to Kirkwood. Measuring pitch diameter is particularly tricky since it is the diameter of an imaginary cylinder where the thread is as thick as the groove.
Perhaps the ultimate device is a contour tracer, or
contracer, that creates a trace of the profi le of the thread, creating a 2D trace over a defi ned distance. One example is the Mitutoyo Contracer CV-2100 which provides measur- ing resolutions of up to 2.5 microns. “This provides data now that can be interrogated for angles, radii, or pitch—all
A number of important parameters, not all shown here, are needed for accurate measurement of screw threads.
specifi c and variable qualities of a thread profi le,” said Kirk- wood. This would allow a much deeper analysis of critical threads. In his 30 years of professional experience, Kirk- wood has worked mostly in energy extraction, and he has seen a profound change since 2010. “Since the 2010 Gulf Oil Spill, customers like Shell and Chevron, are demanding more traceability with higher quality metrology,” according to Kirkwood.
Automotive Quality and Speed At the high end of the metrology spectrum is using an optical comparator or a general-purpose CMM, such as a Zeiss Micura equipped with a VAST-XT-Gold sensor for thread measuring. There are times when a CMM is called for, according to David Wick, manager for product management for Zeiss Industrial Metrology (Maple Grove, MN). “In general, measuring threads and taps is important to industries such as automotive or aerospace, where our customers manu- facture a cast part with fl at machined surfaces that contain tapped bolt holes in it,” said Wick. “Think of a water pump for your car—it’s cast, has fl at surfaces where the gaskets go, and tapped bolt holes. Ensuring the tapped holes are the
April 2016 |
AdvancedManufacturing.org 71 See us at MFG4 Booth #1520
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