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making wheelpants and other molds

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Well-Known Member
Sep 15, 2006
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Jerry posted this website in another thread- http://www.geocities.com/mhammersmith/pants/pants.htm

It's actually pretty good but there are always more tricks that can help.

This guy's method to build a fiberglass mold uses epoxy which has the advantage that you don't need to wear a respirator but the materials are far more expensive than polyester resin. That is more typical of mold making. For a polyester mold, you would follow his waxing instructions, then spray tooling gelcoat (available in red or black) somewhere around 18 mils thick. Tooling gelcoat is specially formulated to make durable scratch-resistant female molds with little print-thru of the glass fabric or fibers. Next, follow up with fiberglass and polyester resin. It is completely unnecessary to spend the money on fiberglass cloth for mold making. Fiberglass mat will work just fine for a fraction of the price. You can stiffen the mold with coremat. A typical mold I would make for a sizable part- (16" canoe for example) would be tooling gelcoat, 2 layers of 3/4 oz mat, 5 layers of 1 1/2 oz mat, and then 4 mil coremat and 2 more layers of 1 1/2 oz mat. This ended up with a fiberglass mold about 1/2" thick that you could make scores of parts from. Since wheelpants are substantially smaller than a 16' canoe, you could skip a couple of layers of 1 1/2 oz mat and/or eliminate the coremat steps.

One more great trick I learned from a kayak manufacturer in Wales is as follows. Take your completed plug and completely encase in in a fiberglass mold before splitting it. Then build two plywood flanges about 2" wide that fit around the spot where you want to split the mold. Bolt together the two flanges with a series of bolts with a washer between the two plywood layers. Glass both flanges to the mold as one assembly. After the glass has set up properly, remove the bolts and washers and run a narrow blade between the plywood layers to split it. A fine tooth metal cutting sawzall blade would work well. Now wet sand the cut edges to remove nicks. To build a part from this mold you have two choices. You can build one half in each mold but do not remove them. Instead bolt the two halves together and seam tape the inside. What you accomplished is matching up the two halves perfectly so that you don't have to do alot of bondo work after to get your wheelpant or whatever to look good. You would just wet sand the part line. The other method would be to assemble the two molds and build the part in one shot through an access hole (for instance the hole where your wheel fits in the bottom of wheelpants).

The second method is a harder lamination to do but has added strength and less weight in that it doesn't involve a seam tape job inside. You would need to be pretty experienced with fiberglass to pull it off.

The above split mold is how the kayak manufacturer joined his deck and hull molds together perfectly for seam taping.

Your fiberglass parts will only look as good as your fiberglass mold and that will only look as good as your original plug so you really need to detail that out. I could write a full chapter on that. Also if you wanted to vacuum-bag parts, you need a flange on the mold to install a bleeder system and seal the bag so the flange is already built in the above method. Vacuum bagging is really slick (no odors except for a few minutes in the beginning) but that is a pretty invoved process. If anyone really wants to try it, I have done quite a lot. First you need to do some reading.

The fiberglast.com vendor is a good one although you could beat the prices with a bit of digging. I do use them at times.



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