CNC machine ballbar - video

[Saltfever]

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.