Demolded negative silicone mold, cleaned up edges using razor blade and tweezers. Note that for open-top silicone molds, it is important that there be no way for silicone to find its way between the part and the 'bottom' of the mold. Poured Smooth-On Task 8 heat resistant polyurethane resin into the mold, and it cured in around 10 minutes, getting quite hot in the process. The parts turned out as well as one could expect for a first attempt and a pretty mediocre silicone mold. The parts filed extremely cleanly. The parts did bulge at the open faces, but that is relatively easy to sand flat against a file. I noticed a small geometrical error and decided to design a full 1-piece mold-box combo for all the 3 parts, to be printed tomorrow.