TM 9-3418-200-14 & P
right angles to the cutting edge. When measured in a plane perpendicular to the cutting edge at the end of the tool, It is
called the end lip angle. When measured at the end of chip flow, it is called the true lip angle.
BACK-RAKE ANGLE --The back-rake angle is the angle between the face of a tool and a line parallel to the base of the
shank.
END-RELIEF ANGLE --The end-relief angle is the angle between the portion of the end flank immediately below the
cutting edge and a line drawn through that cutting edge perpendicular to the base.
SIDE-RAKE ANGLE --The side-rake angle is the angle between the face of a tool and a line parallel to the base.
TRUE-RAKE ANGLE --The true-rake angle, under actual cutting conditions, is the actual slope of the tool face toward the
base from the active cutting edge in the direction of chip flow. This, angle varies with the setting of the tool and with the
feed and depth of cut.
RIGHT-CUT TOOL --A right-cut single-point tool when viewed from the face, has the cutting edge on the right side
(fig. 10).
LEFT-CUT TOOL --A left-cut tool has the cutting edge on the left when looking at the false (fig. 9).
A bent tool has the point bent to the right or left to make its operation more convenient, see figures 11 and 12.
SHAPE OR FORM
The shape of the tool may be curved, flat, or its sides may converge to a sharp point. The shape or form of the tool will
depend upon the surface being machined. For example, a tool with a curved form could not be used to produce a
rectangular slot or a sharp corner. Neither would a tool with a sharp corner be recommended for a curved surface or for
roughing a flat surface. See figures 15 through 20.
There is usually a difference between the roughing and the finishing tool. In addition, a tool may be offset, or bent to the
right or to the left, and may feed either in a right-hand or left-hand direction, see figures 9 through 14.
A tool with a rounded nose may be used to rough out both steel and cast-iron surfaces, and with slight modification may be
used to produce a finish cut.
A shear-cut tool is usually preferred for finishing steel (fig. 14) whereas, a tool with a flat end shaped as shown in figure 13
is extensively used to finish cast-iron.
ACCURATE MEASUREMENTS
Careful and accurate measurements are essential to good machine work. The ability to take accurate measurements can
only be acquired by practice and experience. All measurements should be made with an accurately graduated steel scale
or a micrometer. Never use a cheap steel scale, or a wood ruler, as they are likely to be inaccurate and cause spoiled
work.
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