This is a close-up view of a molded grill immediately after a well-used silicone mold is opened. The grill tendrils are all beautifully shaped, but all of their edges show major “flash” at the mold line. This flash consists of epoxy and carbon-fiber that have squeezed out of their proper channels while still in the mold.

Home-built silicone molds are simple and inexpensive to make, and allow beautiful, precise and extremely strong parts to be made in a small shop without fancy tools, however they have an extremely short lifespan. The highly-reactive hardener half of the epoxy goo slowly eats away at the mold surfaces, eventually creating gaps that grow, causing the thickness of the flash to gradually increase until the mold has to be replaced after just making 25 parts or so. 

The mold is filled at the end of the day and opening it first thing in the morning, before the epoxy is fully cured. The part is still flexible, but the flash is still soft enough to be easily trimmed off with an Xacto knife. After de-flashing, the still flexible grill is put back in the mold to keep the right shape until the epoxy fully hardens.  And woe unto anyone who forgets to de-flash a grill before the epoxy is fully cured.  After that, the flash will have hardened into a nasty carbon-fiber reinforced knife edge that eats Xacto knife blades and carbide de-burring tools, rubber gloves and finger tips to shreds. The flash then yields only to a high-speed carbide bit on a Dremel tool, which stinks and throws nasty carbon-fiber micro-splinters in all directions for the several hours it takes to clean up those 180 holes.

However, to end on a positive note, there is one joy in a new silicone mold - the first couple of grills coming out of it have flash so incredibly thin that it can literally be blown out of the holes as if it were cobwebs even after fully curing. When we can afford a proper hard-metal mold, all of the grills will come out even nicer than this, and life will be good.