Agree with every thing said above, especially about having enough air. The best sand blaster in the world wont be any good without a very high working air pressure. After sending my tub and frame to two sand blasters, I had to finish it myself. The small gravity feed ones work ok for small parts and are very frugal with sand. The pressure pot works much better for big jobs, but hog the sand. I was very luck to have a good source of high quality blasting sand nearby but I still had to sift it as my worse trouble was clogs from debris (larger stones, cigarette buts). I found out why paying to have it done is so expensive, its worth it because it sucks and uses a lot of sand. I went through over 1000lbs to do the underside of my 80 on a rotisserie.