There’s a certain class of parts that just can’t be made on a standard 3-axis mill, nor with a 3D printer or a lathe. These parts — weird screws, camshafts, strange gears, or simply a shaft with a keyway (or two) — can really only be made with a rotary axis on a CNC machine. Sure, you could buy a rotary axis for a Haas or Tormach for thousands of dollars, or you could build your own. That’s exactly what [Adam Zeloof] and [Matt Martone] did with their project at this year’s World Maker Faire in New York. It’s the Rotomill, a simple three-axis CNC machine, with a rotary axis, that just about anyone can build. The design of the Rotomill uses a standard, off-the-shelf Makita rotary tool for the spindle, and uses leadscrews to move the X and Z axes around with NEMA 24 stepper motors. The A axis — the rotary bit — is driven through a worm gear, also powered by a NEMA 24. Right now this provides more than enough power to cut foam, plastic, and wood, and should be enough to cut aluminum. That last feat is as yet untested, but the design is open enough that a much more powerful spindle could be attached. The software for this machine is a bit weird. For most CNC machines with a rotary ax...