"Ken Grunke" wrote in message
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Sure, although there are only two points of contact--one at the outside
edge of the hole, and then at the inside edge, where the 60 deg. cone
ends and straightens out to the pilot hole. I haven't done enough taper
turning to know--do those edges wear into the cone center after a while?

thanks,

Ken Grunke


Yes, they do, and in the process the shaft is constantly creating more and
more clearance between the centers as it cold flows to achieve the form. .
Look closely at centers that have been run offset to see how badly they are
deformed from the center drilled configuration. Further, if, when turning
between centers, if the face on either end of a part is not perfectly
square, it has the effect of creating an out-of-round (oval) turn. This
very concept has been the subject of endless debate, with almost no one in
agreement, but all it takes is a little experience in precision grinding to
put it directly into focus. Be certain to maintain right angles on the
ends of offset turned parts unless you don't mind oval turns.

Your ball turning is a very good concept, for it eliminates that problem,
but the same results can be achieved with center drills that are made with a
large radius in place of the 60° cone. DoAll is one of the makers, but
I'm sure there are others. They have a name, but it escapes me at the
moment.

Harold