the angles that have to be ground on a high-speed
single-point cutting tool in the following paragraphs.
which the end surface of the tool is ground so that the
front face edge of the tool leads the front surface.
Side rake is the angle at which the top surface of
Angle Of Keenness
the tool bit is ground away making a slope either away
view A, shows a positive side rake angle. When the
view A) is formed by the side rake and the side relief
side rake is ground toward the side cutting edge, the
ground in a tool. The angle of keenness is equal to
side rake has a negative angle. The amount of side
90° minus the sum of the side rake and side relief
rake influences to some extent the size of the angle of
angles. Generally this angle is smaller for cutting soft
keenness. It causes the chip to "flow" to the side of
the tool away from the side cutting edge. A positive
side rake is most often used on ground single-point
Side Cutting Edge
tools. Generally, the side rake angle will be steeper
(in the positive direction) to cut the softer metals and
will decrease as the hardness of the metal increases.
ground on the side of the tool that is fed into the-work.
A steep side rake angle in the positive direction causes
This angle can vary from 0° for cutting to a shoulder,
the chip produced in cutting to be long and stringy.
up to 30° for straight turning. An angle of 15° is
Decreasing the angle will cause the chip to curl up and
recommended for most rough turning operations. In
break more quickly. A negative side rake is
turning long slender shafts, a side cutting edge angle
recommended when the tool will be subjected to
that is too large can cause chatter. Since the pressure
shock, such as an interrupted cut or when the metal
on the cutting edge and the heat generated by the
being cut is extremely hard.
cutting action decrease as the side cutting edge angle
increases, the angle should be as large as the
machining operation will allow.
End Cutting Edge
The back rake is the angle at which the top surface
of the tool is ground away mainly to guide the
direction of the flowing chips. It is ground primarily
ground on the end of the tool to permit the nose to
to cause the chip to "flow" back toward the shank of
make contact with the work without the tool dragging
the tool. Back rake may be positive or negative. It's
the surface. An angle of from 8° to 30° is commonly
used, with approximately 15° recommended for rough
from the nose toward the shank, and it's negative if a
turning operations. Finish operations can be made
reverse angle is ground. The rake angles help form
with the end cutting edge angle slightly larger. Too
the angle of keenness and direct the chip flow away
large an end cutting edge angle will reduce the
from the point of cutting. The same general recom-
support given the nose of the tool and could cause
mendations concerning positive or negative side rake
premature failure of the cutting edge.
angles apply to the back rake angle.
the tool, helps to carry away the heat generated by the
which the side of the tool is ground to prevent the tool
cutting action, and helps to obtain a good finish. A
bit from rubbing into the work. The side relief angle,
tool whose nose is ground to a straight point will fail
like the side rake angle, influences the angle of
much more rapidly than one with a slight radius or
keenness. A tool with proper side relief causes the
rounded end ground or honed on it. However, too
side thrust to be concentrated on the cutting edge
large a radius will cause chatter because of excessive
rather than rub on the flank of the tool.
tool contact with the work. Normally, you should use