Tool Geometry of Single Point
Turning Tool (SPTT) in Metal Cutting
By
Dr. Kazi Sabiruddin
Assistant Professor
Mechanical Engineering Dept.
IIT Indore
Contents
• Why to learn tool geometry of SPTT?
a) Rake & Clearance angles
b) Reference systems to describe tool geometry
• Study of tool geometry
a) Tool-in-Hand system
b) Machine Reference System/American Standard’s Association (ASA)
c) Tool Reference System
i) Orthogonal Rake System (ORS)
ii) Normal Rake System (NRS)
• How to designate tool geometry?
a) ASA b) ORS c) NRS
Why to learn tool geometry of SPTT?
Material and Geometry of tool Guides (3 Es)
• Effective Machining (Reqd. shape, size, finish etc.)
• Efficient Machining (How fast?)
• Economic Machining (Low cost)
Tool Geometry affects
• Mechanism of chip formation
• Cutting temperature
• Wear
• Tool life
• Surface finish
Rake and Clearance angles
Vc = Cutting Velocity Vector
πR = Reference Plane
γ = Rake angle
α = Clearance angle
[Shaping]
Work Piece
πR ┴ Vc
[Turning]
How to Define γ and α?
Rake angle (γ):
Inclination of chip flowing surface (rake surface) of tool to
reference plane (πR) for
easy machining, less force requirement,
less temperature generation, less wear of tool surface
and good finish of work-piece surface.
Clearance angle (α)
Inclination of clearance surface of tool from the machined /
finished surface for
Prevention of rubbing
safety ( tool/job/machine/operator)
Sign of Rake & Clearance Angle
Positive Rake Zero Rake Negative Rake
• Less cutting force • Simple design • Thick tool (high β)
• Less power consumption • To manufacture • Strong tool
• Less temperature generation form tools • High cutting force
• Thin tool (low β) • High power consumption
• Weak tool
Clearance Angle (α): Always positive (3o - 15o)
Tool material
Work material
Type of machining (turning, milling, shaping etc.)
Tool-In-Hand System
N
Job
So
• Direction of machining (Right hand/Left hand) tool
• Identification of Planes (Rake, Flank etc.)
• Identification of Edges (Cutting Edges)
• Identification of Nose, Positive/Negative Rake
Measurement of angles, nose radius, etc. is not possible
Tool Geometry: Machine Reference System
(ASA)
(Cutting velocity vector)
(Cross feed direction)
(Longitudinal
Feed direction)
πR = Reference plane
πx = Machine Longitudinal plane II to feed direction & perpendicular to πR
πy = Machine Transverse plane II to cross feed direction & perpendicular to πR & πx
Studying Tool Angles in ASA
γx = Side Rake Angle/
Axial Rake angle
γy = Back Rake Angle
αx = Side Clearance Angle
αy = Back Clearance Angle
Φs = Approach Angle
Φe = End Cutting Edge Angle
r = Nose Radius (in inch)
r r = Deliberate curving of
Nose/Tool tip to:
• Strengthen Cutting Point
• Improve Surface Finish
Studying Auxiliary Back Clearance
Angle (αy’)
Ym
Ym
πx
Zm
αy’ Vc
πR
πy
Definition of Tool Angles in ASA
γx (Side Rake Angle)
Angle of inclination of rake surface from πR & measured on πx.
γy (Back Rake Angle)
Angle of inclination of rake surface from πR & measured on πy.
αx (Side Clearance Angle)
Angle of inclination of principal flank surface from Vc & measured on πx.
αy (Back Clearance Angle)
Angle of inclination of principal flank surface from Vc & measured on πy.
Φs (Approach Angle)
Angle of inclination of principal cutting edge from πy & measured on πR.
Φe (End Cutting Edge Angle)
Angle of inclination of principal cutting edge from πx & measured on πR.
Tool Signature in ASA:
γx , γy , αx , αy’, Φe , Φs , r (inch)
Tool Geometry: Tool Reference System
Orthogonal Rake Systems (ORS)/ISO old
Cutting Velocity
Orthogonal Cutting Axis
Axis
πR = Reference plane perpendicular to Vc
πo = Orthogonal plane; perpendicular to πR , πc & cutting edge
πc = Cutting plane; contains cutting edge & perpendicular to πR.
Studying Tool Angles in ORS
λ = Inclination Angle
γo = Orthogonal Rake Angle
αo = Orthogonal Clearance Angle
Ф = Principal Cutting Edge Angle
Tool Signature in ORS: Ф1= Auxiliary Cutting Edge Angle
λ, γo , αo , αo’ , Φ1 , Φ , r (mm)
r = Nose Radius (in mm)
Studying Auxiliary Orthogonal
Clearance Angle (αo’)
πo’ = Auxiliary Orthogonal Plane
πc’ = Auxiliary Cutting Plane
αo’ = Auxiliary Orthogonal Clearance Angle
Tool Geometry: Tool Reference System
Normal Rake Systems (NRS)/ISO New
NRS Co-ordinates:
Xn = Xo
Yn = Cutting Edge
Zn = Normal to Xn & Yn
NRS Planes:
πRN = Normal Reference Plane
(contains Xn & Yn)
πC = Cutting Plane
λ = 0 ; ORS = NRS πN = Normal Plane,
(perpendicular to cutting edge)
Studying Tool Angles in NRS
λ = Inclination angle
γn = Normal Rake angle
αn = Normal Clearance angle
Ф1= Auxiliary Cutting edge angle
Ф =Principal Cutting Edge angle
r = Nose radius (mm)
Tool Signature in NRS:
λ , γn , αn , αn’ , Φ1 , Φ , r (mm)
Studying Auxiliary Normal Clearance
Angle (αn’)
πn’ = Auxiliary Normal Plane
πc’ = Auxiliary Cutting Plane
αn’ = Auxiliary Normal
Clearance Angle
Designation (Signature) of Tool
Geometry
Tool Signature in ASA:
γx, γy , αx , αy’, Φe , Φs , r (inch)
Tool Signature in ORS:
λ, γo , αo , αo’ , Φ1 , Φ , r (mm)
Tool Signature in NRS:
λ , γn , αn , αn’ , Φ1 , Φ , r (mm)
Characteristics of ASA, ORS & NRS
• ASA is good for inspection,
Not for tool grinding
• ORS is good for grinding, analysis & research
Not for regrinding as additional corrections needed
• NRS is good for grinding & regrinding with no correction
requirement
Conversion of Tool Angle from one
system to another
For
• Understanding tool geometry in any reference system from available geometry
• Benefits of various systems and apply them when required
• Communicating between people using diff. systems
By
• Analytical method (geometrical) - simple but tedious
• Graphical method (master line principle) - simple, quick & popular
• Transformation matrix method- suitable for complex tool geometry (hobs,
drills, form tools etc.)
• Vector method- easy, quick, but needs knowledge of vectors)
Measuring Tool Angles in NRS
Yn
Zn πRN
B-B Cross-section πc αn
γn
πn
Zn πn
πRN
Zo Yo
B
πo Yo
λ
πc
πR B
Ф1
A
Ф
πo
A-A Cross-section A
πc
πR Xo
Measuring Auxiliary Normal Clearance
Angle (αn’)
C-C Cross-section Yn ’ Zo’
’ πo’ Zn’
Yo
πn’
D
πc ’
Zn’
πc' D πn’
C πc ’
αn’
C
πo' Yn’
Yo’ πn’
Xo’
πR D-D Cross-section
