Ballbar testing explained

The 'standard' test calls for the machine tool to perform two consecutive circles; one in a clockwise direction, the other counter-clockwise. In practice there is an extra arc added before and after the test circle to allow for the machine speeding up and slowing down.

With the use of extension bars the test radius can be selected to reflect the size of the machine and the sensitivity to particular issues (e.g. large radius circles are better at highlighting machine geometry errors, smaller circles are more sensitive to servo mismatch or lag).

Real-time data capture helps to detect errors or problems as the test progresses. The test can be stopped to avoid wasting time which is important if you are carrying out a large radius test with a slow feed rate.

Before the launch of QC20 ballbar, testing in planes perpendicular to the standard X-Y test plane meant using special test mounts and repositioning of the centre mount. Now you can carry out tests covering three orthogonal planes without moving the centre pivot.

The secret to this is the ability of the QC20 ballbar system to carry out a restricted arc (220°) in two of the planes. This produces a modified test analysis for that arc but still produces an overall circularity value for that test.

With all three tests carried out around a single point it allows the use of the volumetric diagnostics report in Ballbar 20 software. This gives more information and is quicker than with previous systems.

A selection of report formats are available to International standards (e.g. ISO, ASME). The comprehensive Renishaw diagnostics (with volumetric analysis) include a series of different screens views and links to the help manual.

These reports give a value for a single overall indicator of machine positioning performance, e.g. circular deviation.

The reports can be customised and deliver an in-depth diagnosis of machine errors; all from a single test.