Renishaw, digitizers

Hi to the list,

I just realized that I sent this directly to Doug, instead of the list.
I had another thought on the digitizer. What about just three balls,
equally spaced in an insulating ring. The "armature" would be a flat
disk, with three hemispherical cups, on the BOTTOM side of the disk,
arranged to register with the three balls. Slight pressure on top, with
a braided contact wire to ground. Long probe extends down through the
center. Now THAT I think I can easily machine (well, maybe the cups
would take some thought)!

This nicely solves the "centering" problem, solid armature, simple
design. Although I was intrigued by the problem of machining a "cement
breakwater"!

Alan KM6VV
PS, Is a ball end mill good enough to cut a hemispherical cup?