Single Point Cutting tool

Under the action of force, pressure is exerted on the workpiece metal

causing its compression near the tip of the tool.

The metal undergoes shear type deformation and a piece or layer of metal gets repeated in the form of a chip.

Tool is continued to move relative to workpiece, there is continuous shearing of the metal ahead of the tool. The shear occurs along a plane called the shear plane.

Actual separation of the metal starts as a yielding or fracture depending upon the cutting conditions.

Deformed metal (chip) flows over the tool (rake) face.Friction between the tool rake face and the underside of the

chip is considerable , then the chip gets further deformed (i.e. secondary deformation)

Geometry of single point turning tools Single point: e.g., turning tools, shaping, planning and slotting

tools and boring tools Double (two) point: e.g., drills Multipoint (more than two): e.g., milling cutters, broaching tools,

hobs, gear shaping cutters etc. Concept of rake and clearance angles of cutting tools.The word tool geometry is basically referred to some specific angles or slope of the salient faces and edges of the tools at their cutting point.

Rake and clearance angles of cutting tools.

+

+ + +

- =0

VC

VCVC

VC

VC

R R R

Rake angle (): Angle of inclination of rake surface from reference plane clearance angle (): Angle of inclination of clearance or flank surface from the finished surface

(a) positive rake (b) zero rake (c) negative rake

Three possible types of rake angles

Rake angle is provided for ease of chip flow and overall machining

Positive rake –reduce cutting force and thus cutting power requirement. Negative rake – to increase edge-strength and life of the tool Zero rake – to simplify design and manufacture of the form tools.

Clearance angle -to avoid rubbing of the tool (flank) with the machined surface which causes loss of energy and damages of both the tool and the job surface.

Systems of description of tool geometry Tool-in-Hand System Machine Reference System – ASA system Tool Reference Systems

Orthogonal Rake System – ORS Normal Rake System – NRS Work Reference System – WRS

Tool-in-Hand System

Basic features of single point tool (turning) in Tool-in-hand system

1.salient features of the cutting tool point are identified or visualized2. No quantitative analysis

Machine Reference System(ASA system)(American standards Association)

Planes and axes of reference in ASA system

R - X - Y and Xm – Ym - Zm

R = Reference plane; plane perpendicular to the velocity vector X = Machine longitudinal plane; plane perpendicular to R and taken in the direction of assumed longitudinal feedY = Machine Transverse plane; plane perpendicular to both R and X

Tool angles in ASA system

Rake angles: x = side (axial rake: angle of inclination of the rake surface from the

reference plane (R) and measured on Machine Ref. Plane, X.

y = back rake: angle of inclination of the rake surface from the reference

plane and measured on Machine Transverse plane, Y.  Clearance angles:x = side clearance: angle of inclination of the principal flank from the

machined surface (or ) and measured on X plane.

y = back clearance: same as x but measured on Y plane. Cutting angles: [Fig. 3.5]s = approach angle: angle between the principal cutting edge (its

projection on R) and Y and measured on R

e = end cutting edge angle: angle between the end cutting edge (its projection on R) from X and measured on R

Nose radius, r (in inch) r = nose radius : curvature of the tool tip. It provides strengthening

of the tool nose and better surface finish.

Tool Reference Systems Orthogonal Rake System – ORS

R - C - O and Xo - Yo – Zo

R

C

YoXo

Xo

Yo

Zo

Planes and axes of reference in ORS

R = Refernce plane perpendicular to the cutting velocity

vector, C = cutting plane; plane perpendicular to R and taken along the

principal cutting edge

O = Orthogonal plane; plane perpendicular to both R and C

and the axes;Xo = along the line of intersection of R and O

Yo = along the line of intersection of R and C

Zo = along the velocity vector, i.e., normal to both Xo and

Yo axes.

Tool angles in ORS system

Rake angles o = orthogonal rake: angle of inclination of the rake surface from

Reference plane, R and measured on the orthogonal plane, o

= inclination angle; angle between C from the direction of assumed longitudinal feed [X] and measured on C

Clearance angleso = orthogonal clearance of the principal flank: angle of inclination of

the principal flank from C and measured on o

o’ = auxiliary orthogonal clearance: angle of inclination of the auxiliary flank from auxiliary cutting plane, C’ and measured on auxiliary orthogonal plane, o’ as indicated in Fig. 3.8.

Cutting angles = principal cutting edge angle: angle between C and the direction of

assumed longitudinal feed or X and measured on R

1 = auxiliary cutting angle: angle between C’ and X and measured on R

Nose radius, r (mm) r = radius of curvature of tool tip

Auxiliary orthogonal clearance angle

ASA system has limited advantage and use like convenience of inspection. But ORS is advantageously used for analysis and research in machining and tool performance. But ORS does not reveal the true picture of the tool geometry when the cutting edges are inclined from the reference plane, i.e., 0. Besides, sharpening or resharpening, if necessary, of the tool by grinding in ORS requires some additional calculations for correction of angles.

These two limitations of ORS are overcome by using NRS for description and use of tool geometry.

The basic difference between ORS and NRS is the fact that in ORS, rake and clearance angles are visualized in the orthogonal plane, o, whereas in NRS those angles are visualized in another plane called Normal plane, N.

orthogonal plane, o is simply normal to R and C irrespective of the inclination of the cutting edges, i.e., , but N (and N’ for auxiliary cutting edge) is always normal to the cutting edge.

Normal Rake System – NRSRN - C - N and Xn – Yn – Zn Yn

Zn

n

n

oo

YoZo o (A-A)

n (B-B)

A A

B

B

R C

n

o

Zo Zn

Xo, Xn

(a) (b)

Yo

Yno

n

R

Rake angles n = normal rake: angle of inclination angle of the rake surface from R

and measured on normal plane, N

n = normal clearance: angle of inclination of the principal flank from C and measured on N

n’= auxiliary clearance angle: normal clearance of the auxiliary flank (measured on N’ – plane normal to the auxiliary cutting edge.

Designation of tool geometry in

ASA System – y, x, y, x, e, s, r (inch)

ORS System – , o, o, o’, 1, , r (mm)

NRS System – , n, n, n’, 1, , r (mm)

   

Purposes of conversion of tool angles form one system to another

To understand the actual tool geometry in any system of choice or convenience from the geometry of a tool expressed in any other systems

To derive the benefits of the various systems of tool designation as and when required

Communication of the same tool geometry between people following different tool designation systems.

Methods of conversion of tool angles from one system to anotherAnalytical (geometrical) method: simple but

tediousGraphical method – Master line principle:

simple, quick and popularTransformation matrix method: suitable for

complex tool geometryVector method: very easy and quick but needs

concept of vectors

Conversion of tool angles by Graphical method – Master Line principle OD = TcotX

OB = TcotY

OC = Tcoto

OA = TcotWhere, T = thickness of the tool shank

Use of Master line for conversion of rake angles

OA = cot

Conversion of tool rake angles from ASA to ORS

o and (in ORS) = f (x and y of ASA system)

½ OB.OD = ½ OB.OCsin + ½ OD.Occos Dividing both sides by ½ OB.OD.OC

OBD = OBC + OCD

½ OB.OD = ½ OB.CE + ½ OD.CF

cosφtanγsinφtanγtanγ yxo

cosφtanγsinφtanγtanγ yxo

sinφtanγcosφtanγtanλ yx

cosφOB

1sinφ

OD

1

OC

1

i.e., ½ OD.AG = ½ OB.OG + ½ OB.ODwhere, AG = OAsin and OG = OAcosdividing both sides by ½ OA.OB.OD

OAD = OAB + OBD

OA

1cosφ

OD

1sinφ

OB

1

sinφtanγcosφtanγtanλ yx

y

xo

tan

tan

sincos

cossin

tan

tan

Conversion of rake angles from ORS to ASA system x and y (in ASA) = f(o and of ORS)

cosφtansinφtanγtanγ ox

sinφtancosφtanγtanγ oy

ML of principal flankML of auxiliary flank

Fig. Master lines (ML) of flank surfaces

Conversion of clearance angles from ASA to ORS

Fig. Master line of principal flank

tann = tanocos

cotn'= coto'cos'

cosφy

cotαsinφx

cotαo

cotα

sinφy

cotαcosφx

cotαtanλ

y

xo

cot

cot

sincos

cossin

tan

cot

Conversion of tool angles from ORS to NRS

, o, o, o’, 1, , r (mm) – ORS

, n, n, n’, 1, , r (mm) – NRS

cotn = cotocos