Side cutting edge angle.

The following are the advantages of increasing the angle.

• It increases tool life as, for the same depth of cut, the cutting force is distributed on a wider surface.

• It diminishes the chip thickness for the same amount of feed and permits greater cutting speed.

• It dissipates heat quickly for having wider cutting edge.

• This side cutting edge angle of the tool has practically no effect on the value of cutting force or power consumed for a given depth of cut and feed.

• Large side cutting edge angles are lightly to cause the tool to chatter.

End cutting edge angle.

The function of end cutting edge angle is to prevent the trailing front cutting edge of the tool from rubbing against the work. A large end cutting edge angle unnecessarily weakens the tool. It varies from 8 to 15 degrees.

IMPORTANCE OF NOSE RADIUS.

The nose of a tool is slightly rounded in all turning tools.

• Greater nose radius clears up the feed marks caused by the previous shearing action and provides better surface finish.

• All finish turning tool have greater nose radius than rough turning tools.

• It increases the strength of the cutting edge, tends to minimize the wear taking place in a sharp pointed tool with consequent increase in tool life.

• Accumulation heat is less than in a pointed tool which permits higher cutting speeds.

TOOL POINT REFERENCE SYSTEM.

To determine the orientation and inclination of the rake face and flank surfaces, a coordinate system is essential, resulting in a set of planes with references to which the orientation or inclination can be determined. Two planes are of significance.

• Tool reference plane or principal plane, which is perpendicular to the cutting velocity vector.

• Cutting plane, which is tangential to the cutting edge and contains the velocity vector. The cutting plane is also perpendicular to the principal plane or the tool reference plane.

There are three different types of coordinate system that are popular, when it comes to tool nomenclature, they are:

[1] Machine Reference System (MRS)

[2] Orthogonal tool Reference System (ORS)

[3] Oblique or Normal tool Reference System (NRS)

MACHINE REFERENCE SYSTEM – MRS

This system is also called ASA system, ASA stands for American Standards Association. Geometry of a cutting tool refers mainly to its several angles or slope of its salient working surfaces and cutting edges. Those angles are expressed w.r.t. some planes of reference. In Machine Reference System (ASA), the three planes of reference and the coordinates are chosen based on the configuration and axes of the machine tool concerned.

For example In a Lathe, XX is the spindle axis or work piece axis, YY is the tool axis and ZZ is the vertical axis. Figure 1 depicts the xyz coordinates of machine.

The planes of reference and the coordinates used in ASA system for tool geometry are:

$\pi_R - \pi_x - \pi_Y \ and \ X_m – Y_m – Z_m$

$\pi_R$ = Reference plane, plane perpendicular to the velocity vector.

$\pi_x $ = Machine longitudinal plane, plane perpendicular to $\pi_R$ and taken in the direction of assumed longitudinal feed.

$\pi_Y $ = Machine Transverse plane, plane perpendicular to both $\pi_R \ and \ \pi_x$ [This plane is taken in the direction of assumed cross feed]

The axes $X_m, \ Y_m \ and \ Z_m$ are in the direction of longitudinal feed, cross feed and cutting velocity (vector) respectively.

$\gamma_X$ = Side (axial rake: angle of inclination of the rake surface from the reference plane ($\pi_R$) and measured on Machine Ref. Plane, $\pi_X$

$\gamma_Y$ = back rake: angle of inclination of the rake surface from the reference plane and measured on Machine Ref. Plane, $\pi_Y$

- Clearance angles:

$\alpha_x$ = side clearance: angle of inclination of the principal flank from the machined surface (or $ \bar {V_c}$) and measured on $\pi_X$ plane.

$\alpha_y$ = back clearance: same as $\alpha_x$ but measured on $\pi_y$ plane.

- Cutting angles:

$\pi_s$ = approach angle: angle between the principal cutting edge (its projection on $\pi_R$) and $\pi_y$ and measured on $\pi_R$

$\pi_e$ = end cutting edge angle: angle between the end cutting edge (its projection on $\pi_R$) and $\pi_x$ and measured on $\pi_R$

- Nose radius, r (in inch)

r = nose radius: curvature of the tool tip. It provides strengthening of the tool nose and better surface finish.

The shape of the tool is normally specified in a special sequence, often referred to as tool signature as shown below:

• Back rake angle.

• Side rake angle.

• Front or end clearance or relief angle.

• Side clearance angle or relief angle.

• End cutting edge angle.

• Side cutting edge angle.

• Nose radius.

ORTHOGONAL TOOL REFERENCE SYSTEM – ORS.

Generally referred to as ORS (Orthogonal rake system). This system is also known as ISO (International standard organization) – old.

• The principal or tool reference plane, $\pi_R$, which is the same as for the machine reference plane.

• The cutting plane $\pi_c$, which contains the cutting edge, normal to $\pi_R$ plane

• The cutting plane $\pi_o$, which contains the cutting edge, normal to $\pi_R$ plane

Figure 3 shows the orientation of the rake face and flank surfaces with respect to the orthogonal tool reference system and tool angles in symbolic form.

$X_o $ = along the line of intersection of $\pi_R$ and $\pi_O$

$Y_o $ = along the line of intersection of $\pi_R$ and $\pi_C$

$Z_o$ = along the velocity vector, i.e., normal to both $X_o $ and $Y_o $ axes.

The main geometrical angles used to express tool geometry in Orthogonal Rake System (ORS) and their definitions will be clear from figure 4.

$\lambda$ = inclination angle, angle between $\pi_C$ from the direction of assumed longitudinal feed [$\pi_X$] and measured on $\pi_C$

- Clearance angles.

$\alpha_o$ = orthogonal clearance of the principal flank: angle of inclination of the principal flank from $\pi_C$ and measured on $\pi_o$

$\alpha_o$’ = auxiliary orthogonal clearance, angle of inclination of the auxiliary flank from auxiliary cutting plane, $\pi_C$’ and measured on auxiliary orthogonal plane, $\pi_o$’ as indicated in Fig 5.

- Cutting angles.

$\pi$ = principal cutting edge angle, angle between $\pi_c$ and the direction of assumed longitudinal feed or $\pi_x$ and measured on $\pi_R$

$\phi_1$ = auxiliary cutting angle, angle between $\pi_C$’ and $\pi_x$ and measured on $\pi_R$

- Nose radius, r (mm)

r = radius of curvature of tool tip.

Definition of –

- Rake angles

$\gamma_o$ = orthogonal rake, angle of inclination of the rake surface from Reference plane, $\pi_R$ and measured on the orthogonal plane, $\pi_o$

NORMAL RAKE SYSTEM – NRS.

This system is also known as oblique reference system or ISO – new.

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., $\lambda \neq 0$ 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, $\pi_o$, whereas in NRS those angles are visualized in another plane called Normal plane, $\pi_N$. The orthogonal plane, $\pi_o$ is simply normal to $\pi_R$ and $\pi_C$ irrespective of the inclination of the cutting edges, i.e., $\lambda$, but $\pi_N$ (and $\pi_N$’ for auxiliary cutting edge) is always normal to the cutting edge. The differences between ORS and NRS have been depicted in below figure.

The planes of reference and the coordinates used in NRS are:

$\pi_{RN} - \pi_C - \pi_N \ and \ X_n - Y_n – Z_n $

Where,

$\pi_{RN} $ = normal reference plane

$\pi_N $ = Normal plane, plane normal to the cutting edge.

$X_n = X_c$

$Y_n$ = cutting edge.

$Z_n$ = normal to $ X_n $ and $Y_n$

It is to be noted that when $\lambda = 0$, NRS and ORS become same, i.e. $\pi_o \cong \pi_N , Y_N \cong Y_o$ and

$Z_n \cong Z_o$

Definition (in NRS) of

- Rake angles

$\gamma_n$ = normal rake, angle of inclination angle of the rake surface from $\pi_R$ and measured on normal plane, $\pi_N$

$\alpha_n$ = normal clearance: angle of inclination of the principal flank from $\pi_C$ and measured on $\pi_N$

$\alpha_n$’ = auxiliary clearance angle: normal clearance of the auxiliary flank (measured on $\pi_N$’ – plane normal to the auxiliary cutting edge.

The cutting angles, $\phi$ and $\phi_1$ and nose radius, r (mm) are same in ORS and NRS.

- ASA System –

$\gamma_y, \gamma_x, \alpha_y, \alpha_x, \phi_e, \phi_s, r$ (inch)

- ORS System –

$\lambda, \gamma_o , \alpha_o, \alpha_o,’ \phi_1, \phi, r$ (mm)

- NRS System –

$\lambda, \gamma_n, \alpha_n, \alpha_n’, \phi_1, \phi, r$ (mm)