Department of Mechanical
and Materials Engineering
MECH 211
Lecture 5 – Machining III
(Drilling)
September 12, 2023
Page 1
In this lecture we learn about:
 Various forms of drilling operations
 Drill geometry and terminology
 Chip formation in drilling
 Operational sequences
 Machinery configurations
Relevant sections in text book:
23.5 23.6
September 12, 2023
Page 2
Introduction
Various types of drills, drilling and reaming operations.
September 12, 2023
Courtesy of S. Schmidt
Page 3
Drill Geometry and Terminology
Drilling is carried out on a: Drill press, Lathe, Mill, Flexible Manufacturing
The most commonly used tool is the “Twist Drill”.
w
V= w R
The “business end” of the drill has:
[SFM]
 Two cutting edges & a chisel point (drill point)
 A Helix; helix angle.
 The cutting “rake angle” is controlled by the helix angle.
 The rake angle changes along the cutting edge
because the helix is continuously changing.
w
 Chips slide up the flute.
Courtesy Paul. K. Wright. UC Berkley.
Metal Cutting, 4th Edition© 2000 Butterworth-Heinemann
September 12, 2023
Page 4
Drill Geometry and Terminology
Cutting edges
flute
N
N
Drill point
N
Helix
angle
Drill point
Rake
Face
Drill point
angle = 118o
The drill cutting edge has a varying shape;
It has a varying rake angle, a, along the cutting
edge.
The rake angle goes from - to + by
moving away from the drill point.
September 12, 2023
a
+
Page 5
Drilling Operations – Chip formation
Important conditions during chip formation:
 The chip generation is hidden and invisible;
 There is limited space for chip removal, along the flutes;
 There is friction between the tool, chip and workpiece creating a
lot of heat
 The cutting speed is variable, from 0 at the centre to a maximum
at the outer edge.
These can have a negative effect upon tolerance & surface
roughness
How to improve :
 Coolant can help increase heat dissipation rate from the drill bit
 Keep the cutting edge sharp to minimize friction and heat
 Matching the right drill material and geometry to the material
being drilled.
September 12, 2023
Page 6
Drilling Sequences – Example for precise hole making
Reaming: performs the final
cutting operation on holes,
particularly holes with close
tolerances.
September 12, 2023
1.
2.
3.
4.
5.
Centre drill
Drill,
Countersink
or Counterbore,
Ream,
Page 7
Drilling Example
N
d
A hole is being drilled in a block of
magnesium alloy with a 10 mm f drill bit,
at a feed, f = 0.2 mm/rev,
 πD 2 
 fN with a spindle speed of N = 800 rpm.
MRR  
 4 
What is the metal removal rate and
the torque on the drill?
N
V
πD
f
D
118o
N: spindle rotational speed, rpm
10 mm f.0.393 in)
f: feed, mm/rev
0.2 mm/rev
d: hole depth, mm
(0.008 in/rev)
MRR: metal removal rate
800 rpm
 π 10mm 2   mm  
 mm 3 
 mm 3 
1) MRR  
800 rpm   12570
 0.2 
  210


min
s
4
rev






 
2) power = ?
 mm 3 
power  210
  ?  ?W 
 s 
Joule
September 12, 2023
W  s 
 mm 3 


Unit energy, u, for
machining magnesium
Page 8
Drilling Example – continued
Power (W) =
Torque (N.m) x Rotational Speed (rad/sec)
𝝎 = 𝟐𝝅𝑵
September 12, 2023
Page 9
Sample Question
True or False: The cutting speed, V, during drilling operations is
(a)
(b)
(c)
(d)
(e)
a function of rotational speed, ω
controlled by rake angle, α
controlled by helix angle, δ
a function of feed rate, f
a function of drill bit radius, R
September 12, 2023
Page 10
1042
2 thou tolerance
Drilling Sequences
Boring tool
Example:
“Four cut” boring of a drive hub.
cuts 1 & 2
cut 3
DOC, d 3.8 mm
cut 4
DOC, d 3.8 mm
DOC, d 0.32 mm
September 12, 2023
bar stock
in rad/sec
surface
Page 11
Drilling Machinery – Standard Drill manual press
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Page 12
Special Drilling Situations - Drills with Inserts
Cutting tool
chamfer
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Page 13
Special Drilling Situations - Trepanning
Courtesy of S. Schmidt
(a) Trepanning tool. (b) Trepanning with a drill-mounted single cutter.
September 12, 2023
Page 14