This is a short video of my CNC-converted Grizzly Mill-Drill (Sieg Super X3) being used as a lathe to cut a switch knob for a PDP-7 computer. A 3/8″ 6061-T6 aluminum bar about 3″ long is mounted in a collet in the mill, and is driven past standard lathe tools mounted to the mill table. The spindle is running in reverse direction due to the orientation of the tools. I created a G-Code program by hand to make the two different tapers and cut off the knob at the end. Depth of cut was .010 because heavier cuts caused the rod to deflect too much. Spindle speed is about 800 RPM; cuts were made at 3 inches/minute except for the final cutoff, which is about .3 IPM.
I was fortunate enough to see the PDP-7 in Paul Allen’s vintage computer collection (yes, that Paul Allen) at PDP Planet on a recent visit to Seattle. Very cool stuff!