Assumptions and Presumptions

There are various sayings about “best laid plans” and “counting chickens” .. they seem to boil down to “if it can go wrong it will” or something like ..

I thought I had most of my ducks at least .. close to .. ready to .. align. Nope. It took me most of a day to get all of the items for my pressure tank assembled. Same with the vacuum chamber (another day, not the same one). A comedy of errors to some extent with runs to Harbor Freight, Ace Hardware and Lowes.

Pressure Chamber

Evidently, the slave labor in China that cut the pipe threads in the top of the Harbor Freight paint pot didn’t go any further than that .. there was a ton of trash from the threading. I purchased a set of pipe dies from Harbor Freight and cleaned up all the tapped threads followed by cleansers and air and a vigorous wipe down. Testing I found that the safety valve was releasing at about 35 psi. The paint pot is rated at 60 psi so I ordered a new safety valve from Amazon with a 50 psi release rating. Tested again and everything works.

Vacuum Chamber

This got weird. I have managed to lose the vacuum gauge, T-fitting, globe valve etc. that came with the vacuum chamber – have looked everywhere for it without any luck. Shrug. I ended up purchasing a Brake Bleeder and Vacuum Pump Kit .. JUST .. for the vacuum gauge. So .. finally .. got all the bits hooked and connected and I pulled around 28 inches of Hg ..

Test Mold

With everything ready it was time to test the system.

RTV – the first problem I ran into was the shelf life of the RTV I had. I had an unopened Mold Max™ 30 from Smooth-On. The shelf life SUCKS. The raw RTV (Part A) was more like creamy peanut butter than a pourable rubber. Since I had the stuff I decided to see if I could make a mold. Again .. the Part A was so thick that mixing with the Part B catalyst was like .. well .. mixing the former peanut butter and milk .. mostly sucked. I grabbed some items .. coins, a shutter, a crate and a fan. I managed to get the RTV into the mold box – which was more like pressing the (again) aforementioned peanut butter with a wood stick.

I took the opportunity to test my vacuum chamber to degass the RTV. This worked pretty much but took a good half hour. I am assuming that this was for two reasons – (1) the old RTV was too thick and (2) my 2.5 CFM Vacuum Pump was not pulling enough vacuum. I have a 6 CFM pump enroute and also so fresh RTV.

I was pleased at the quality of the resulting mold .. at least the part that will receive the casting resin.