testing for squareness

Hi,

Without wasting bandwidth, I'll like to post these question to the
list:

How does one test and compare CNC machines, particularly CNC mills?

How does one measure repeatibility, precision, orthogonality
(squareness)?

I was told one way to test for squareness is to machine a circle. If
the x and y axes are not 90 degrees to each other, the circle will
not be a perfect square. Has anyone ever done a test like this, or
any other tests? How does one measure the deviation from squareness?

For the z-axis, tramming? was described in some earlier posts. Can
this be used as a measure of the orthoganality of the z-axis to the
xy plane, perhaps a figure expressed as deviation from horizontal per
inch or per meter?

| |
| | collet
\ | /
\ /
| wire bent into Z shape and rotated
|_______
tip |
touching | tip distance d above surface
.................... flat surface

measure of deviation = d/2L where L is the length of the knee?????


Thanking you in advance.

Peter

Great List!!!!!!