It is apparent that, even with the rapid development of recent years, surprisingly little has been done by the makers to combat the most basic threats to component accuracy inherent in every machine tool. These are geometric alignment errors and thermal distortion of the machine structure.

Senior applications engineer to the CPT, Allan Kennedy said: "I've seen the most skilled engineers spend weeks trying to achieve this level of precision and then the machine might literally change with the weather! Not so with Volumetric Compensation Software (VCS) adjusting things automatically in response to the temperatures measured at critical points. This is certainly the way forward for machine tool makers to meet the ever rising standards demanded by hi-tech industry."

First the performance criteria of the selected machines was measured and catalogued in minute detail. There then followed a complete mechanical and electrical refurbishment including an upgrade to the Osai series10, a controller capable of running VCS without the need for additional hardware.

There then took place a second examination by the metrology experts of the CPT, this time to determine the calibration data that was to be stored for use by VCS.

Finally, the fully corrected machines were subjected to a series of exhaustive trials with remarkable results. Volumetric error was typically reduced from 78 to 16 microns, an improved accuracy of 80%. Consequently cycle times fell by 15% and the proportion of scrap components by 30%. In subsequent production trials it was found that the machines can be run faster and for longer periods of time without losing accuracy. All-night unattended runs are now a reality and measurement cycles are executed at three times the speed previously possible.

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