Fiberglass mold

Carl Ellis was kind enough to let me use his cowl bump to make copies in fiberglass.  Cowl bumps are needed to allow the use of shielded spark plugs, the shielded plugs are taller than the old style plugs and won't fit under the stock cowl.

The first step in making a fiberglass mold is to attach the original part to a plywood base.  I screwed the original to the plywood from underneath.  Then I coated the original and the plywood base with wax. Photo 1.  There's lots of great, expensive fiberglass mold releases and waxes available, but I used plain old car wax, the kind that comes in a can (Turtle wax).

Then I covered the original and base with a layer of fiberglass cloth.  I got my cloth and resin from WalMart.  It took about 1/4 of a quart can of resin to make the mold.  I used a cheap chip brush to apply the resin.  After the first layer of fiberglass I applied a second layer (right after the first layer, before the resin sets).  Then I set a plywood board into the wet fiberglass layers.  I'd cut out the plywood earlier so it would fit snugly down around the original part.  Finally I applied a third layer of fiberglass over the top of the plywood and original.  So I'd made a sandwich of: plywood base, original part, wax, 2 layers of fiberglass, another plywood, and a final layer of fiberglass.  Photo 2.

After letting the sandwich resin cure for a couple hours I used a putty knife to pry the sandwich apart at the wax-fiberglass boundary.  After mounting support rails on the second plywood piece I had the negative mold shown in Photo 3.

Link to Fiberglass Layup

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