Metrology Fixtures and CMM Fixtures

Metrology fixtures and CMM fixtures are used to hold and position parts, probes, or workpieces during dimensional gaging and other measurement operations. Metrology, the science of measurement, entails both practical and theoretical considerations. Coordinate machine measurement (CMM) involves measuring an object’s physical geometry. In addition to CMM, common metrological processes include dimensional gaging, form measurement, reverse engineering, image capture, surface roughness measurement, and profilometry. For each type of process, metrology fixtures and CMM fixtures should hold the part, probe, or workpiece steadily enough to avoid movement and vibration. Materials of construction for these fixtures include aluminum, steel, ceramic, plastic, and glass.

There are many types of metrology fixtures and CMM fixtures. Examples include gaging fixtures (gage fixtures, gauging fixtures), form gaging fixtures, and measurement fixtures. Gaging fixtures are measuring stations that are customized for specific parts. For example, gage fixtures and gauging fixtures for automotive applications are used to check the holes in engine blocks, gear cases, and valve heads. Form gaging fixtures are another type of device. These metrology fixtures and CMM fixtures are used during inspections for roundness, angularity, squareness, flatness, runout, taper, and concentricity. There are two basic types of form gages: contact and non-contact. Contact instruments measure surface texture by dragging a sharp, pointed tool across the surface. Non-contact products measure surface texture by optically scanning a surface with a light or laser.

Metrology fixtures and CMM fixtures include profilometry fixtures, QA fixtures, shop gaging fixtures, and OQ room fixtures. Profilometry fixtures are used with profilometers, instruments that are used to measure a surface’s profile in order to quantify its roughness. Quality assurance via checking fixtures (QA fixtures, Q.A.-Fixtures) measure parts with dedicated check fixtures and hand-held data collection devices. The check fixtures range from simple to complex. The data collectors are shop-hardened, hand-held computers that sound an audible warming if a part is out of tolerance. Shop gaging fixtures are used with shop floor gaging systems such as those used in the automotive industry. Metrology fixtures and CMM fixtures also include OQ room fixtures, products that are designed for use in clean rooms, laboratory instruments and equipment.

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