I would like to start to make some pen blanks with the Alumilite clear, or the Alumilite clear slow. I have not made the investment of a pressure pot as yet. I have made a vacuum chamber using a converted air compressor and a large spaghetti pot with a clear lid. I am able to get 21 in. of vacuum but I am not sure if that will be enough to remove the air from the Alumilite. What would be the minimum amount of vacuum needed to work effectively?