work on the principle of vacuum (or negative) pressure. Basically, a “bag” encloses a ski mold and the ski materials. Uniform pressure to squeeze
the ski materials together is created by using a vacuum pump to suck out the air. Figure 3 depicts a simple diagram for a vacuum press. Ski materials are placed on a bottom mold, then plastic film is placed over the materials and secured to the edges of the mold creating a sealed cavity. Finally, a vacuum pump sucks out the air to produce the needed pressure to squeeze the materials together.For the most part, vacuum presses are versatile, relatively easy to build and provide uniform pressure. However, the drawbacks are limited pressure (often low) and problems associated with wrinkles and bubbles in the vacuum film.
Sparknotes: The vacuum just replaces the top in this picture:
Taken from skibuilders.com
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