In article ,
Karl Townsend wrote:


Bonus Algebra question:

I wanted two estimates of hole diameter. In the above routine, first
you can get X center and a chord length. After moving to Xcenter, you
get Y center and a diameter and now know how far off center the above
chord it. So, for a given chord length and distance from center: what
is the dimaeter of the circle? Note, the data I have is the four touch
points on the hole.

This would be helpful to know on worn parts.


Second note. I said algebra, not trig, for a reason. I can draw a
picture and solve the problem for a given set of data. What I need is
the general case, given four X values and four Y values: what formula
can I enter into the computer to give the answer? At least for me,
this is MUCH harder to do.

There is a complication: holes need not be round, even new holes, but
especially if worn.

How should wallowed out or rounded triangular holes be handled?
Smallest diameter, largest diameter, the average, something else?

Non-circular holes need not be symmetric, so the location of the center
may vary as well. Here, the best approach is usually some kind of
average.

Given that measurements are made by machine, is there any reason to be
limited to four measurements? With more measurements, it becomes easier
to detect and handle irregular holes.


Joe Gwinn