Final Trivet

Last weekend we held a Pie Extravaganza as the theme for our annual birthday party.  (Molly & I have birthdays one day apart)  There had to be prizes, of course, so I thought that a pie shaped trivet cast in aluminum would be appropriate.  I originally planned to make 8 trivets so that each category winner would get one but time constraints and equipment breakdowns determined that there would only be one for the overall winner.  I thought I’d post the process for how I’ve been casting aluminum as well.

Rhino Trivet drawing

First, I draw the object in a CAD/CAM software package called Rhino.  I also set up instructions for cutting it out on the CNC machine.  The tabs are where the metal will enter and exit the piece.

cut out trivet

Cutting out the shape to be cast on my CNC machine (computer controlled router).  I use rigid insulation foam from Home Depot to make a positive copy of the shape I want in aluminum.

plaster trivet

The foam is dipped in plaster (actually drywall texture) to give it a shell that will preserve all the detail of the piece.  The piece on the right is cracked because I tried to speed up the drying process by putting it in the oven.  This whole thing is packed in sand mixed with bentonite in a wooden two part frame.   I cut sprues that align with the tabs on the piece  to allow the molten aluminum to go into the casting.  It vaporizes the foam instantly on contact and replaces it with metal.  Unfortunately I didn’t have a camera handy when I was doing the casting so there are no pictures of this part of the process…

Raw Trivet

This is how the casting looks right out of the mold.  The plaster just flakes off.  I cut off the sprues here and am ready to do a little finish work with a file.  I’ll also fill in the text with black paint to make it pop.

Final Trivet

The final product.  Snatched by a Key Lime “Pucker Pie”.