Casting and Molding

Week 7

It's funny, having spent so much time trying to replicate the look of rubber and plastic with paints, finishes, etc. in industrial design school for so long, it really blows my mind how simple it is to make the real thing.

This week is casting and molding and I worked with Will Patrick in the beginning to help document a tutorial Sam put on while the second half of the week was dedicated to making a molded plastic version of my motorcycle from the 3d print week.

The shopbot is surprisingly easy to setup for 3-axis milling. Using Partworks 3D and the few-step tutorial online, it was pretty much a no-brainer and the only kink in the road was tricking the software a bit by telling it my material was half its size so I could do a double-sided mold on the same block.

It was super painless and simple and the only new move is to re-zero halfway up the y-axis after the first mold and then bandsaw the two halves apart.

The wax molds came out beautifully. I was initially worried the ball-tip bit we used would smooth out my nice angular geometry but it didn't at all. Because space was tight, I ended up blowing out a few walls of the mold but after taping a few pieces of acrylic to the sides we were good as new.

The casting room was freezing, which is why I suspect the oomoo silicone mold took 3x the stated 75min curing time to actually stiffen.

Initially I wanted to put registration marks in to help line up my parts but I ran out of space and the oomoo was still too soft to machine reliably, so I just went ahead and dove into pouring each half separately.

Sam had brought in some really great Smooth-On urethane plastic and black and white dyes to play with so I opted for black. The pot-life is only 2 minutes so I had to work quick in mixing in pouring.

The cast parts came out amazing and still thin enough to glue back-to-back without much trouble. I did have to go in with a sharp knife and cut out the outline as well as re-punch the holes for the wheels' forks.

Plastiweld didn't seem to bond this material at all but Leigh had some super glue that (predictably) worked well and once the whole chasis was patched up, I laser-cut some press-fit forks for the wheels (a mess of undercuts made this impossible to do in the two molds without flattening a side).

A touch of WD-40 on the shaft bearings and now this thing zips along my desk!