CNC machine ballbar - video

CNC machine ballbar. By Bryan Howard. 35:34 video:

https://www.youtube.com/watch?v=xbM0I1bafhM

I watched most of the video and still don’t understand the instrument’s purpose. A 30 second overview sure would have helped.

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Originally Posted by rgsparber

I watched most of the video and still don’t understand the instrument’s purpose. A 30 second overview sure would have helped.

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I looked up ballbar tester and while it was mildly (maybe that is way too strong a word) interesting, perhaps if I had anything with anywhere close to the resolution...

At any rate, here is a site with a video that actually explains how the testing works and the video is less than 1/16 the time commitment...

https://www.renishaw.com/en/ballbar-...xplained--6818

Thanks! Very helpful.

Rick, I didn't watch the whole thing yet but a ballbar is used to qualify a CNC machine. If you are machining a circle, put the center at the origin of the x and y axis. So you will have a + and - value along each axis. The circle is composed of 4 quadrants. An axis motor reverses rotation at the start of each quadrant. Eg. if starting at 12 o'clock the cutter is moving +x and -y at the same time. At 3 o'clock x reverses and you are now moving -x, -y at the same time. This reversal of axis rotation can be seen as tool marks, or even non-circularity if there are kinematic problems. The ball bar test clearly shows the non-orthogonality (or backlash) of the machine. If you look at his coupling you can see its reversal when reaching the 9 o'clock position.

The ball bar test was invented and patented by Jim Bryan at the Lawrence Livermore National Lab in the early 80's, not by Renishaw as everyone assumes.

Thanks for the education.