Quality Magazine - April 2009 - (Page 30) | QUA LIT Y M EA SU REM E N T | MEASUREMENT MADE SIMPLE Shaft measuring systems can accomplish checks faster than other methods and have the ability to perform directly on the shop floor. BY PAT RI CK NUGE N T AND DEWE Y C H R I STY SHAFT S hafts are everywhere. Whenever a part is made to turn on an axis, a shaft is usually involved. Shafts can be tiny enough to turn the gears in a watch or large enough to spin the propellers of huge ships, and they can contain any number of functional features, such as gears, splines, threads, tapers, grooves and bearing surfaces—all of which have associated critical dimensions. It is not unusual, for example, for a single, modest-sized shaft for an automotive transmission, to require more than 60 dimensional checks during its manufacture. Dimensional checks on shafts and shaft features are done with every type of gage imaginable, from basic handheld devices, such as micrometers and snap gages, to high-end coordinate measuring machines (CMMs). However, there is growing popularity for a loosely defined class of shaft measuring systems that can accomplish these checks faster than other methods, and do so directly on the shop f loor where the shafts are made. Frequently used in Europe, shaft measuring systems are gaining U.S. popularity in a number of highvolume applications. Shaft measuring systems are a good solution for shafts that meet fairly broad criteria. The first criterion is tolerance range. Shaft measuring systems are designed to work almost exclusively with turned parts. With internal machine accuracies in the 1 micron range, or 50 millionths of an inch, today’s shaft measuring systems are best used with parts having tolerances of approximately 10 times that, or about 5∕10 of an inch. That is pretty much the tightest tolerance for turned parts, but loosest for ground diameters. Therefore, ground shafts are better measured by other means—usually in a metrology lab. Different manufacturers offer a variety of systems able to measure different ranges of parts, but the general spread is shafts as small as 25 millimeters, or 1 inch, in length up to 1,000 millimeters, or 40 inches, in Optical shaft measuring systems, such as matrix array systems, can be successful for transmission shaft applications. A number of checks can be performed, including diameter across the shaft, angle of tapers, depth of grooves and run-out of a shoulder to the overall axis of the shaft. Source: Mahr Federal Inc. TECH TIPS Compared with handheld gages, dedicated shaft measuring systems offer greater efficiency in that they can make a number of checks with a single setup and a single scan. Line scan technology is very fast. An image of the part dimensions is created by means of a series of lines. The higher resolution of matrix array shaft measuring systems makes measurements more stable and accurate, and allows measurement of much smaller features than the calculated image of a line scan. 30 QUALITY | April 2009 www.qualitymag.com http://www.qualitymag.com
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