Brother TC-211

Meanwhile someone has used closed loop steppers. Their argument was it is cheaper and easier to maintain (if one of the original motors failed for example), replacement steppers being easier to source.

I doubt that closed loop steppers are adequate for this type of machine tool , not because of torque or speed, but because they can't support index home . Therefore you can not set up the job on the mill and turn it on next day and have precise machine position you set the day before.
For now I plan to use the original drives , if one goes bad it will be replaced with ac servo drive and motor (we use Xinje servo drives and motors as replacement for other machines if needed).

youd need to get better limit switches, but steppers would be fine. inductive switches can home well within a thou.

ill be waiting to see how using the stock drives turns out for you. for me, the stock sanyo drives wound up not tunable. the 211 uses Toshiba though, so maybe they will behave differently.

What size inductive proximity sensors give the best resolution? I have seen M4 & M12 on ebay.

It might also be dependant on target distance and shape

How did you wire the relay board? Relays have common +24Vdc so it needs GND from 7i77 to activate ?
Had same problem before, on Hurco MD1 so I adapted the relay board to use common GND.

this is mine first movement after rough tuning just to get things started