Hi,
Myself and brother Dave, bought a Bridgeport J1 head about 2 yrs ago, fitted it out with steppers on 3 axis 70v 7A drives, (Z knee) and all work a treat.
We changed the original 1HP motor for a 2 hp motor driven by an inverter, driven by Mach3 PWM.
Ball screws on X & Y (metric on x and imp" on y).
X Y 1:1 ratio.
3:1 Z ratio.
Well, success today, our first "real" job.
OK, its only a cutout for a mains IEC connector, but it was a perfect fit!

We hit the start, Mach started the spindle and after a delay, proceeded to mill out the profile.
When finished, moved to a safe home position and stopped the spindle.
Now we can't wait to see what it can really do.
We are both very pleased and supprised how well the knee axis works, we did wonder if it would move at all! A 7NM stepper, 70v and a 7A drive is more than enough, without counter balance too.
The to do list includes, ....final connection of the coolant solenoids for mist and flood, connect the second inverter to the coolant pump and fit limit and home switches. I'm sure we will go overboard on the design for the brackets for the limits, just because we can. . .now!
Mach is absolutely superb, the forum is great and can't wait to make a mountain of chips.
Best regards,
Derek and Dave.