This document discusses the geometry of plain milling cutters and twist drills. It describes the key features of milling cutters such as radial rake angle, radial relief angle, land, and lip angle. It also explains different types of milling operations including up milling, down milling, string milling, and gang milling. For twist drills, it outlines the drill point, twist drill nomenclature, and recommended drill geometries for different materials. Equations are provided for estimating drilling forces based on drill diameter and feed rate.

1. Geometry of Plain Milling Cutter
&
Geometry of Twist Drill
BY –BY –GIRISH SAPRA
Department of Mechanical EngineeringDepartment of Mechanical Engineering
NITTTR , CHANDIGARHNITTTR , CHANDIGARH
March, 2016March, 2016

2. Objectives
• Understand the characteristic features of the
milling process
• Select the various types of milling cutters
based on the application
• Understand the different types of milling
operations that can be done in the milling
machines

3. Milling
• In milling, the workpiece is fed into a rotating
milling cutter, which is a multi-point tool
• Interrupted cutting
• Small size of chips
• Variation in chip thickness

4. Milling operation

5. Milling Machine

6. Milling Cutters
• Based on construction
Solid
Inserted tooth type
• Based on mounting
Arbour mounted
Shank mounted

7. Milling Cutters
• Base on rotation
Right hand rotation (Counter clockwise)
Left hand rotation (Clockwise)
• Based on helix
Right hand helix
Left hand helix

8. Milling Cutters

9. Geometry of Plane Milling Cutter

10. Geometry of Plane Milling Cutter
• Radial Rake Angle
• Radial Relief Angle
• Land
• Flute
• Heel
• Fillet
• Lip angle

11. Up Milling
• In up milling the cutting tool rotates in the
opposite direction to the table movement.
• In the conventional or up milling, the chip
starts as zero thickness and gradually
increases to the maximum size.
• However, this process is inherently safe.

12. Down Milling (Climb Milling)
• In down milling the cutting tool rotates in the
same direction as that of the table movement.
• In the climb or down milling, the chip starts as
maximum thickness and goes to zero
thickness gradually.
• The cutting force will act downwards and as
such would keep the workpiece firmly in the
work holding device.
• This is good for thin and frail workpieces.

13. Up and Down Milling

14. String Milling
• A number of the workpieces will be kept on
the machine table in a line and hence called as
'string milling' or 'line milling'.
• By having a number of workpieces kept in line
the approach distance will be only at the
beginning and end of the line, thus
considerably saving the machine time.

15. Gang Milling
• In gang milling a number of milling cutters are
fastened to the arbor to suit the profile of the
workpiece to be machined.
• For example, two side and face milling cutter
with a slab milling cutter at the centre to mill
an inverted U-shape.
• The advantage of gang milling is that several
surfaces are machined at the same time.

16. Gang Milling

17. Geometry of Twist Drill

18. Twist Drill
• A rotating cutting tool, used for
cutting holes in rigid materials, that consists of
an essentially conical point, relieved
and fluted to form cutting lips, and spiral
flutes which direct the chips away from the
lips and toward ejection from the hole.

19. Twist drill

20. Drill geometry

21. Drill point

22. Twist drill nomenclature
• AXIS - The imaginary straight line which forms
the longitudinal center line of the drill.
• BODY - The portion of the drill extending from
the shank or neck to the outer corners of the
cutting lips.
• CHISEL EDGE ANGLE - The angle included
between the chisel edge and the cutting lip, as
viewed from the end of the drill.
• DRILL DIAMETER - The diameter over the
margins of the drill measured at the point.

23. Contd...
• FLUTES - Helical or straight grooves cut or formed in
the body of the drill to provide cutting lips, to permit
removal of chips, and to allow cutting fluid to reach
the cutting lips.
• FLUTE LENGTH - The length from the outer corners of
the cutting lips to the extreme back end of the flutes.
• HELIX ANGLE - The angle made by the leading edge of
the land with a plane containing the axis of the drill.
• LIPS - The cutting edges of a two flute drill extending
from the chisel edqe to the periphery.

24. Contd..
• POINT - The cutting end of a drill, made up of the ends of the lands
and the web. In form it resembles a cone, but departs from a true
cone to furnish clearance behind the cutting lips.
• POINT ANGLE - The angle included between the lips projected upon
a plane parallel to the drill axis and parallel to the cutting lips.
• SHANK - The part of the drill by which it is held and driven.
• TANG - The flattened end of a taper shank, intended to fit into a
driving slot in a socket.
• TANG DRIVE - Two opposite parallel driving flats on the extreme
end of a straight shank.
• WEB -The central portion of the body that joins the lands. The
extreme end of the web forms the chisel edge on a two-flute drill.

25. Twist Drill Geometry
• In order to provide strength to the drill the
cutting edge is thickened gradually from the
bottom. It is termed as web.
• The web will only compress the material and
as a result, the thrust on the drill increases
with an increase in the web thickness.
• Also it is likely that out of round and over size
holes may result in because of the additional
thrust.

26. • The best geometry to use depends upon the
properties of the material being drilled. The
following table lists geometries recommended
for some commonly drilled materials.

27. • A more aggressive angle, such as 90 degrees, is suited
for very soft plastics and other materials. Such a bit is
generally self-starting and can cut very quickly.
• A shallower angle, such as 150 degrees, is suited for
drilling steels and other tougher materials. This style of
drill requires a starter hole, but does not bind or suffer
premature wear so long as a suitable feed rate is used.
• Drill bits with no point angle are used in situations
where a blind, flat-bottomed hole is required.

28. Drilling Force Estimation
• The torque acting on a twist drill is
M = C d1.9f0.8N-mm
d is the diameter of the drill in mm
f is the feed rate of the drill in mm/rev
C is a constant
• The thrust force is
T = K d f0.7 Newtons
• The values of K are given as
• Steel = 84.7, Cast iron = 60.5

29. References.
• Bhattacharya A., “Metal Cutting” Central
Publishers, Kolkata,2000 140-145
• Donaldson, “Tool Design ”Tata- McGraw Hill ,
3rd
Edition,2000,PP.5OO-515
• Rajput, R. K. A textbook of Manufacturing
technology.1. New Delhi: Luxmi Publishers (P)
Ltd,2007,pp. 80-92.