On Aug 8, 8:07*pm, Joseph Gwinn wrote:
I recently got interested in what Franklin Hardinge, a founder of Harding *
Brothers, the predecessor of the present-day Hardinge Company, had invented.

1. *US Patent 894,634 "Lathe", to Franklin Hardinge. *This is probably his
original headstock design. *The key is to have thrust bearings (ball bearings)
independent of the axial bearings (cast iron sleeves with a precision-ground
spindle within). *The cast iron sleeves are tapered, and one can adjust the
running clearance quite precisely by moving the sleeve, without dange of jamming
the spindle.

It's also interesting that the thrust bearings were on the distant end
of the
headstock, not near the nosepiece. The thrust was first coupled to
the
pulleys, then through the balls to the cast iron. That has the effect
of
making any thrust-related deflection happen far from the working
end of the spindle.