Building Molded Parts
The first parts I started building were the molded sections of the prototype, starting with 3D printed masters.
The leg connectors are going to be solid aluminum. To create the aluminum parts, I 3D printed master parts out of plastic, adding Bondo and primer to bring it to a smooth finish and eliminate the striation 3D prints have between each layer. The toughest part of creating these parts is that they must be split down the center and mounted on either side of a match plate in order to be sand cast. Aligning the two halves was tricky but using registration pins molded into the 3D print managed to work well.
Part of the design includes bent sheet metal parts underneath the seat cushions and on the back of the backrest. For the prototype, these parts will be made of plywood and plastic and painted to mimic a powder-coated part. For the bent sections, I again created master parts on the 3D printer, primed and sanded them, and created an OOMOO mold around them. I then injected a two-part urethane into the oomoo mold (and was relieved to see the urethane uniformly come out all of the vents!) With the molds, I created five of each "bent metal" part. The cast parts are the same finish quality as the original master part, so the only sanding that will be required is where the vents exited the mold.