Here is a link to some info that will help you,
www.cnczone.com/forums/bridgeport-hardin...cnc.html#post1839270
when I did the conversion I planned to do a proper write up for it but have been too busy and never got to it. Below are a couple pics of what I ended up with for the power supply. I get about 65 volts to the motors and that is good for a reliable 100 IPM on my machine. These machine with the stock steppers will not perform well if you turn up acceleration but do work good enough for a home machine shop.
Edit, I added the pics and wiring info that I have to photo album linked on the first page of the post.
