My next Camsoft project is going to be lathe. I have a 15" LeBlond manual lathe that I would like add some CNC capability to. I also want to completely retain all of its manual capabilites (ie easily switch between manual and CNC mode). I am just now beginning to think about this, and the following questions have come up:

I do not want to change the spindle motor to a servo, so can I put an encoder on the spindle to allow inches per revolution feedrate programming? Would it be hooked into the main encoder on the last axis, even though there aren't going to be any servo connections?

Is it possible to use the LeBlond Z axis feed (no servo) and have the X axis servo react to the current Z location, almost like an electronic tracer?

Assuming the answer above is NO, as I expect it will be, I can see three options for driving the carraige.
(1) putting a servo on the feed rod (disengaging it from the QC box when in CNC mode) and using the carraige spur gear and rack as in manual operation.
(2) putting a servo on the leadscrew and engaging the half-nuts when in CNC mode.
(3) adding a servo driven ballscrew to directly drive the carraige.
Even though I am going to have linear scales, I believe (1) will have too much backlash to be a viable option. There also isn't an easy way to temporarily disconnect the rod from the QC box. (2) would be OK if I don't run in CNC mode much and don't mind the additional wear on the nuts and leadscrew. (3) is probably the best choice, but would require the most work to implement and be cumbersome to change between manual and CNC modes.

Anyone have any thoughts or words of wisdom?