My Eagle 10x50 CNC mill started out life as a 2 axis machine and of course I can't leave well enough alone. So it needed a Z axis. So the question was: What is the best approach? The machine is a manual/CNC machine and I wanted to keep the manual quill capability with a quick change over. So the following is what I came up with. (I also upgraded the controls, which I'll post in another thread.)

Most Z axis conversions involve adding a ball screw to the quill. There are two problems with that IMHO. 1; you wind up with a big ugly box on the front of the head, and 2; it is not easy to disconnect for manual operation. I took a different approach.

First I took some pictures of the head, imported them into AutoCAD and just stared at them for awhile until some ideas began to jell.

Here is the working concept I imported a drawing of a NEMA 34 stepper and moved it around until I found a place that would fit and be out of the way. I tried to find a timing belt combination that would work, but finally settled on a gear train. I'll address the backlash issues later.




To install the new system, a little surgery needed to be done on the head. So I stripped the head down and borrowed a friend's mill to do the work.




I also located the mounting holes for the gear case. Mounted to an angle plate in this pic.




Then I made a new quill stop. This serves three functions: A quill stop for manual operation, a mount for the magnetic encoder readhead, and an attachment point for the anti-backlash system.



Renishaw 1 um magnetic encoder install




Making the prototype gear case out of MDF to confirm the tool path and to be able to test fit the components




And the finished prototype This is made from 3/4 MDF, the real gear case is 2 inch thick aluminum.



And it fits



The stepper motor clears as planned. Allows tilt to 45° in each direction.




The quill shaft to gear adapter.



The gear is attached with soft machine screws to act as a shear point in case of overload > 150% (just in case the operator does something stupid)



The next operation is to machine the gear case cover. It's bolted down to the to the gear case blank.


And the finished gear case cover along with the disengage cam and motor outboard bearing retainer.



Pocketing the gear case




And finished with the outside profile.




Starting to take shape. The center gear set is on a cam so it can be disengaged from the quill shaft gear.



Shown disengaged. The gear always stays engaged with the motor shaft.



And the parts fresh out of the dishwasher.




The anti-backlash system. The cable is about 1/2 of a Yamaha Banshee brake cable. This puts an adjustable upward counterbalance on the quill and takes out all of the backlash by preloading everything. It set for about 50lbs of upward force.



The other end of the cable is connected to a 1.563 air cylinder, regulated at about 30 PSI.
The Z axis consistently holds +/- 0.0001. To disengage the drive, just flip the lever to the other position and turn off the Z axis in software and you have a manual quill.