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Gages Classes

In mass-manufacturing operations it is often uneconiomical to attempt to obtain absolute sizes during each inspection operation. In many cases , it is only necessary to determine whether one or more dimensions of a mass-produced part are within specified limits. For this purpose, a variety of inspection instruments referred to as gages are employed. However , the distinction between gaging and measuring devices is not always clear as there are some instruments referred to as gages that do give definite measurements.
To promote consistency in manufacturing and inspection, gages may be classified as working , in section , and reference or master gages. Working gages are used by the machine operator or shop inspector to check the dimensions of parts as they are being produced . They usually have limits based on the piece being inspected. Inspection gages are used by personnel to inspect purchased parts when received or manufactured parts when finished. These gages are designed and made so as not to reject any product previously accepted by a properly designed and functioning working gage. Reference or master gages are used only for checking the size or condition of other gages , and represent as exactly as possible the physical dimensions of the product.
A gage may have a single size and be referred to as a nonlimit gage, or it may have two sizes and be referred to as a limit gage. A limit gage, often called a “go?and “not go?gage, establishes the high and low limits prescribed by the tolerance on a dimension. A limit gage may be either double-end or progressive . A double-end gage has the “go?member at one end and the ?not go?member at the other. Each end of the gage is applied to the workpiece to determine its acceptability. The “go?member must pass into or over an acceptable piece, but the “not go?member should not. A progressive gage has both the “go?and “not go?members at the same end so that a part may be gaged with one movement.
Some gages are fixed in size while others are adjustable over certain size range. Fixed gages are usually less expensive initially, but they have the disadvantage f not permitting adjustment to compensate for wear.
Most gages are subjected to considerable abrasion during their application and must therefore be made of materials resistant to wear. High-carbon and alloy steels have been used as gage materials for many years because of their relatively high hardenability and abrasion resistance. Further increased surface hardness and abrasion resistance may be obtained from theh use of chrome plating or cemented carbides as surface material on gages . some gages are made entirely of cemented carbides or they have cemented carbide inserts at certain wear points . Chrome plating is also used as a means of rebuilding and salvaging worn gages.