[ger21]

You might want to look at multiple start acme rod. I got 1/2-8 2 start (4 turns / inch) from MSC for about $22 for 6 ft. This will get you 100 ipm at 400 rpm. It will also work a lot better than plain threaded rod, and it's pretty cheap. For about twice the money, you can get 1/2-10 5 start (2 turns per inch), which will double your speed, but you'll probably need more powerful motors. If you really want to go over 100 ipm, you're probably going to have to start spending some money.

Gerry