For a quick and dirty example I have formed a static spinner over an existing aluminum spinner. The pic below shows the spinner placed in the center of the box ready and the vacuum is connected. There have been many discussions on what temp to set the oven for different types of plastic. Personally, I always put the oven on broil and place the rack right in the middle of the oven. Let the oven get hot and then place the frame/material and cake pan (or whatever you're using) on the oven rack. Oh yeah, you will want to put some gloves on for this too! Now, leaving the oven door open, watch the plastic closely. You will find that nearly every type of plastic will do three things:
1. almost immediately it will pull up taught
2. some moments later it will begin to smoke
3. shortly after starting to smoke it will begin to sag

Once it begins to sag it is ready to form although different materials and thickness will require different amounts of sag. If you form to soon you run the risk of the plastic cooling before the part is completely formed. Wait too long and it may tear or, most aggravating, it is prone to forming webs. Webs occur when the hot plastic folds onto itself in which case it will not form properly around the mold. I have found no way other than trial and error for getting the hang of how much sag is required.