The existing Z axis acme leadscrew is retained into the Z axis carriage by a pair of 42 mm OD angular contact bearings, with the acme nut being fastened by a bracket bolted to the base of the machine frame. There is a set of crossed pinions that connect to the handwheel to rotate the screw and raise/lower the carriage. Because there is some backlash in the screw and pinions, and the fact that the efficiency of the acme screw is low, I plan to replace the screw and nut with a ballscrew.

While I have the machine dismantled I have measured the layout of the lower face of the Z Axis carriage, this is easier to do bottom side up, rather than having to measure under the machine. These measurements may be required when I design and fabricate the parts to hold and drive the ballscrew.
Attachment 405746

I have two ideas in mind:
- mount a pulley on the shaft inboard of the bearings at the top of the screw where it attaches to the carriage. The pulley will drive the screw. This will require some machining to the screw to cut off some of the threads and extend the bearing area, and a new motor mount plate will have to be fabricated. The motor will move up and down with the carriage.
- fix the ballscrew to the carriage to prevent rotation, and fabricate a bracket for a rotating ball-nut. This bracket will fix to the machine base along with the motor and the ball-nut will be driven rather than the screw. This requires a lot more machining so is the second choice.

However these are just preliminary ideas that are parked here while I finish the X axis modifications.