Mechanics of Metal Cutting
(Practical Applications of Tool Design)
1
The Mechanics of Metal Cutting is controlled by
three main elements.
•Rake Angles
•Lead Angles
•Clearance Angles
2
Rake Angles
3
Side rake
Single point tool geometry
γ
f
Primary motion
of the job
Side Clearance
Feed motion
α Section F-F
f
P
F F
End α k k !r
p r
clearance
ψ
γp Back rake Lead
angle
Section P-P
4
Basic Cutting Tool Geometry-Turning
SCEA
Side Cutting Edge Angle
Back Rake
Side Rake
5
Rake Angles Control Edge
Strength
FORCE
POSITIVE
•TRS measures the bending
fracture strength of carbides
6
Rake Angles Control Edge Strength
R C E
FO
NEGATIVE
SUPPORTED:
•Measure of deformation More Compressive
Loading
resistance
7
Rake Angles - Basic Milling Geometry
8
POSITIVE AXIAL RAKE POSITIVE RADIAL RAKE
9
NEGATIVE AXIAL RAKE NEGATIVE RADIAL RAKE
10
POSITIVE AXIAL RAKE NEGATIVE RADIAL RAKE
11
Rake Angles Control
Edge Strength
Radial Rake has a Radial Rake
major impact on (+) (-)
cutting edge strength
Radial Rake absorbs
the interrupted cut
Axial Rake
12
Cutting Forces
Ft = Tangential Force
Ff = Feed Force
Ft Fr = Radial Force
Ff
Fr
13
Rake Angles control
Cutting Forces
-5
NEGATIVE
Cutting Forces
change
approximately
+6 1% per degree
of Rake change
(mild steel)
POSITIVE
14
Rake Angles control
Cutting Forces
Radial Rake
(+) (-)
Axial Rake has a
major impact on
cutting forces.
15
Rake Angles control
Cutting Forces
Both axial and radial Radial Rake
(+) (-)
rake have comparable
effects on cutting
forces.
16
Rake Angles Control
Cutting Forces
Negative Positive
Radial Rake Radial Rake
Designed for a specified clearance under the
heel of the insert.
17
Top Topography is used to
Enhance Axial Rake
18
Chip Flow Characteristics
Rake angles control the direction of chip flow
(-) (-) (+)
(+) (+) (-)
Positive / Positive Negative / Negative Negative / Positive
(Shear-Clear)
19
Rake Angles:Drills
Radial Rake Axial Rake Angle (Helix)
20
Negative Positive
Axial Axial
Rake Rake
Spiral Point Spiral Flute
21
Rake Angles:Reamers
Axial Rake Angle
Neutral Axial Rake
Radial
rake Primary
Positive Axial Rake angle Clearance
Secondary
Clearance
Negative Axial Rake
22
Lead Angles
23
Lead Angle controls the
Direction of Cutting Forces
45 Lead
Angle
Axial
load
Table Feed
Radial
load
24
Direction of Cutting Forces
Direction of Cutting
Forces
25
Direction of Cutting Forces
Increasing the Lead
Angle places the forces
more into the Radial
Plane.
26
Lead Angles control
direction Cutting Forces
Forces
directed into
the spindle
Forces directed
across the
spindle
27
Lead Angles control
direction Cutting Forces
90° 118° 140°
The greater the angle, the greater the rigidity.
28
Clearance
Angles
29
Clearance Angles
90 Degree included
79 Degree included
Angle
Angle
5 degree Neg. Rake
5 degree
Positive. NEGATIVE
Rake
POSITIVE
6° Degrees 5° Degrees
Clearance Clearance
30
Back Clearance
31
Clearance Angles
Radial Rake
Arc of the cut
(+) (-)
Radial Rake is designed to
provide a specified amount
of clearance under the heel of
the insert
32
Clearance Angles
Lip Relief
Angle
Flank
Margins
Body Point
Angle
Clearance
Drill
(Radial) Diameter
33
Tap Margins
Concentric
Grind
(No Clearance)
34
Tap Margins
CONCENTRIC CON-ECCENTRIC ECCENTRIC
No Clearance Partial Clearance Clearance
35
36
