I assembled a Rotary 4th axis that looks almost identical to yours here. My ShapeOKO 3 didn’t have the driver ports to control it, so I ended up swapping out the controller for a Teensy/GRBL-HAL replacement with 5 independent Stepper Driver ports - XYYZA is now my config. This setup also gives me limit switch capability on all 5 axes too, so my rotary has a proximity zero sensor - Nice.
I rely on the 2 Y steppers to hold the gantry ‘rigid’ during rotary work, and only XZA axes are actually moving. Some advice I read said the Y axes need physical locking to resist the cutting forces, but so far that has not proven necessary in my use.
I align the headstock and tailstock using an aluminium rail bolted down to the machine bed, and the underside of the headstock and tailstock have a channel milled in to a tight fit onto this rail - keeping them both exactly, or near enough, aligned.
