re:digitizers

If three balls in three conical cavities are used to located the sensor rod,
things will be overconstrained. It is common in sensitive mechanical
devices to use a kinematic mount for this sort of thing: three balls can be
located with one in a cone, one in a groove, and one on a plane. Better is
the three groove technique; the balls sit in three grooves which are angled
to intersect each other towards the center of the triangle they describe.
the groove is wide enough that the ball touches the walls tangentially.
For sensitive systems carbide balls are used with sapphire plates, but that
obviously won't work for a switch.

I wonder what the hardest metalic conductive material is (that doesn't have
problems with oxidation)?

Elliot Burke