feeler gauge, practice with it on openings of known
is often underrated in its usefulness to the machinist.
Whenever possible, the design of most parts includes
a radius located at the shoulder formed when a change
is made in the diameter. This gives the part an added
margin of strength at that particular place. When a
square shoulder is machined in a place where a radius
should have been, the possibility that the part will fail
angle of 29° (14 1/2° to each side), and this is the
by bending or cracking is increased. The blades of
angle made into the gauge. The width of the flat on
most radius gauges have both concave (inside curve)
the point of the tool varies according to the number of
and convex (outside curve) radii in the common sizes.
threads per inch. The gauge provides different slots
for you to use as a guide when you grind the tool. It's
easy to set up the tool in the lathe. First, make sure
that the tool is centered on the work as far as height is
Nongraduated gauges are used primarily as
concerned. Then, with the gauge edge laid parallel to
standards, or to determine the accuracy of form or
the centerline of the work, adjust the side of your tool
shape. They include the straightedge, machinist square,
until it fits the angle on the gauge very closely.
sine bar, parallel blocks, gauge blocks, ring and plug
gauges, and thread-measuring wires. We'll explain the
CENTER GAUGE.--Use the center gauge
use of these gauges in the following paragraphs.
STRAIGHTEDGES. --Straightedges look very
the point of the gauge has an included angle of 60°. Use
much like rules, except they are not graduated. They
the gauge primarily to check and to set the angle of the
are used primarily to check surfaces for straightness;
V-sharp and other 60° standard threading tools. You
however, they can also be used as guides to help draw
or scribe straight lines. Two types of straightedges are
graduated into 1/4, 1/24, 1/32, and 1/64 inch for ease in
determining the pitch of threads on screws.
made of steel that is hardened on the edges to prevent
FEELER GAUGE.--Use a feeler (thickness)
wear; it is the one you will probably use most often.
The straightedge shown in view B has a knife edge
closely mating surfaces. When you USC a combination
and is used for work requiring extreme accuracy.
of blades to get a desired gauge thickness, try to place
the thinner blades between the heavier ones to protect
the thinner blades and to prevent their kinking. Do
not force blades into openings that are too small; the
blades may bend and kink. To get the feel of using a
Figure 1-21.--Feeler (thickness) gauge.