Operational, as a CNC mill. Replaced Y-axis drive threaded rod, spring-coupled left-side lead screw to allow for manufacturing tolerance, bolted down MDF surface, installed limit switches, and attached David Crocker’s differential optical probe (https://miscsolutions.wordpress.com/mini-height-sensor-board/).
Repeatability, as measured by the Z-axis optical probe, is a phenomenal 3 microns 75% of the time. Even more amazing is that applying a 1lb load to the middle of the X-axis causes it to sag <15 microns. Probing a row of points across a glass surface set on top of the MDF bed yielded values within 50 microns, and non-spurious values within 25 microns. All four corners of the Y-axis surface are equidistant to the rigid table underneath the machine, within 250 microns accuracy. Better tweaking of the anti-backlash nutblocks will probably give better repeatabiltiy.
Also, the Duet is proving by far the best CNC controller on the market. Highly recommend it for speed and versatility. Use of SD-Card G-Code scripts for a variety of configuration options, including homing sequences, is especially powerful.
Next step is to add extruders, lasers. Time permitting and necessity motivating, full mesh leveling support may be added to the Duet frmware as well.