Air Gages for Internal Diameters
Air plug gages which are also referred to as an air probe, air spindle or mandrel are gages that are inserted into a work piece to obtain the internal diameter of a part. They are made of a precision ground hardened steel body incorporating two or more air gage nozzles. Air is passed through the probe body to the nozzles where a backpressure is produced by the surface of the workpiece. An air gage readout (air comparator) senses the resulting backpressure and displays the size of the workpiece. In the picture , the nozzle tips are recessed a small amount below the body of the probe. This feature makes the air gage measurement essentially non-contact; consequently, wear does not directly affect the accuracy of the gage measurement. In addition, the flow of air purges the gaging surface of contaminants making the measurements highly repeatable. By using an opposed set of nozzles, the measurement is made independent of how the operator positions the probe radially within the test bore. This "differential" type of measurement makes it possible to obtain extremely accurate measurements with limited operator skill. Air probe styles vary depending on how close the air jets are to the leading edge of the probe body. "Thru-hole" style probes have gaging nozzles located near the center of the probe body. "Blind" or "Super-blind" probe styles have nozzles located near the leading edge. Master ring gages are used to set air probes, bore gages and other internal measurement instruments. Master plug gages and master setting discs are used to calibrate air rings, snap gages, and other external measurement instruments.
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