Drilling process

1. By Baskaran

2. Drilling is a process of making holes on
workpieces.
The tool used for drilling is a drill and it is
rotated with a downward pressure causing
the tool to penetrate into the material.
Drilling Process

3. • Flat or spade drill
• Straight fluted drill
• Twist drills
Types of Drills

4. This type of drill is used where the
required size of twist drill is not available.
Flat Drill

5. It is made from a round tool steel piece
which is forged to shape and ground to
size, and then hardened and tempered.
This type of drill is used for hand drilling
(without power) or with a ratchet brace

6. It has grooves or flutes running parallel to
the drill axis.
Straight fluted drill

7. It is mainly used in drilling brass, copper or
soft materials.
This type of drill is inconvenient in standard
practice, as the chips do not come out from
the hole automatically.
It is used to drill sheet metals and cores in
the castings.

8. In this type, two spiral flutes or grooves run
lengthwise around the body of the drill.
Spiral fluted drill

9. It is the most common type of drill used for
all purposes, and especially for faster
drilling of accurate holes and for harder
materials in comparison with the other
drills

10. Point
The cone shaped end, which does the
cutting, is called the point.
It consists of a dead center, lips or cutting
edge and a heel.
Elements of Drill Bit

11. Tang
This is provided only on taper shank drills,
for driving (giving torque to) the drill, which
when overloaded, becomes twisted or gets
sheared off.

12. Flutes
Flutes are the spiral grooves which run to
the length of the drill.
The flutes help:
• To form the cutting edges
• To cur) the chips and allow these to come
out
• The coolant to flow to the cutting edge.

13. Shank
This is the driving end of the drill which is
fitted on to the machine.
Shanks are of two types.
Taper shank, with Morse taper provided, is
used for larger diameter drills, and the
straight shank is used for smaller diameter
drills.

14. Land/margin
The land/margin is the narrow strip which
extends to the entire length of the flutes.
The diameter of the drill is measured
across the land/margin.

15. Body clearance
Body clearance is that part of the body
which is reduced in diameter to cut down
the friction between the drill and the hole
being drilled

16. Web
Web is the metal column, which
separates the flutes.
It gradually increases in thickness
towards the shank.

17. Twist drills, used in a machine shop, are
usually made out of high-speed steel.
For drilling hard materials at higher
cutting speeds, there are drills with
carbide tips, brazed at the lips of the drill.
Material for Twist Drill

18. Drill (Parts and Functions)
Drilling is a process of making holes on
workpieces.
The tool used is a drill.
For drilling, the drill is rotated with a
downward pressure causing the tool to
penetrate into the material.
Drill (Parts and Functions)

19. The various parts of a drill can be identified
from figure .
Parts of a Drill

20. Point
The cone shaped end, which does the
cutting, is called the point. It consists of a
dead centre, lips or cutting edges, and a
heel.

21. Tang
This is a part of the taper shank drill,
which fits into the slot of the drilling machine
spindle.

22. Shank
This is the driving end of the drill, which
is fitted on to the machine. Shanks are
of two types.
Taper shank, used for larger diameter
drills, and straight shank, used for
smaller diameter drills.

23. Body
The portion between the point and
the shank is called the body of a
drill.
The parts of the body are flute,
land/margin, body clearance and
web.

24. Flutes
Flutes are the spiral grooves, which run
to the length of the drill.
The flutes help
To form the cutting edges
To curl the chips and allow these to come
out
The coolant to flow to the cutting edge.

25. Land/Margin
The land/margin is the narrow strip,
which extends to the entire length of the
flutes.
The diameter of the drill is measured
across the land/ margin.

26. Like all cutting tools the drills are provided
with certain angles for efficiency in drills.

27. Angles
They are different angles for different
purposes. They are listed below.
Point angle, Helix angle, Rake angle.
Clearance angle and Chisel edge angle.

28. Point angle/cutting angle
The point angle of a general purpose
(standard) drill is 118°. This is the angle
between the cutting edges (lips). The angle
varies according to the hardness of the
material to be drilled

29. Twist drills are made with different
helix angles. The helix angle determines
the rake angle at the cutting edge of the
twist drill.
The helix angles vary according to the
material being drilled. According to
Indian Standards, three types of drills are
used for drilling various materials.

30. Type N - for normal low carbon steel.
Type H - for hard and tenacious materials.
Type S -for soft and tough materials

31. Rake angle
Rake angle is the angle of the flute
(helix angle).

32. Clearance angle
The clearance angle is to prevent the
friction of the tool behind the cutting edge.
This will help in the penetration of the cutting
edges into the material. If the clearance
angle is too much. The cutting edges will be
weak find if it is too small, the drill will not
cut.

33. Chisel Edge Angle/Web Angle
This is the angle between the chisel edge
and the cutting lip.
• Designation of drills
• Twist drills are designated by the
• Diameter
• Tool type
• Material.

34. Example
A twist drill of 9.5 mm dia. of tool type 'H'
for right hand cutting and made from HSS is
designated as
Twist drill 9.50 - H - IS5101 - HS Diameter
of drill ,IS No. , Tool type, Material.

35. • Oversized holes
• Overheated drills
• Rough Holes
• Unequal and interrupted flow of chips
• Split webs or broken drills
Defects of Drilling operation

36. • Unequal length of cutting edges
• Unequal angle of cutting edges
• Unequal point thinning
• Spindle running out of center
• Drill point not in centre
Oversized Holes

37. • Cutting speed is too high
• Feed rate is too high
• Clearance angle is incorrect
• Cooling ineffective
• Point angle is not correct
Overheated drills

38. Feed rate is too much
Drill cutting edges are not sharp
Cooling is ineffecticve
Rough Holes

39. The cutting edges are not equal and
the point angle is not in the center of the
drill.
Unequal flow of chips

40. • Cutting speed is too high
• Feed rate is too high
• Work is not held rigidly
• Drill is not held correctly
• Drill is not sharp
• Point angle is incorrect
• Cooling is insufficient
• Flutes are clogged with chips.
Broken drill or split web

41. The combined operation of drilling and
countersinking with one tool is known as a
combination drill or center drill.
To prevent a drill from wandering off the
center, it is always a good practice to first
spot the center punch mark by center
drilling.
Centre drilling

42. The other purpose of center drilling is for
supporting the lengthy work piece by the lathe
center for lathe operations.
Jobs involving precision turning/ grinding will
be supported between the centers.

43. A center drill is made of high-speed steel and
it is cylindrical in shape.
At both the ends it has a plain drill and
countersink as integral parts.
The center drill is hardened and ground. It is
available in standard sizes
Centre drills

44. Indian Standard classifies center drills into
three types, Type A, Type B and Type R.
The difference lies in the formation of the
countersink by each type.
Classification as per Indian standard

45. Type 'A' center drill is used to produce center
holes with the plain drilled portion and
countersink.
It is designated as center drill A. 1.6 x 4.0 IS.-
6708 which means that the center drill is of Type
'A' with the plain drill portion having a diameter
of 1.6 mm and shank diameter of 4 mm.
Use and specification

46. Centre drilling can be done by a
• Drilling machine
• Lathe
• Centering machine.
The selection of a particular method of
centering depends on the size and shape of the
component.
Method of center drilling

47. A drill chuck is used to hold the center drill.
Sometimes special holders/collets are also
used.
In mass production, the raw material ends
are centered using a center drilling machine.

48. A straight or taper shank twist drill may be
used to drill a hole to sufficient depth.
Then the countersinking is done using a
60° countersink drill.
Centering in two operations

49. On a lathe, it may be done with the help
of a lathe tool, swivelling the compound slide
through 30° and turn the tapered portion In
lathe work, the size of the centre hole
depends upon the diameter of the work piece.

51. The principal types of drilling machines are
 The Portable drilling machine
 The sensitive bench drilling machine
 The pillar drilling machine
 The column drilling machine and
 The radial arm drilling machine. (Radial Drilling
Machine)
 The Gang drilling machine
 The Multi spindle drilling machine

52. Portable hand drills of different types are used
for certain jobs which cannot be handled on
stationary drilling machines.
Drilling machine (Portable type)

53. There are two types of portable drilling
machines, power operated and hand operated.
• Power operated drilling machines
• Electric hand drill (light duty)
Types

54. These are available in different forms.
The electric hand drill has a small electrical
motor for driving the drill.
On the end of the spindle, a drill chuck is
mounted.
Electric hand drills used for light duty will
have, usually, a single speed

55. This drill has an additional feature; the drill
speed can be varied through a system of
gears. This is particularly useful for drilling
larger diameter holes
Electric hand drill (Heavy Duty)

56. This type of drill is operated by compressed air.
An air driven motor is housed in the casing,
and a handle is fitted along with an air pipe to
operate the drill conveniently.
This drill is used where electrically operated
drills are prohibited i.e. explosives factories,
petroleum refineries etc.

57. Different types of hand operated drilling
machines are shown below.
They are used in structural fabrication, sheet
metal and carpentry, particularly where
electricity or pneumatic supply is not available.
Hand operated drilling machines

58. The ratchet drilling machine is commonly used
in structural fabrication.
Square head, taper shank drills are used on
these machines.
The bevel gear type drilling machine is used for
drilling small diameter holes up to 6 mm.

59. The breast drilling machine is used for drilling
holes of larger diameter as more pressure can
be exerted.
Drills between 6 mm to 12 mm can be used on
these machines.

60. The simplest type of
sensitive drilling
machines is shown in
the figure with its
various parts marked.
This is used for light
duty work.
Sensitive bench drilling machine

61. This machine is capadle of drilling holes
upto 12.5 mm diameter.
The drills are fitted in the chuck or directly
in the tappered hole of the machine
spindle.

62. For normal drilling, the work- surface is
kept horizontal. If the holes are to be drilled
at an angle, the table can be tilted.
Different spindle speeds are achieved by
changing the belt position in the stepped
pulley.

63. This is an enlarged version of the sensitive
bench drilling machine.
These drilling machines are mounted on the
floor and driven by more powerful electric
motors.
They are used for heavy duty work. Pillar
drilling machines are available in different
sizes.
Pillar drilling machine

65. Radial drilling machines are used to drill
• Large diameter holes
• Multiple holes in one setting of the work
• Heavy and large workpieces.
Radial Drilling machine

67. The radial drilling machine has a radial arm
on which the spindle head is mounted
The spindle head can be moved along the
radial arm and can be locked in any position.
The arm is supported by a pillar (column).
It can be rotated about with the pillar as
centre.
Features

68. Therefore, the drill spindle can cover the
entire working surface of the table. The arm
can be lifted or lowered.
The motor mounted on the spindle head
rotates the spindle.
The variable-speed gearbox provides a large
range of r.p.m.

69. The spindle can be rotated in both clockwise
and anticlockwise directions.
Angular holes can be drilled on machines
having tilting tables. A coolant tank is
mounted on the base.

70. • Ensure that the spindle-head and the
arms are locked properly to avoid
vibration.
• The work piece and the drill should be
rigidly held.
• Bring back the spindle head nearer to
the pillar after use.
• Switch off power when not in use.
Hints

71. • Use the drill drift for removing the drills,
chucks or sockets.
• Use a minimum number of sockets and
sleeves to make for the spindle box size.
• Clean and oil the machine after use.
• Stop the machine to remove the swarf.
• Use a brush to clean the chips and
swarf.

72. • It consists of a large base supporting
a long table. The top of the table is
designed in such a way that several
units may be mounted on it.
• Each spindle is driven by its individual
directly connected motor.
Gang drilling machine

73. • The table has a groove
around the outside for
the return of the cutting
lubricant, and may
have T-slots on its
surface for ease in
clamping the work to
the table.

74. • This type of machine is generally
preferred when the work is to be
moved from spindle to spindle for
successive operations.
• Gang of four drilling machines Each
machine is fitted with a different
cutting tool. As the work moves from
position to position a different
operation is performed

75. • The multiple spindle head drilling machine
may have any number of spindles - from 4 to
48 or more, all driven from the one-spindle
drive gear in one head.
Multiple spindle head drilling machine

76. • The multiple spindle head drilling machine is
specially designed for mass production
operations such as drilling, reaming or
tapping many holes at one time in a specific
unit of work such as an automobile engine
block.

77. • There may be two or more drill heads on
one machine, each with many spindles.
This is necessary when holes are drilled
from more than one direction - for example,
on the top side, and the end of a piece of
work.
• Production units of this type are seldom
used in a tool room that usually does highly
skilled work

79. 1. Drilling
2. Reaming
3. Boring
4. Counter boring
5. Countersinking
6. Spot Facing
7. Tapping
8. Lapping
9. Grinding
10. Trepanning

81. Drilling is the operations, of producing a
cylindrical hole by removing metal by the
rotating edge of a cutting tool called the drill.
The drilling is one of the simplest methods of
producing a hole.
Drilling

82. Drilling Operation

83. Before drilling the centre of the hole is located
on the workpiece by drawing two tines at right
angles to each other and then a centre punch
is used to produce an in dentation., at the
centre.
The drill point is pressed at this centre point to
produce the required hole. Drilling does not
produce an accurate hole in a workpiece and
the hole location is not perfect.

84. The internal surface of the hole so generated
by drilling becomes rough and the hole is
always slightly oversize than the drill used due
to the vibration' of the spindle and the drill.
A 12 mm drill may produce a hole as much as
6.125 mm oversize and a 22 mm drill may
produce one as much as 0.5 mm oversize.

85. Reaming is an accurate way of sizing and
finishing a hole which has been previously
drilled. In order to finish a hole and to bring it to
the accurate size, the hole is drilled slightly
undersize.
The speed of the spindle is made half that of
drilling and automatic feed may be employed.
Reaming

87. The tool used for reaming is known as the
reamer which has multiple cutting edges.
Reamer cannot originate a hole.
It simply follows the path which has been
previously drilled and removes a very small
amount of metal.

88. For this reason a reamer cannot correct a hole
location.
The material removed by this process is
around 0.375 mm and for accurate work this
should not exceed 0.125 mm.

89. Boring is performed in a drilling machine
for reasons stated below
1. To enlarge & hole by means of an
adjustable cutting tool with only one cutting
edge. This is necessary where suitable sized
drill is not available or where hole diameter is
so large that it cannot he ordinarily drilled.
Boring

91. 2. To finish a hole accurately and to bring it
to the required size
3. To machine the internal surface of a
hole already produced in casting.
4. To correct out of roundness of the hole.
5. To correct the location of the hole as the
boring tool follows an independent path with
respect to the hole.

92. The cutter is then held in a boring bar which
has a taper shank to fit into the spindle socket.
For perfect finishing a hole, the job is drilled
slightly undersize.
In precision machines, the accuracy is as
high as + or - 0.00125 mm.
It is a slow process than reaming and
requires several passes of the tool.

93. Counter boring is the operation of enlarging
the end of a hole cylindrically.
The enlarged hole forms a square shoulder
with the original hole. This is necessary in
some cases to accommodate the heads of
bolts, studs and pins.
Counter boring

95. The tool used for Counter boring is called a
counter bore. The counter bores are made
with straight or tapered shank to fit in the drill
spindle, the cutting edges may have straight or
spiral teeth. The tool is guided by a pilot which
extends beyond the end of the cutting edges.

96. The pilot tits into the small diameter hole
having running clearance and maintains the
alignment of the tool. These pilots may be
interchanged for enlarging
different sizes of holes. Counter boring can
give an accuracy of about +or- 0.050 mm. The
cutting speed for counter boring is 25 % less
than that of drilling operation.

97. Countersinking is the operation of making a
cone-shaped enlargement of the end of a hole
to provide a recess for a flat head screw or
countersunk rivet fitted into the hole.
The tool used for countersinking is called a
countersink. Standard countersinks have 60 ,
82 Or 90 degrees included angle
Countersinking

99. And the cutting edges of the tool are formed
at the conical surface.
The cutting speed in countersinking is 25 %
less than that of drilling.

100. Spot facing is the operation of smoothing
and squaring the surface around a hole for the
seat for a nut or the head of a screw.
A counter bore or a special spot facing tool
may be employed for this purpose.
Spot facing

102. Tapping is the operation of cutting internal
threads by means of a cutting tool called a tap.
Tapping in a drilling machine may be
performed by hand or by machine. A tap
maybe considered as a bolt with accurate
threads cut on it.
Tapping

103. The threads act as cutting, edges which are
hardened and ground. When the tap is
screwed into the hole it removes metal and
cuts internal threads which will fit into external
threads of the same size.

105. Lapping is the operation of sizing and
finishing a small diameter hole already
hardened by removing a very small amount of
material by using a lap.
There are many kinds of lapping tools. The
copper head laps are commonly used. The
lap fits in the hole and is moved up and down
when it revolves.
Lapping

107. Trepanning is the operation of producing a
hole by removing metal along the circumference
of a hollow cutting tool.
Trepanning operation is performed for
producing large holes. Fewer chips are removed
and much of the material is saved while the hole
is produced.
Trepanning

109. The tool may be operated at higher speeds as
the variation in diameter of the tool is limited by
the narrow cutting edge.
The tool resembles a hollow tube having
cutting edges at one end and a solid shank at
the other to fit into the drill spindle.
This is one of the efficient methods of
producing a hole.

112. For drilling holes on materials, the drills are to
be held accurately and rigidly on the machines.
The common drill-holding devices are drill
chucks and sleeves and sockets.

113. Straight shank drills are held in drill chucks.
For fixing and removing drills, the chucks are
provided either with a pinion and key or a
knurled ring.
The drill chucks are held on the machine
spindle by means of an arbor fitted on the drill
chuck.
Drill Chuck

115. Taper shank drills have a Morse taper.
Sleeves and sockets are made with the
same taper so that the taper shank of the drill,
when engaged, will give a good wedging
action.
Due to this reason morse tapers are called
self-holding tapers.
Taper sleeves and sockets

117. Drills are provided with five different sizes of
Morse tapers, and are numbered from MT 1 to
MT 5.
In order to make up the difference in sizes
between the shanks of the drills and the type of
machine spindles, sleeves of different sizes are
used.

118. When the drill taper shank is bigger than the
machine spindle, taper sockets are used.
While fixing the drill in a socket or sleeve,
the tang portion should align in the slot.
This will facilitate the removal of drill or
sleeve from the machine spindle. Use a drift to
remove drills and sockets from the machine
spindle.

121. Workpieces to be drilled should be properly
held or clamped to- prevent from rotating along
with the drill.
Improperly secured work is not only a danger
to the operator but can also cause inaccurate
work, and breakage to the drill.
Various devices are used to ensure proper
holding.

122. Most of the drilling work can be held in a
machine vice. Ensure that the drill does not
drill through the vice after it has passed
through the work.
Machine Vice

123. For this purpose, the work can be lifted up
and secured on parallel blocks providing a
gap between the work and the bottom of the
vice.
Work pieces that are not accurate may be
supported by wooden pieces.

124. Drilling machine tables are provided with
T-slots for fitting bolt heads. Using clamps and
bolts, the Workpieces can be held very rigidly.
While using this method, the packing
should be, as far as possible, of the same
height as the work, and the bolt nearer to the
work.
Clamps and bolts

126. For a drill to give a satisfactory performance,
it must operate at the correct cutting speed and
feed.Cutting speed is the speed at which the
cutting edge passes over the material while
cutting, and is expressed in meters per
minute.Cutting speed is also sometimes stated
as surface speed or peripheral speed.
Cutting speed and RPM

127. The selection of the recommended cutting
speed for drilling depends on the materials to
be drilled, and the tool material.
Tool manufacturers usually provide a table
of cutting speeds required for different
materials.

128. The recommended cutting speeds for
different materials are given in the table. Based
on the cutting speed recommended, the r.p.m.
at which a drill has to be driven, is determined.

130. Materials being drilled for
HSS
Cutting speed
(m/min)
Aluminum 70-100
Brass 35-50
Bronze (phosphor) 20-35
Cast iron (grey) 25-40
Copper 35-45
Steel (medium Carbon/mild.
Steel)
20-30
Steel (alloy, high tensile) 5-8
Thermosetting . plastic (low
speed due to abrasive
properties)
20-30

131. Calculating RPM

132. Feed is the distance (X) a drill advances
into the work in one complete rotation
Feed is expressed in hundredths of a
millimeter.
Example - 0.040 mm
Feed in Drilling

133. The rate of feed is dependent upon a
number of factors.
• Finish required
• Type of drill (drill material)
• Material to be drilled

134. Factors like rigidity of the machine, holding
of the work-piece and the drill, will also have
to be considered while determining the feed
rate.
If these are not to the required standard,
the feed rate will have to be decreased.

135. It is not possible to
suggest a particular feed
rate taking all the factors
into account.
The table for the feed
rate given here is based on
the average feed values
suggested by the different
manufacturers of drills.

136. Drill diameter
(mm) H.S.S.
Rate of feed
(mm/rev)
1.0-2.5 0.040-0.060
2.6-4.5 0.050-0.100
4.6-6.0 0.075 -0.150
6.1 -9.0 0.100-0.200
9.1 -12.0 0.150-0.250
12.1 -15.1 0.200 - 0.300
15.1 - 18.0 0.230 - 0.330
18.1 -21.0 0.260 -0.360
21.1 -25.0 0.280 - 0.380

137. Too coarse a feed may result in damage to
the cutting edges or breakage of the drill.
Too slow a rate of feed will not bring
improvement in surface finish but may cause
excessive wear of the tool point, and lead to
chattering of the drill.

139. T-Drilling time in min
L-Approach length in mm
l-Work piece length in mm
A-Lip Angle in degree
N-Feed mm/min