Modern Machine Shop

OCT 2018

Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.

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Page 98 of 147

MODERN MACHINE SHOP 97 BETTER PRODUCTION Optical Micrometers errors, Timken has found the gage type to be capable of meeting the company's accuracy specifications. Technically, diameter measurements can be obtained on a part located physically at multiple locations in the measurement region. However, the part axis has to be consistently located at a specified location in the measuring region in order to take advantage of the mapping, and this is how the micrometer delivers its most accurate results. In addition, the part axis must be opti- cally aligned to the micrometer; that is, the part axis must be orthogonal to the direction of the micrometer scan. Misalignment in the direction of scan will not generally result in a significant error in the measured diameter at that cross sec- tion. However, for some part geometries (tapers or curvatures along the part's length) and large skews, the measured diameter will not corre- spond to the true diameter of the part at that plane. Misalignment perpendicular to the direc- tion of the scan will more likely result in an error of the measured diameter at that cross section. Mr. Keller explains how new users are trained to understand the new technology's sensitivities in this area. In an exercise, a new user is asked to locate a 10-mm-diameter master part at multiple locations in the measuring region of an optical micrometer with 30-mm measuring range, he says. The distribution of measured diameters is recorded, and the distribution mean is compared to the true diameter. Then, that new user will measure the master part multiple times again using workholding registration that is integrated into the gage, which causes the part axis to be located at a specific desired location. In the latter case the distribution is much narrower and the distribution mean is much closer to the true mean. After this demonstration, workers who are new to the optical micrometer understand the importance of diligence and consistency in part axis location, he says. The greatest concern Mr. Keller's department had upon deployment of the micrometer has been part cleanliness. "Part cleanliness require- ments for optical inspection are similar to the requirements for tactile inspection with a CMM. Because of smaller gaging forces, CMMs tolerate less contamination on the part surface than do comparative contact gaging," he says. Optical micrometers, similarly, cannot tolerate any sur- face contamination at the measurement plane. As a result, Timken is deploying part cleaning ahead of optical measurement, much as it has IN PARTNERSHIP WITH: Search Machines Smarter. Machining Center Drill/Tap Boring Mill Milling Machine Machine Type: The Machine Tool Search Engine

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