This was a project for a ball turning tool as a Quick Change Toolpost accessory.  I wanted to be able to switch to ball turning with a minimum of changeover time.  The inspiration for this was a small shop-made offset boring head with very small slides and a pinch clamp arrangement for both gib adjustment and slide locking.  Only about 2'" to 2-1/2" per side it was a dear little tool.  This ball turning accessory is also designed around a standard boring tool as a cutting bit.  The up-and-over ball turning process has the cutting tool cutting on the end, tangential to the workpiece so a standard boring tool provided side clearance already built in.  the end of the bit was re-ground for rake.  Slide travel is a nominal inch, which with second offset mounting position for the cutting tool provides for a maximum ball size of about 4".