CHESTER Craftsman, Instruction Manual

Page: 14 / 53

Tool Angles
There are three important angles in the construction of a cutting tool rake angle, clearance angle and
plan approach angle.
Figure 5. Main Features of a Single Point Cutting Tool
Rake Angle
Rake angle is the angle between the top face of the tool and the normal to the work surface at the cutting
edge. In general, the larger the rake angle, the smaller the cutting force on the tool, since for a given
depth of cut the shear plane AB, shown in Figure 4 decreases as rake angle increases. A large rake
angle will improve cutting action, but would lead to early tool failure, since the tool wedge angle is
relatively weak. A compromise must therefore be made between adequate strength and good cutting
action
.
Metal Being Cut
Cast Iron
Hard Steel /
Brass
Medium
Carbon Steel
Mild Steel Aluminium
Top Rake Angle
0° 8° 14° 20° 40°
Table 1. Typical value for top rake angle
Clearance Angle
Clearance angle is the angle between the flank or front face of the tool and a tangent to the work surface
originating at the cutting edge. All cutting tools must have clearance to allow cutting to take place.
Clearance should be kept to a minimum, as excessive clearance angle will not improve cutting efficiency
and will merely weaken the tool. Typical value for front clearance angle is 6° in external turning.
Chester UK Craftsman Lathe
13