The Excelsior Project, 9: Patterns & Molds

Mockup of the gas tank. Oil tank is the left side. The number 6 denotes the number of tries to get the shape right. It's pretty close here, and number 7 became the final version.

The patterns I gave the patternmaker have come back; molds taken from the patterns along the "split" lines are then mounted on boards to be sent to the foundry. These will be used to cast the struts and rockers for the front forks. The foundry will use these boards to make sand molds and then pour in 4140 steel. The middle lump is the "gate" where the molten steel enters, and the two uprights at the ends are the "risers" where the steel exits, but then flows back into the mold as the parts cool. It is definitely an art.

I can buy reproduction saddles like the one below, but I wasn't happy with the shape. Have you ever tried to ride a bicycle with the sides sticking out like that? Your inner thighs would get so chafed it would be unbearable. I decided there must be a better shape while still being true to the original. This is the start of the "plug" which the female mold will be made from. Pretty simple: a couple of 1/8" wires welded and formed into a shape.

To turn the wire form into a 3D shape, aluminum welding rod was bent and glued into the correct profile, masking tape applied over that, and the inside then fiber-glassed.

These are the two "plugs" before final painting. After paint, many coats of mold-release wax are applied before the mold is started.


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