It was cool to watch the Tormach hog this out of a block of aluminum bar stock.
A PCB will bolt onto this. Some parts will be on the bottom, and will get hot, so we'll use gap-pads or thermally conductive putty to conduct the heat down to the block, which will itself get cooled somehow. Some of the cutouts are clearances for the pins of thru-hole parts.
This was hard to photograph; the shiny features mess with my camera's autofocus.