>I've been pondering the purchase of a CNC lathe/mill, but for
>cost reasons I'm going to do this incrementally ... pick up
>the basic machine first, then add on stepper motors and CNC
>capability later.  But I'm researching first...

Appreciate your question was specifically about the electronics/interface
protocol side of things, but on the mill side I believe Sherline make a
small unit with the motors et al, ready to add a controller.
http://www.sherline.com/ No experience with them myself, but they come
highly recommended by someone who I respect in his mechanical abilities.

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