I made the pattern out of poplar. It was my 4th or 5th try because I went into this with the incorrect assumption that bodgy wood work was okay. For the core I split a piece of PVC pipe on the bandsaw. Then I held the pipe together with hose clamps and packed it with petrobond and some nails.
This is the pattern I made. Pretty lame but it got the job done. I also machined the faces of it which revealed lots of tiny inclusions. No surprise since I didn't bother with degassing, although on one end it looked like the bubbles are radiating away from the core. I'll have to use hardened sand with a vent through it next time.
There's nothing lame about a pattern if it works... as far as porosity goes, I've had castings so porous you could blow air through them like a sponge. Even GM Australia had to vacuum impregnate their V6 aluminium engine blocks with resin to seal them, it caused problems when using propane as the fuel. A faster melt time if possible can help as well as not casting too hot, the cooler the melt the less hydrogen gas can dissolve in it.
I feel like as the son of a shop teacher my woodworking should be a little slicker The porosity isn't anything that would affect functionality and there's plenty I will be doing in the future to improve it. Like knowing what temperature the metal is when I pour it, or getting the proper tools instead of using a pair of tongs for everything. I'm just really stoked that I got this all working. It's been tougher to get going than I had anticipated but it's super gratifying.
