Re: [CAD_CAM_EDM_DRO] Measuring accuracy

Gregory Kamysz wrote:

>What kind of test does one run on a mill to define it's accuracy? Is
>there a standard code or method used to do this? Or do I just run some
>parts and see if I've made scrap or something useful?
>
>
>

Probably the most common standard is the "ball - bar" test. A device
made by Renishaw, called a ball-bar tester, is attached to the spindle and
table. It has a shaft encoder on the table-mounted part, a ball that
fits in the spindle, and a bar with a very sensitive length measuring
encoder that goes between the two. You program a circular motion
with a radius matching the length of the bar. The shaft encoder
records progress around the circle, and the bar encoder measures
errors in the radius at each instant. A drawing with exaggerated
errors is produced. An elliptical trace indicated orthogonality
error. Jumps at each axis reversal indicates low servo gain or
backlash. Jiggles in the trace indicate problems in the screws,
servos, ways and similar components. Egg-shaped traces indicate
short-term errors in the screws.

Jon