The basic theory of vacuum forming is simple. You simply heat a piece of material to the point that it becomes pliable then immediately place it over a mold and suck the air out. After the material cools, which isn't long, you can remove the material from the mold.
Despite their simplicity, vacuum form machines can cost several thousand dollars. Big machines will cost $60,000 or more and large custom machines will cost more than Uncle Fred's house at the lake.
A few years ago the creator of our plan sets made a wonderful little machine that employed a simple "2 Stage" vacuum system. Most other machines, including many small industrial machines use vacuum cleaner motors as the only source of vacuum. Some very expensive machines use large tanks to hold vacuum until it's needed. The little Hobby Vac used TWO sources of vacuum. The primary source of vacuum is your home or shop vacuum. This stage removes most of the air in the mold chamber. This is what most machines will do anyway with their vacuum cleaner motor, but the Hobby Vac went one full step better. The Hobby Vac also used a secondary vacuum pump. A vacuum pump creates high vacuum which is needed to pull fine details out of your mold.
This approach really makes sense. If you were to use a vacuum
cleaner motor alone you would never be able to reach the
high vacuum needed to produce excellent detail. If you were to
use a vacuum pump alone, you would need a very large tank
or very expensive vacuum equipment to evacuate air out of the
mold area. With the two-stage system you use the best of both
systems and save money by doing it.