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66 Part II: Metrology
• Slide the surfaces of the blocks together as shown. Apply pressure
while sliding the blocks. The blocks should adhere to each other
strongly after being rotated into place.
Other Attribute Gages
Part II.A.2
In some operations it is uneconomical 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 gauging and measuring devices
is not always clear as there are some instruments referred to as gages that do not
give definite measurements.
To promote consistency in manufacturing and inspection, gages may be classified
as working, inspection, 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
manufactured 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/
no-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 “no-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 no-go member should
not. A progressive gage has both the go and no-go members at the same end so that
a part may be gauged with one movement.
Some gages are fixed in size while others are adjustable over certain size
ranges. Fixed gages are usually less expensive initially, but they have the disadvantage
of not permitting adjustment to compensate for wear.
Most gages are subjected to considerable abrasion during their application
and therefore must 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 through the 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.