacuum, I bought it at Harbor Freight as well, and am slightly skeptical of it's overall quality (buy American, if you can find anything made here anymore, and if not, get a warranty.)

SO, it's time to build! First, I laid the plastic on the workbench, traced around the lip of the container to establish the size of the opening, then guessing where I wanted everything to be, and taking into consideration ease of operation and viewing, marked where my valves and gauge would be with a marker.  On a drill press, (or with a hand drill) I drilled out the openings for everything. I used a 1/2" bit for the ball valves, and forgive me, I forgot what size it was, smaller bit for the gauge.  You might want to test all your valves to ensure that they are air tight and operate properly. At this point, all major construction is done, you just need to wrap the joints with tape, and assemble the fittings and screw them into the plastic sheet.  Be careful on the vacuum gauge, as the case is plastic, only apply pressure to the brass stem.  I haven't detected a leak around the fittings where they screw into the plastic, but it IS possible, so I may apply a bead of silicone caulking to the exposed threads. That's pretty much it, I'm going to clean the plastic up, by cutting it down and cleaning any marker off of it, as well as building a new gasket for it, but like I said before, it works. A few technical notes, for the venturi vacuum valve to function correctly, it needs 4.2 CFM @ 75-90 PSI, if your compressor can handle this or better, you're in the clear.  If not, I would recommend that you either avoid silicones with a short pot life, buy another compressor, or use a smaller vessel to de-air in.  This chamber will hold one quart, which should safely de-air up to 1/3 quart (10.6 ounces) or possibly more with burping.  So far, there have been no implosions, but that's not to say they cant happen.  When in doubt, build it stronger and always wear eye protection. Just because I'm crazy doesn't mean I'm stupid!  If this helped you, send me money. Enjoy!