The first mould(right) didn't turn out great. There was an air bubble that got trapped and some silicone flowed under the pulley. I could have cleaned this up but the imperfections of the printed/lathed were really obvious in the mould.

I printed out a second pulley and used the Dremel as a lathe rather than the drill press, which made for a much cleaner part. The void in the middle is the pulley, and the second try is on the left. The second mould is really good, time to cast the first pulley!