Posted by: Mike Randall | April 5, 2009

Centre Board – Casting Pattern

The centre board for the Stir Ven is specified to be built from cast iron!

Jezzus! I won’t be doing that in the backyard!

The last thing I cast was a bad skull ring in year eleven art class using the lost wax method! My skull looked more like a blob than the Phantom ring it was intended to be. Hmm doesn’t bode well!!

Anyway this all sounds a bit daunting so I guess I’ll start with making a foundry pattern! Most sensible people would discuss this with the foundry that is eventually going to cast the thing. Not me though, fool I hear you say! Any ways I researched as much as I could on the internet and decided to just get stuck into it.

The plans give all the info needed for the foil shape and all the other dimensions. Here’s a bunch of pics showing what I did.

Following the plans. I drew up the shape on my computer, and got this printed out at the local Kwik Kopy. I glued this directly on to some MDF, then cut it out with my jigsaw.

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Paper template

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No bandswa, but a jigsaw did the job

Next I cut out lots of dividers that define the foil shape.

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Fins that define the foil

Then stuck them onto the plan shape

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Fin and spine in place

To fill in the gaps I used expanding foam, then shaped it back with a surform and coarse sand paper. The gap filler stuff in a can from the local hardware was not really the best choice as it left to many air holes. So I got proper moulding foam from Dalchem, it’s basicly two part buoyancy foam you get from most marine stores.

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Crappy expanding foam

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Nice expanding foam

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Just like shaping a surfboard

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All looking good

Once everything was shaped up I painted it all with epoxy filler, then car body filler.

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In hindsight I should have done a few more coats

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Almost ready for paint

Finally I filled and sanded, filled and sanded, etc etc… then enamel coated the whole thing.

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All painted up but no where to go

It is now ready to go to the foundry… (to be continued)


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