IPE 4101

Machine Tools and Machining

Cutting Tool Geometry

Dr. M. Azizur Rahman

Acknowledgement PhD (NUS, Singapore), MSc (NTU, Singapore), MEng (NUS, Singapore), BSc Eng (BUET),
Prof. A.K.M. Nurul Amin MIEB(Life), MIMechE, CEng(UK)

Assistant Professor
Dept. of Mechanical and Production Engineering
1
Ahsanullah University of Science and Technology (AUST)
• In the metal cutting operation, the tool is wedge-
shaped and has a straight cutting edge.

• Basically, there are two methods of metal cutting,

depending upon the arrangement of the cutting
edge with respect to the direction of relative work-
tool motion:

• Orthogonal cutting or 2D cutting

• Oblique cutting or 3D cutting.

2
Orthogonal/Oblique Machining

Orthogonal Machining Oblique Machining

Fig. Orthogonal and Oblique Machining

3
Orthogonal cutting: 2D Cutting edge is perpendicular to the
direction of relative work-tool motion.

Being 2D, it simplifies research

investigation of the metal cutting
process and therefore widely
used in theoretical and
experimental work.

4
Orthogonal Cutting
❑ The cutting edge of the tool
remains at 900 to the direction of
feed (of the tool or the work).
❑ The chip flows in a direction
normal to the cutting edge of the
tool
❑ The chip flows in the plane of the
tool face.
❑ The shear force acts on a smaller
area, so shear force per unit area
is high.

5
Oblique Cutting
• The cutting edge of the tool remains
inclined at an acute angle to the
direction of feed (of the work or tool).
• The cutting edge is inclined at an angle
λ to the normal to the feed. This angle
is called inclination angle.

6
 https://www.sandvik.coromant.com

Figure A range of cutting tool materials: CS,

coated sintered carbides; C1, aluminium oxide
(white) ceramics; C2, mixed (black) ceramics;
C3, silicon nitride-based ceramics; CT, cermets;
PCBN, polycrystalline cubic boron nitride
according CeramTec and Sandvik Coromant.

Source: Internet at www.secotools.com;

www.sandvik.coromant.com; www.guhring.com; www.argor-
aliba.com; www.ceramtec.com.
8
Cutting Tool Geometry
• Cutting tool is a device with which a material could be cut to the desired size, shape or
finish.
• So a cutting tool must have at least one sharp edge. There are two types of cutting tool.
• The tool having only one cutting edge is called single point cutting tools.
• For example shaper tools, lathe tools, planer tools, etc.
• The tool having more than one cutting edge is called multipoint cutting tools. For example
drills, milling cutters, broaches, grinding wheel honing tool, etc.

9
Cutting Tool Geometry
A single point cutting tool may be either right or left hand
cut tool depending on the direction of feed.

Primary Cutting Edge

Left hand cutting Right hand cutting

tool tool

Fig. Tool for Left Hand and Right hand cutting

10
Tool-in-hand Nomenclature

Fig. Nomenclature of Tool and cutting surfaces

11
Fig. Tool Nomenclature of a single point cutting tool

12
• The cutting tool consists of the
following elements:
• face or rake surface,
• flank,
• cutting edges and
• the tip/nose/corner.

◼ Face or rake surface is the surface of the cutting tool along

which the chips flow out.
◼ Flank surfaces are those facing the work piece. There are two
flank surfaces:
 principal and
 auxiliary flank surfaces. 13
• Principal cutting edge performs the
major portion of cutting and is
formed by intersecting the face with
the principal flank surface.
• Auxiliary cutting edge (often called
end cutting edge) is formed by the
intersection of the rake surface with
the auxiliary flank surface.
• Corner/nose or cutting point is the
meeting point of the principal
cutting edge with the auxiliary
cutting edge.

14
Geometry of Single Point Cutting Tool
• Shape of the cutting tool is defined either in the:
• Tool Reference system, or
• Machine Reference system
• Analysis of the tool shape includes:
• Location of the cutting edges with respect to the chosen
reference system.
• Orientation of the face and flank surfaces with respect to
the chosen reference system.
 Location of cutting edges are defined with respect to the
machine and tool reference systems.

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Tool Nomenclature/Angles
The basic elements of a single point cutting tool

17
Tool-in-Hand System for Tool Angles

Tool-in-Hand System
is used to describe the geometry of a
cutting tool when it is NOT in use in a
cutting process.

18
Tool-in-Hand System for Tool Angles
Tool-in-Hand System for Tool Angles
Reference planes:
Pr Pf Pp

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The 6 reference planes in tool-in-hand system
• Reference plane Pr – parallel to the tool base or
perpendicular to the assumed cutting velocity
direction.
• Working plane Pf – parallel to the assumed feed
velocity direction.
• Back plane Pp – perpendicular to both Pr and Pf.
• Side cutting plane Ps – perpendicular to Pr and
tangential to the major cutting edge.
• Orthogonal plane Po – perpendicular to Pr and Ps.
• Normal plane Pn – normal to the major cutting edge.

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Tool-in-Hand System for Tool Angles
Reference planes:
Ps Po Pn

22
The 5 Tool Angles in tool-in-hand system

• Tool rake angle  - angle between tool rake face and

Pr
• Orthogonal rake angle o – measured in Po plane,
angle between tool rake face and Pr.
• Normal rake angle n – measured in Pn plane, angle
between tool rake face and Pr.
• Side rake angle f – measured in Pf plane, angle
between tool rake face and Pr.
• Back rake angle p – measured in Pp plane, angle
between tool rake face and Pr.

23
The 5 Tool Angles in tool-in-hand system

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 The 5 Tool Angles in tool-in-hand system

• Tool relief angle,  - angle between tool flank face and

Ps

• Orthogonal relief angle o – measured in Po plane,

angle between tool flank face and Ps.
• Normal relief angle n – measured in Pn plane, angle
between tool flank face and Ps.
• Side relief angle f – measured in Pf plane, angle
between tool flank face and Ps.
• Back relief angle p – measured in Pp plane, angle
between tool flank face and Ps.
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The 5 Tool Angles in tool-in-hand system

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 The 5 Tool Angles in tool-in-hand system

• Tool inclination  - measured within Ps, angle between

the major cutting edge and Pr.
• Tool side cutting edge angle s - angle between Pp and
the major cutting edge.
• Tool approach angle Kr - angle between the major
cutting edge and Pf, Kr = 90o - s.
• Tool end cutting edge e – angle between Pf and the
end cutting edge.

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The 5 Tool Angles in tool-in-hand system

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Sign conventions for the rake angle and inclination angle

• Positive rake angle – the

rake face is below Pr;
• Negative rake angle –
the rake face is above Pr.
• Positive inclination
angle – the major
cutting edge is above Pr;
Negative inclination
angle – the major
cutting edge is below Pr.

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Geometry of Single Point Cutting Tool

Fig. Angle of inclination of the side

(main) cutting edge

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Geometry of Single Point Cutting Tool

Xm+
Xm+

+
Zm+Zm

Xm+ Z +
m

+
Zm

Ym+

Ym+

Fig. Tool Angles in Longitudinal and Transverse planes

31
Geometry of Single Point Cutting Tool

• Side rake angle (γlg or f ) – measured in Pf plane, angle between tool rake face
and Pr.
• Side relief angle (αlg or f ) – measured in Pf plane, angle between tool flank face
and Ps.
• Back relief angle (αtr or p )– measured in Pp plane, angle between tool flank face
and Ps.
• Back rake angle (γtr or p )– measured in Pp plane, angle between tool rake face
and Pr.
• Tool approach angle (φ or Kr)- defined as the angle between the projection of the
principal cutting edge Pf, Kr = 90o - s.

32
Tool signature

33
 TOOL SIGNATUR/ENOMENCLATLURE
The tool signature or nomenclature for a single-point tool is a sequence of alpha and numeric
characters representing the various angles, significant dimensions, special features, and size of the nose
radius.
This method of identification has been standardized by the American National Standards Institute (ANSI)
for carbide and HSS.

Figure: A straight-shank, right-cut, single-point

tool, illustrating the elements of the tool
signature as designated by ANSI. Positive rake
angles are shown.
 TOOL SIGNATUR/ENOMENCLATLURE
Back-rake Angle: It is the angle between the face of the tool and a line parallel to the base of the
toolholder. It is measured in a plane parallel to the side-cutting edge and perpendicular to the base.
• Variations in the back-rake angle affect the direction of chip flow and cutting force.
• As this angle is increased while other conditions remain constant, tool life will increase slightly and the
required cutting force will decrease.
• Cutting-edge strength decreases dramatically as positive back-rake angles are increased above 5°.
• Similarly, cutting-edge strength increases as back rake becomes negative and is optimized at around –5°.
Side-rake Angle: It is the angle between the tool face and a plane parallel to the tool base. It is measured in
a plane perpendicular to both the base of the holder and side-cutting edge.
• Variations in this angle have the largest effect on cutting force and, to some extent, affect direction
of chip flow. As the angle is increased, forces are reduced about 1% for each degree of positive side rake
and less tearing of the workpiece occurs.
• Negative side rake increases edge strength and is recommended for most steels.
TOOL SIGNATUR/ENOMENCLATLURE
End-relief Angle: End-relief angle is between the end flank and a line perpendicular to the base of the
tool.
• The purpose of this angle is to prevent rubbing between the workpiece and the end
flank of the tool.
• An excessive clearance or relief angle reduces the strength of the tool, so the angle
should not be larger than necessary; it is typically in the 5–7° range.

Side-relief Angle: It is between the side flank of the tool and a line drawn perpendicular to the base.
• Comments regarding end-relief angles are applicable to side clearance or relief angles as well.
• For turning operations, the side-relief angle must be large enough to prevent the tool from advancing
into the workpiece before the material is machined away. Angles of 5–7° are sufficient for a feed ratio
under 0.8 mm per revolution.
• Threading of low-pitch threads requires up to 25° clearance.
TOOL SIGNATUR/ENOMENCLATLURE
End-cutting-edge Angle: The end-cutting-edge angle is between the edge on the end of the tool and
a plane perpendicular to the side of the tool shank.
• The purpose of the angle is to avoid rubbing between the edge of the tool and the workpiece.
• As with end-relief angles, excessive end-cutting-edge angles reduce tool strength with no added
benefit.

Lead Angle (Side-cutting-edge Angle): It is the angle between the straight cutting edge on the side of
the tool and the side of the tool shank.
• This side edge provides the major cutting action and should be kept as sharp as possible.
Increasing the lead angle tends to widen and thin the chip, and influences the direction of chip
flow.
• An increase in the side-cutting-edge angle reduces the chip thickness for a given feed by a factor
of the cosine of the angle. This, in effect, reduces the chip contact width to thin out the built-up
edge.
• An excessive side-cutting-edge angle redirects feed forces in the radial direction, which may cause
chatter. As the angle is increased from 0 to 45°, workpiece entry is moved away from the
vulnerable tip (radius) of the tool to a stronger, more fully supported part of the tool, usually
resulting in increased tool life. However, these benefits usually will be lost if chatter occurs, so an
optimum maximum angle should be sought.
TOOL SIGNATUR/ENOMENCLATLURE
Nose radius: The nose radius connects the side- and end cutting edges and dramatically affects tool
life, radial force, and surface finish.
• Sharp, pointed tools have a nose radius of zero.
• Increasing the nose radius from zero avoids high heat concentration at a sharp point.
• Improvements in tool life and surface finish usually result as the nose radius is increased up to 1.6
mm.
• An increase in nose radius has the same general effect as increasing the side-cutting-edge angle.
The shape of the contact area changes, but at the point of contact between the machined surface
and tool, the chip is very thin. In comparison, the feed marks and resultant surface finish are
much smoother than those left by a sharp nosed tool.
• There is a limit to radius size that must be considered. Chatter and poor surface finish will result if
the nose radius is too large; an optimum maximum value should be sought.
TOOL SIGNATUR/ENOMENCLATLURE
Nose radius:
• There is a correlation between ideal surface roughness, nose radius, and feed, which is given by:

0.321𝑓 2
𝑅𝑎 =
𝑟𝑒
where:
Ra = surface roughness (mm), f = feed (mm), and re = nose radius (mm).
 TOOL SIGNATUR/ENOMENCLATLURE
• Shank: The portion of the tool bit which is not
ground to form cutting edges and is rectangular in
cross section.
• Face: The surface against which the chip slides
upward. Nose radius

• Flank: The surface which face the work piece. There

are two flank surfaces in a single point cutting tool.
One is principal flank and the other is auxiliary flank.
• Heel: The lowest portion of the side cutting edges.
Heel
• Nose radius: The conjunction of the side cutting edge
and end cutting edge. It provides strengthening of
the tool nose and better surface finish.
• Base: The underside of the shank.
Recommended angles for carbide, single-point tools
Recommended angles for cast alloy single-point tools*
TOOL SIGNATUR/ENOMENCLATLURE
Multiple-point Cutting tools:
• Multiple-point cutting tools comprise a series of single-point tools mounted in or integral with a
holder or body and operated in such a manner that all the teeth (tools) follow essentially the same
path across the workpiece.
• The cutting edges may be straight or in the form of various contours to be reproduced on the
workpiece.
• Multiple-point tools may be either linear travel or rotary.
• With linear travel tools, the relative motion between the tool and workpiece is along a straight-line
path.
• The teeth of rotary cutting tools revolve about the tool axis. The relative motion between the
workpiece and a rotary cutting tool may be either axial or in a plane normal to the tool axis.
• In some cases, a combination of the two motions is used. Certain form-generating tools involve a
combination of linear travel and rotary motions.
• Cutting processes for multiple-point tools are similar to those for single-point tools.
Figure: A face milling cutter with inserted
teeth. All pertinent tooth angles are
included.
Nomenclature for twist drills
Hole broach details