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.


Paper template


No bandswa, but a jigsaw did the job

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


Fins that define the foil

Then stuck them onto the plan shape


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.


Crappy expanding foam


Nice expanding foam


Just like shaping a surfboard


All looking good

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


In hindsight I should have done a few more coats


Almost ready for paint

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


All painted up but no where to go

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

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