The biggest enemy to resin is humidity. Here are a couple of photos of a vacuum chamber I built some time back. It was built out of a ten inch piece of PVC pipe I found in a dumpster at work. I added a interior LED light to better see what is going on inside. I use it to de air silicone before I pour it into a mold box and to remove humidity from my resin material. If you have attempted to try to make your own parts and the resin grows and starts to look like foam in a can it is full of humidity. Resin can reach a 160 degree temperature and the humidity will start to boil and foam up. After some time I bought a dehumidifier. After it was in use for 24 hours, the bucket was full. I could not believe how much moisture can still be in an enclosed shop even using air conditioning and also live in a dry state. A big problem with parts you may purchase that have dimples or warts on them might actually be from the silicone mold not having been de aired first. A silicone product may say that it does not need to be vacuumed but this is a CYA statement on their part. Many times I mix, vacuum and pour and vacuum again even on molds that are not very tall or thick, however you want to view it. Humidity and room temperature can effect the silicones ability to cure. I pour a small amount of silicone over a part with lots of detail like a wheel or grille or a dash and vacuum it. A small bubble can trap in detail crevices causing the part to come out with a wart on it. A small bubble can form just under the surface of the silicone next to a part too. Once pressure is applied that small area will get pushed in and a part can come out looking bad but to the eye the mold can look like there is no problem and from experience that can be frustrating to learn. Sometimes once the mold is inspected the problem is obvious but once it sets for awhile it can look normal again, A Jeckyl/Hyde affect. A air bubble tapped in silicone can be affected by normal air pressure too. if you notice a bump, stick a exacto knife blade in it to relieve the air pressure. The tubing you see has a drain valve attached to it. I usually just hold my gloved thumb over it so the vacuum draws down. The material will start growing and you want to make certain it does not go up and over the top of the container making a big mess. The front clear cover is about a half inch thick. I use a Robinair 2 stage 15500 vacuum pump. You can buy a 2 stage from Harbor Freight, but you should buy the warranty too, just to be safe.
