I have a Bridgeport manual mill which i converted to CNC with servos, CSMIO control etc and ball-screws on the axes.

I now have a really nice lower half of a CNC with good positioning accuracy and the large table i like plus lots of easy access and so on.

The downside is the spindle/head - this is poor TBH and rattles (dog clutches gone) plus there is a vibration (maybe a bowed spindle spline but runs true at bottom.) The spindle is a QC/BT30 with drawbar.

The knee is currently my B axis and is coded in Mach3 to take tool length compensation.

My question is this - is it practical to rip the whole head off from the swivel ring on the base column upwards, bin it, and build a proper CNC Z axis to bolt on in its place?

I am thinking maybe a steel plate weldment with HiWin rails, servo motor plus an ATC cartridge spindle - this would remove the wobbly/weak knuckle joint and give a decent Z travel which the BP lacks badly in, it will also remove the Quill, splines, clutch and so on from the drive.

I currently have a large 3Hp AC motor on her, running 1:1 toothed belt under VFD/program control but that only gives me 4000rpm so would like some more. Maybe fit a 3kw (or more) AC servo drive.

I can't fit a "proper" cnc in due to a low roof and low power(home shop business) so looking to mod the old girl if it was a viable proposition.

Any tips much appreciated as always.

Thanks

Dave