Motion System Design

Dimensional inspection, decades later

The precision gear inspection lab described in the July 1959 issue of Motion System Design no longer exists at Pratt & Whitney Rocketdyne, headquartered in East Hartford, Conn. Today, in an area officially known as the Precision Measurement Room, in Northridge, Calif., inspection takes place on everything from small turbine blades to large turbine exhaust housings. There, a coordinate measurement machine or CMM is primarily used to perform dimensional analysis. With an accuracy of 0.000060 in., the CMM is a much more powerful machine than its early manual measurement predecessors. Using CAD/CAM model-based inspection, the CMM yields significantly greater accuracy in approximately 10% of the time required by the antiquated technology methods mentioned in our 1959 news article.

Richard Burley, a 43-year veteran of Pratt & Whitney Rocketdyne, has been working in dimensional analysis since his early days as a tool designer. He has personally witnessed the evolution of dimensional inspection. Early on, granite surface plates and optical comparators were used. Today, these relics sit collecting dust, and are often replaced by CMMs and laser trackers. Like the CMM, the laser tracker has far surpassed previous dimensional inspection techniques.

“State of the art technology like the laser tracker provides large volume, mobile inspection capabilities,” explains Burley. “Instead of moving large parts in and out of the room, we travel to the parts.”

This month's history lesson courtesy of Melissa Beck, Precision Measurement Room staff, Pratt & Whitney Rocketdyne. For more information, visit

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