Making the Template

It took 2 weeks to make one half of the center exhaust runner wooden template on a milling machine. It looked excellent! I figured that rather than spend another 2 weeks, I'll just make a mould and then make a template out of fiberglass or some other material.

I had a bucket of polyfilla so I thought that I would put the template into an ice cream bucket and fill it with polyfilla. I coated the template with a paste wax and poured polyfilla to a depth of 2". First problem is that polyfilla isn't made for 2" depth. It bubbles, cracks and takes 3-4 days to dry. It has very little strength and broke into pieces when I tried to remove the template from the "mould".

The second problem was much more serious! I didn't seal the wooden template (with paint or sealer) and it absorbed the moisture out of the pollyfilla and swelled. Since the polyfilla was only on one side, one side swelled. The template warped!. Aggghh!

I dried out the template and glued and screwed it flat against an old 2" thick cutting board. Of course the template cracked. So out came the polyfilla to fill the cracks. I painted the template with some red spray paint I had around.

Next I decided to follow my original plan of using fiberglass as a mould material. After the paint dried I put on 3 thick coats of carnauba wax and started putting on the fiberglass and matting while the 3rd coat was still wet. Carnauba car wax is a release agent for fiberglass.


After picture - center exhaust runner fiberglass mould on left, wooden template on right.


Before picture - pouring fiberglass and matte on template to make fiberglass mould

The fiberglass mould needed work as it was rough in some places and there were air pockets. Out came the polyfilla and sand paper to smooth out the mould. After which I painted the mould red and put on 3 coats of carnauba wax.


Carnauba car wax - release agent for fiberglass among other things...

I mixed up another batch of fiberglass and used cabolic filler for strength. I poured it into the mold. About 4 hours later the fiberglass had hardened and the new fiberglass template was ready to be removed. The first thing I noticed was that the fiberglass had shrunk :-( It looks like it has about 1-2% shrinkage.

It popped out of the mould (not really, gently prying with a chisel) and is close enough in dimensions that I can use. Fortunately, I only need the general outline, as the critical sides are going to be machined off.

I mounted it and the wooden mould on each side of a flat 3/4" piece of plywood that was cut to fit the casting box shown earlier. Some minor touchup, paint and more carnauba wax and it'll be ready for pouring.

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Copyright July, 2011 Eugene Blanchard