After the sheet heats up to the point that it is sagging about 1 1/2" at the center, you carefully lower the frame onto the pattern (buck). As soon as you turn on the vacuum, the sheet is sucked down tightly. Leave the vacuum applied for about three minutes to help cool it and you're done.
Normally I wouldn't have gone to so much trouble to build a machine for just a couple of parts, but I do plan on making some trim pieces for the cabin with it when it comes time to do the upholstering.