Machine-Geometry

A ballbar test checks the machine geometric accuracy by measuring circular interpolation errors. The test uses a precision ballbar mounted between the spindle and the machine table. The machine runs a circular program and the ballbar measures the deviation from a perfect circle down to micron resolution. In my experience, the ballbar is the single most useful diagnostic tool for verifying machine geometry before running deep hole jobs that demand straightness tolerances under 0.01 mm per 100 mm of depth. ...

A laser interferometer measures machine positioning accuracy with sub-micron resolution. I use one for annual calibration of production deep hole drilling machines. The first time I ran a full laser calibration on a machine that was supposedly within spec, I found positioning errors of 0.08 mm per meter — four times the acceptable limit. The compensation corrected those errors and improved the hole position repeatability from 0.05 mm to 0.01 mm. ...