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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!

Buttered with Bondo for good surface reproduction

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.

Fiberglass cloth and resin coating

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.

Resin and bondo cured, corn cobs removed

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.

Trimmed and ready for touch up

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.

Blemishes filled, ready for paint

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.

Finished pattern, ready for the molding bench

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!