Molding and Casting

For this week's assignment, I thought about doing embedded LEDs, which I may yet do with my project, but I wanted something practical to use with my final project, so I made my electronics box.  It is very similar to the electronics box of the commercial model, but somewhat wider to accomodate the extra width of the OSMC motor controller, which is quite large for a motor controller (I was thinking of redesigning a surface mount osmc board, but this is most likely a down-the-road project).  Note: MIT's Project Orca team appears to have done this already.

Ok, so my box was a little large to use with wax, so it had to be cut out of polystyrene foam, which is the Devil's own child.  Here are some pictures of me milling out some test squares on the Shopbot.  I designed all my parts in Solidworks, saved them as STLs, then generated a toolpath in DeskProto, a fully-featured trial download of which is available at their website.  It's a pretty slick piece of cnc software, and allows you to vary a host of parameters, including estimating the machine time. 



Now once I finished making my two-part halving mold, a tried to find ways of sealing the foam.  First I tried gesso, of varying thicknesses/# layers, but this didn't want to dry because of the porosity of the foam; then I went to spackling paste, then a combination of the two, then a combination of the two with shellac, then all three with a layer of wax and mold release.  The foam was damn finnicky.  I got it to work, but only technically.  My mold was pretty much destroyed from the heat of the setting 325 urethane plastic I used.  Here are some pictures, both of my test sealings, and of the mold coming together/afterwards: