Jazz,

sorry if I'm getting this completely wrong, but the op wrote a gearing ratio of 2:1, but also has written and drawn a 32 tooth pulley on the motor and 16 tooth pulley on the screw. Doesn't this setup actually give him a 1:2 ratio, so 1 turn motor gives him 2 turns screw. So theres plenty of speed, which isn't needed as you say 1:1 is ample for aluminium, the op's main working material.

Adil