Melty Plastic

By Charles T. Jackson

Now that we’ve discussed how to make a plaster cast, and all the parts required for a vacuum form table, the last element of the puzzle is the heating of the plastic and the “pull”. Like I mentioned in my last post, I tried my grill first as a heat source, and it did work, it just didn’t heat the plastic enough to get a “full pull”, meaning that I wasn’t able to get the plastic to pull all the way down to the table surface and capture all the details of the skull cast that I was using.

Vacuum Form Process
All of the successful home vacuum forming  videos that I saw on YouTube brought their hot media holders right out of their oven to the vacuum form table. I placed four ceramic mugs at the outer edges of the upper rack to keep the media holder up away from the metal rack, and placed my media holder on the mugs, making sure that they were as far out of the way of the plastic as possible. I then set the oven to broil which produces heat in the range of 450-500 degrees. In a surprisingly short period of time, I could see ripples forming in the plastic, and then the starting of the expected “sag”. When the plastic sagged to a point that I thought it was about to go molten in my wife’s new oven, with proper safety gear on, I started the shop vac, removed the media holder, positioned it over the cast, and pushed it down onto the table until I’d made a good seal.

In this particular picture, I have the old media holder, and a small Stinger vacuum in use, and neither proved all that helpful. There might have been enough suction if there had been a better seal, but I’ll never know because I made the new media holder, and not wanting to take any chances I powered up to the largest shop vac that I had. With the new media frame and the full scale shop vac I was able to capture all of the detail of not only the plaster cast on the table, but many of the exposed holes in the table itself. Fortunately I had seen a video that indicated that powdering your cast with standard baby powder makes it easier to get the cast out of the plastic. You also have to be careful not to try and pull anything that has deep undercuts, as it will very likely get locked into the plastic and stop your reproduction operation in it’s tracks. Learning how to do this was quite a trip. You see a lot of people try it in different ways, and have differing degrees of success. The common theme in all of the videos, like from negative experiences, is that you have to be very careful not to get burnt while engaged in the craziness that is involved in getting the softened plastic from the oven to the vacuum table. Commons sense, and some oven mitts really go a long way!! The next step of course is cutting the piece out of the plastic. I had initially tried using metal sheers for that, but it was nearly impossible. At the bad saw, the came out of the plastic very easily. In my next post, I’ll cover a setting solution that allowed stage room for massive numbers of kids in our Summer Youth Theatre production of “Little Princess”. Thanks for stopping by!!