If you want to go cheap, I suggest you buy a used manual Knee mill or Drill/Mill, then replace the handwheels with your own actuators.
Knee Mills and Drill/Mills are available all ovr if you’re buying new from companies like Enco and Grizzly. But, you Ebay mavericks out there can find them for cheaper i’m sure.
Many handwheel pitches on manual mills are such that stepping motors can be used GEARBOX FREE for X,Y, and Quill axes (if you use the quill for Z) and directly mouted through a coupler (aquired from Helical for about 20 bucks) to the shaft the handwheels mount to.
However, if you want to use the Knee as the Z axis, you will most likely need to make a gear reduction, but shouldnt be anything above the 4:1 range… not too bad.
I suggest you use stepping motors for your axis drives since they are very very accurate and repeatable, not to mention easier to make your own controller for (if you are software inclined). I suggest you use the step motors available from Automation Direct. The NEMA23 doublestack @276oz-in torque should be fine for most X and Y axes, however some that will be doing heavier milling may need the NEMA34 @434oz-in.
Drives and power supplies for the motors are available here. Usually up to 2 (sometimes 3) motors can be run per power supply, and you’ll need one drive for each motor. The drives are pulse driven, one pulse in = one step… more on that later if anyone’s interested.
If you don’t want to make your own CNC control, then you have two options. One, the DeskCNC control provides a 100% deterministic control board and accompanying software… we’re going to use one of these controls to run a 15’x10’x2’ cnc machine.
If you want to run straight out of a computer… Mach3CNC from ArtSoftruns off of a PC. and controls frequency drive motors straight out of your PC. I dont have any experience with this but it gets good reviews.
Well anyhow, hope some of that helps… if anyone has any questions or want to talk more of the hardware side than control just post…