SHERDILL

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iwould like to make a fiberglass copy of a plastic cowl.The plan is to make a plaster mold then lay it up with glass.The surface and seems on the plastic cowl are rough and will require filling,i was wondering what type of material i can use on plastic that i can sand to a smooth finish in order to use it as a plug...

Thanks

Campy

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" iwould like to make a fiberglass copy of a plastic cowl.The plan is to make a plaster mold then lay it up with glass.The surface and seems on the plastic cowl are rough and will require filling,i was wondering what type of material i can use on plastic that i can sand to a smooth finish in order to use it as a plug..."

I suggest roughing up the seams and other surface areas that are rough, then use some "spot putty" (red stuff, comes in a tube and usually found in the auto section of
Wal-Mart) to glaze over the areas. After it dries (usually 24 - 36 hours) sand it smooth (I start with 150 or 220, depending on how rough the surface of the filler is, then work my way to to 320 and finally 400 WET.

You want the surface to be as perfect as possible - that will determine the quality of the plug/mold AND the finished part.

After everything is dry, and assuming you will be filling the INSIDE of the cowl with plaster, you need to check a couple of things: 1. Make sure you put a circular piece of plywood where the engine shaft comes through the cowl. 2. Make sure there are no protrubences (things that stick out from the cowl). Then if everything is OK, apply a LIGHTCOAT of vasolene to the inside of the cowl (this is so you can get the plaster plug out afterwards), support the cowl so that it doesn't shift or change shape when the plaster is poured and pour the plaster.

Let the plaster sit in the mold for 48+ hours, then you can remove it. Let the plaster dry for about 2 weeks to get rid of the extra moisture and you are ready to go.

If you are making a mold from the OUTSIDE of the cowl, again, make sure of protrubences (if there are any make the mold in 2 or more pieces), then make a box to hold the plaster ANDsupport the cowl, lightly coat the cowl with vasolene and pour the plaster. If you make the mold in 2 (or more) pieces, make up your fiberglass pieces, then join together afterwards.

I vaccuum form a lot of my own parts and this is the basic procedure I use for making a plug from an existing part.

SHERDILL

My Feedback: (6)

Thank you so much for detailed instructions.I will be making the outside mold.How do i seal the plaster once its dry,some people mentioned they use epoxy or polyester resin etc.What do you use?

Thanks Again

bigtim

My Feedback: (13)

here is my project I have been working on for a while now I go into detail on how I formed a plug and made a fiberglass mold for my cowl http://www.rcuniverse.com/forum/m_56...tm.htm#5620546

but to answer your question simply use oil based glosspolyurathane, I brushed several coats on using a foam brush,but for a really smooth surface a spray can would be a good choice, after it was dry I waxed it up and made my part worked great.