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BottleBob

wrote:
On Aug 17, 5:57 am, BottleBob wrote:

If the electric edge finder is spinning, AND if it runs out a little,
it will probably light up when the high point contacts a conducting
surface. But you really won't know if that high point is .0001",
.001", or even .010" off center. That's why I would contact your part
with the edge finder stopped (then zero out your axis), back off your
part, turn the edge finder 180 degrees and contact your part again to
see if there is a difference in the two positions of the edge finder.
Half that distance difference should be your off-center runout

I don't want to sound nit-picky about this but to be really certain
about the effect of excentricity of the edge locator, the 180 degree
turn-around test described above would need to be repeated at 90
degrees from the first tests. Unless, of course, you were really sure
that at the first trial you indeed were at the high point of any
excentricity.

Wolfgang:

You wouldn't need to know, or be, on the maximum high point of any
eccentricity to average out the runout in one axis. Let me try to
explain it this way. Let's say the edge finder was bent toward the X+
side by +.001, so therefore the X- side would be bent away by -.001.
Now when you touched the X+ side, (recorded your reading) then turned
the edge finder 180 degrees and touched it again you'd have
theoretically have a .002 difference. So half that difference would be
roughly the center of the runout and spindle. Now the Y+ side of the
edge finder could be +.005 and the Y- side could be -.005, BUT they
don't necessarily influence the amount of runout in the X+ and X- sides.
Was that clear as mud, or did it help?

One thing that "could" influence the measurement of runout would be
the the angle of the stem. If the very tip was touched on one side,
and the other side was touched further up the stem due to being bent
over... then the true runout would be skewed. Is this type of
situation the ball tip electric edge finders would nullify any "bent
tip" inaccuracies.

--
BottleBob
http://home.earthlink.net/~bottlbob