Making a mold
The plug or buck is required first to make a mold. This will be an original art part that is to be copied. These days very accurate patterns can be laser cut or machined to very small tolerances by computer, then surface finished to make a high quality plug.
The buck or plug, however it is produced must be waxed with several coats of mold release wax and polished in between coats, before the mold may be made. Depending on the desired surface, PVA (Poly Vinyl Acetate) may be sprayed on as an additional mold release agent. However this will reduce the smoothness of the molds finish.
Once the plug has its release agent applied, gelcoat is sprayed or brushed onto the plug. Gelcoat is a pigmented resin without reinforcement. Tooling gelcoat is used for a harder more durable finish.
Molds are usually made from the same fiberglass the part is made from. A mold should be 5 times thicker than the part being made. Such as if a part is made from two layers of 1.5 ounce mat, then the mold should be 10 layers of 1.5 ounce mat. Hence, many layers of fiberglass will be applied, and resin added bonding the fiberglass layers together.
Once the final layers of fiberglass are applied to the mold and allowed to set up, wedges are driven between the plug and the mold to separated the two. When released you have a negative image of the original part, or female mold.
Making a part
The making of a part is the reverse of making a mold. The mold is waxed, and PVA is applied if desired. The mold will be sprayed with gelcoat in the desired color of the part, then layers of fiberglass are built up to the desired thickness. Once complete, wedges are used to separate the part from the mold.
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