Modern Machine Shop

SEP 2018

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MMS SEPTEMBER 2018 34 mmsonline.com QUALITY GAGING TIPS Measurement Tools AUTHOR | George Schuetz Director of Precision Gages, Mahr Inc. because these contacts have such a broad measur- ing surface, parallelism errors can creep into the measurement. Therefore, it is important to check the parallelism of the contacts using a precision ball on many locations between the contact faces. However, one problem with using micrometers is that measurements are subject to variation between operators. The micrometer is a contact instrument. Sufficient torque must be applied to the micrometer to make solid, positive contact between the part and the instrument. However, the only torque calibration in the human hand is the operator's "feel." What feels like solid contact to one operator may not feel correct to another, so the readings will be different. In order to eliminate the "feel" part of the measurement, the designers of micrometers incorporated a ratchet or friction thimble mechanism to ensure more consistent contact pressure. Digital micrometers also reduce subjectiv- ity. Before, reading a micrometer thimble was always an area of difficulty for both beginners and experienced users. Switching from inches to metrics, or simply misreading a line, could mean the difference between a good or bad part. Dig- ital micrometers eliminate this problem with their direct reading of the part size and their ability to convert from inches to millimeters. New versions offer the ability to classify the part as good or bad, and to collect the measured results with a data cable or send them wirelessly to a data documentation system. The latest advancement is the addition of the rapid speed drive to the rotating thimble. Some versions of the sliding spindle micrometer employ a rapid drive that allows for moving the spindle 10 times faster than a standard spindle. Most micrometers have a thread pitch of 0.5 mm per full rotation of the spindle, but versions are now available with a 5.0-mm-per-revolution move- ment. This is especially beneficial when measur- ing multiple diameters. With a sliding spindle, the non-rotating system can measure film thick- ness without twisting and damaging the materials during measurement. We will hold our breath to see what is next for this shop-worthy tool. BOOTH# 432013 60º, 90º, and 120º included angles THREAD MILLS SINGLE POINT PORT TOOLS CAVITY TOOLS SPECIALTY INDEXABLE BORING A Global Name in Cutting Tools www.sct-usa.com sales@sct-usa.com 1.805.584.9495 1.800.383.2244 HIGH PERFORMANCE New Helical Chamfer Mills Scientific Cutting Tools

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