2. A collar
I also wanted a little collar to protrude from the center of the pulley. A grub screw will go through the collar to keep the pulley attached to the shaft. Here I'm sawing out a square of wood for the collar.
I also measured the thickness of the cut made by my saw, because I
thought I might need to saw the wooden pattern in half (to make it
easier to extract from the mould) and so I'd need to compensate for
the thickness lost during sawing.