I'd like some educated opinions on whether I am asking for the impossible (at the DIY budget price-point, anyway) as far as my motion controller requirements for a small slant-bed project. Basically going for a low-rent miniature Tormach-type slant bed, with a servo controlled spindle/4th axis suitable for light side-work (threading, keyways, slots, engraving, that sort of thing), that gets its G-code from an Ethernet line to a laptop (probably running Mach3 or 4). If not impossible, I would also appreciate any recommendations for motion controllers that seem to satisfy my machine requirements.

The source of my confusion over which/any controller to choose; my lathe spindle is a servo drive, the axes motors are steppers. From what I understand, it is rather impractical to drive a max-4000rpm servo spindle via step & direction input, but that seems to be exactly what is needed during the slow-speed 4th axis maneuvers. Further, it seems like the go-to options --such as SmoothStepper-- are only good for step/dir outputs. My servo-driver is an analog Baldor unit, which can only take step/dir (position control) or -/+10V analog (torque/velocity control). Is it reasonable of me to seek an "all in one" motion controller that can output the desired step/dir outputs to the spindle & axes, but is also able to control the spindle via 10V analog for velocity control? Some of the controller cards out there have a 0-10V analog spindle output option (Hicon Integra), but would I be locked into choosing one or the other spindle control method, and is there a solution for getting reverse-rotation if I go the analog route? With encoder feedback, I understand you can't just flip the motor polarity via relay & expect things to not go haywire.

Another possible 'solution' that I thought of was to leave the servo spindle in step/dir mode always, and adjust the electronic gearing parameter (set inside the servo driver) for fast operation to obtain the desired higher RPMs for most turning operations. Again, I'm not sure if this is something that is generally adjustable during a program, or must be configured manually each time (I haven't been able to figure out whether the Baldor/ABB "MINT" drive software is capable of this for sure). A sort of "electronic manual transmission" to modify the "electronic gear ratio" for each speed regime as needed.

For reference:
Servo Driver is a Baldor Microflex 9A analog unit
Servo is a Baldor BSM80C motor with 2500-line encoder feedback
Stepper Drivers will be Gecko or some other reputable brand
Stepper motors will be lower-speed NEMA23s in the 400oz-in range
I'd *like* to use a single motion controller card/unit connected to a laptop w/ Mach via an ethernet cable, that interfaces with the motor drives & feedback data as needed
--if required for accurate Z/A axis coordination, the Z-axis stepper may end up with some kind of closed loop feedback
--I'd *like* to keep the controller cost below $500-600$ USD unless there is some significant advantage to be had

TCB