Since I had two handwheel patterns that were mostly usable, I decided to give casting them a shot today. After work, I glued up some feeders to the two wheels and dipped the foam in drywall mud. I had the mix too thin, so it took extra long to get the thing coated and dry enough to pour. I fired up the furnace and threw in the KHPT slug and sprue from the last pour. I also threw in a couple of the extra adjustment block castings and some chunks of lawnmower engine.
When the mud was dry enough, I put a couple inches of sand in the bottom of a new plywood box I made to pour in. Up to now, I've been pouring lost foam castings in a large galvanized tub. It works well, but it takes a large (heavy) amount of sand to fill it and for small parts like these, it just doesn't make too much sense. The new box is about 10x10x10" inside and workes perfectly. I nestled the patterns into the sand and covered them up, filling the box almost to the top. I used my cheapo craft store hotwire foam cutter to trim the sprue down to just above the sand. Then I used a propane torch to melt the top of the sprue a bit to form a pocket for the aluminum. The KHPT was placed on top and I was ready to pour.
Last pour, I had the aluminum too hot. This time, I think it was a little on the cold side. The wheels came out with a couple spots that were almost cold shuts (metal freezes before completely filling). The wheel's will work, but they could've been better. I need to experiment with adding vents to lost foam patterns to help the foam vapors escape...
All in all, it was pretty satisfying to see a project start on my computer and end up in (mostly) solid aluminum.
