Counterweight test bar for headstock alignment

[tonyfoale]

The bed of the lathe has a geometry that should hardly let it twist and moreover deflect (see attached picture). The calculated deflection with a force of 200N (eq. to 20.38Kgf or 44.93lbf) exerted in the middle (between the feet) is far less than 0.01 mm (0.000394") while it could twist by ~0.03 mm (0.00118") under a torque of 1000Nm. So I don't think the bed of the lathe could deflect of any meaning amount for that small weight (the whole bar weigh less than 6Kg (<13lbs)).

I was not thinking so much about the bed but about the head relative to the bed. You have stated that practice and theory do not match, therefore there is something lacking in your theory.