00-Plastic_corn_halves_coated_with_release

Corn Mold Project

Plastic corn halves coated with release

What we have here are fake corn cobs, made of plastic. They are sliced
exactly in half down their parting line, and then nailed to a piece of
melamine shelving. A chemical called PVA (poly vinyl alcohol) has been
brushed on to act as a mold release for the fiberglass resin.The whole idea here is to make a pattern for an aluminum corn-cob
making mold. The finished aluminum piece that this pattern will produce
will be used for casting epoxy replicas of…you guessed it, corn cobs.
It’s a “mold to make a mold” project!
On an earlier attempt, I had used just resin and cloth against the

corn-kernel surface. This resulted in a lot of trapped air, and big
ugly voids. So as you can see in the picture, I smeared the cobs with
bondo to help fill in between the kernels to make a better imprint. It
worked.

 

Buttered with bondo for good surface reproduction

Now, on top of the bondo, I’m putting about 3 layers of fiberglass
cloth and resin, tucking it neatly down between the cobs. I used
aluminum duct sealer tape to form a dam to hold in the resin, which I
poured to about a quarter inch (7mm) thick.

 

Fiberglass cloth and resin coating

The PVA mold release now officially has my utmost respect. The mold
pulled free of the melamine, and the corn cobs pulled very neatly out
of the Bondoed cavities.

 

Resin and bondo cured, corn cobs removed

I used the bottom of a paint can to draw the radii of the corners, then
cut out the whole pattern with a band saw. The tab at the right end
will be drilled and used for hanging the corn molds on a pegboard hook
or something.

 

Trimmed and ready for touchup

There were still a few air bubbles in the resin, so I filled them in with Bondo putty as well, then sanded them down smooth.

 

Blemishes filled, ready for paint

I always paint my patterns with the obligatory “Dan’s
Workshop-dot-com-gray” paint (most accurately color matched of course),
acquired from my local Home Depot.Painting the patterns helps to spot any blemishes that might have
gotten missed. It also makes a nice slick finish for the molding sand
to release from. Stay tuned!

 

Finished pattern, ready for the molding bench

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