This design slips on to the slide handles of your lathe or mill (http://machineryhouse.co.nz/L159 is the exact model used) and allows it to be driven by a stepper motor. This can be as part of a full CNC/computer setup, or a simple, repetitive task controlled by an Arduino. The drive gear is easily removable, and the motor is slack when not driving.
Print the gears, and melt the little one onto the last 8mm or so of a NEMA17 stepper motor shaft.
Print the bracket and fasten it to stepper with 2 x M3 12mm m/screws. Use 2x M5 16mm m/screws or whatever your lathe/mill takes to fasten the bracket near the gears. You may have to modify the positions or sizes of the slots for your lathe. You can edit the mesh direct or use OpenSCAD.
Connect the stepper, a driver board, and http://arduino.cc as shown in the diagram, and load the example PDE code. The motor should step back and forth a bit, then go slack. This will happen when you hit the reset button too. Change the code, add limit switches, push buttons etc from the Arduino Examples folder.
Fit enough of these to a mill and you can run it off a RAMPS board - instant CNC from a RepRap!
This project is an Open project for New Zealand's "The Shed Magazine"