Air Gaging Basics

Air Gage Basics
• Objectives of below article:
– To provide an understanding of air gage theory
– To learn some of the applications for air gaging
– To understand basic troubleshooting, maintenance and verification procedures

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Air Gaging Basics

Air gage theory is based on the principle that when a stream of air is passed through a small opening and “hits” another object, there will be a specific amount of back-pressure.  This back pressure is a highly accurate measuring tool
when used with an air comparator (air gage readout).The amount of back-pressure indicates the part size to the air comparator.

Air gage instruments have been designed, in their most widely used applications, to obtain highly accurate quantitative measurements of internal and external diameters of parts or workpieces.  Air spindles and probes are gages that are inserted into a workpiece to obtain the internal diameter of a part. Air rings and air snap gages fit over the outside of a part, thereby giving an external measurement of diameter.   The gage application generally indicates whether it will be a hand-held item or set up as part of an overall, stationary work station.

Generally, every gage will need a master to set/calibrate the gaging member and the air gage readout. This ensures dimensional data is both precise and quanitative. Masters are generally plugs, discs, rings, or set probes.
Master plugs and discs are used to calibrate air rings, snap gages, and other external measurement instruments. Master rings and set probes are used to calibrate spindles, air probes, and other internal measurement instruments. By
simplest definition, a master is used to dictate how much back-pressure indicates the internal or external measurement is closest to “the perfect dimension”.

An air gage is designed to check a specific dimension of a part/workpiece. Because the gages are made for several different parts in many different industries, the gages themselves will be unique.

The size, shape, number of nozzles, and column fittings will vary from gage to gage. Their style will be dictated by their intended use