On 06/16/2011 12:23 AM, Ignoramus16551 wrote:

Jon, I wonder if a circle, milled on a moving table, represents a true
reference surface, or not. I used the top of the Kurt vise as a
reference surface.

Well, if the ways have wear, this is the only way to establish the true
"plane" of motion. Of course, it isn't actually a plane, but a surface
that is close to a plane.
It was not "really hard", like changing a transmission on a car on a
hot day, but after a while I hit a virtual wall and could not improve
beyond 0.001" over 4 inches swing.
If the object you are tramming to is truly planar, you should be able to
do better. But, if it is rocking on burrs on the table or not truly
flat, then it will be impossible to tram to it with any greater accuracy
than the flatness of it.

I can't get better than .001", maybe even worse, but when sweeping the
circle, then the deviation of the ways becomes quite clear. I set it so
that the +X and -X are equal, and the +Y and -Y are equal. But, there
are significant swings of the indicator, for instance from +X around to
-X, there is a rise in the middle, because the table moves in a slight
arc from one end to the other.

it won't get any better until I tear the machine down and scrape the ways.

Jon