Drilling is a cutting process that uses
a drill bit to cut or enlarge a hole of
circular cross-section in solid
materials. The drill bit is a rotary
. The bit is pressed against the work
piece and rotated at rates from
hundreds to thousands of revolutions
It is estimated that 75 % of all metal
cutting material removed ,comes from
Working Principle :-
The rotating edge of the drill
exerts a large force on the
work piece and the hole is
The removal of metal in a
drilling operation is by
shearing and extrusion.
The chips must exit out of the hole created by
Chip exit can cause problems when chips are
large and/or continuous.
The drill can wander upon entrance and for
For deep holes in large work pieces, coolant
may need to be delivered through the drill
shaft to the cutting front.
Sensitive Drilling machine :-
It is a small machine used for drilling small holes
in light jobs. In this drilling machine, work piece
is mounted on the table and drill is fed into the
work by purely hand control.
High rotating speed of the drill and hand feed
are the major features of sensitive drilling
.As the operator senses the drilling action in the
work piece, at any instant, it is called sensitive
A sensitive drilling machine consists of a
Drills of diameter from 1.5 to 15.5 mm can be
rotated in the spindle of sensitive drilling machine.
Upright Drilling machine:-
The upright drilling machine is larger and
heavier than a sensitive drilling machine
It is designed for handling medium sized
work piece and is supplied with power feed
this machine a large number of spindle
speeds and feeds may be available for
drilling different types of work
Upright drilling machines are available in
various sizes and with various drilling
capacities (ranging up to 75 mm diameter
Radial Drilling machine :-
A Radial drilling machine consists of a
heavy, round vertical column supporting a
horizontal arm that carries the drill head.
The table of radial drilling machine may
also be rotated through 360 deg. The
maximum size of hole that the machine can
drill is not more than 50 mm.
Powerful drive motors are geared directly
into the head of the machine and a wide
range of power feeds are available as well
as sensitive and geared manual feeds.
It is used primarily for drilling medium to
large and heavy work pieces.
Gang Type Drilling machine :-
In gang drilling machine, a number of
single spindle drilling machine
columns are placed side by side on a
common base and have a common
A series of operation may be
performed on the job by shifting the
work from one position to the other on
a number (2 to 6) of spindles with drills
(of same or different size) in a row are
made to produce number of holes
progressively or simultaneously
5.Multi spindle drilling machine:-
The multiple-spindle drilling machine
is used to drill a number of holes in a
job simultaneously and to reproduce
the same pattern of holes in a number
of identical pieces in a mass
The entire drilling head works
repeatedly using the same jig for
batch or lot production of a particular
Geometry parts of twisted drill :-
Twist drill geometry and its nomenclature are
shown above. twist drill has three
(i) Drill point or dead center
Drill axis is the longitudinal line .
Drill point is the sharpened end of the drill body
consisting of all that part which is shaped to
produce lips, faces and chisel edge.
Lip or cutting edge is the edge formed by the
intersection of the flank and face
Lip length is the minimum distance between the
outer corner and the chisel-edge corner of the
Parts of twisted drill :-
Face is that portion of the flute surface
adjacent to the lip on which the chip impinges
as it is cut from the work.
Chisel edge is the edge formed by the
intersection of the flanks.
Flank is that surface on a drill point which
extends behind the lip to the following flute.
Flutes are the grooves in the body of the drill,
which provide lips, allow the removal ofchips,
and permit cutting fluid to reach the lips.
Flute length is the axial length from the
extreme end of the point to the termination of
the flutes at the shank end of the body.
Parts of twisted drill :-
Body is that portion of the drill nomenclature, which extends
from the extreme cutting end to the beginning of the shank.
Shank is that portion of the drill by which it is held and driven,
Heel is the edge formed by the intersection of the flute surface
and the body clearance.
Body clearance is that portion of the body surface reduced in
diameter to provide diametric clearance.
Core or web is the central portion of the drill situated between
the roots of the flutesand extending from the point end towards
the shank; the point end of the core forms the
Lands are the cylindrically ground surfaces on the leading
edges of the drill flutes..
Drilling Operations :-
Drilling :-operation of making a circular hole
by removing a volume of metal from the job
by a rotating cutting tool called drill.
Boring :-Process of enlarging a hole.
Reaming :-Operation of finishing a drilled
Counter boring :-Operation of boring a
second hole ,larger in diameter than the
first, but concentric with it.
Counter sinking :-Operation of producing an
angular surface at the end of a hole.
Spot facing:-Operation of machining a flat
,circular surface around a hole to provide a
seat for a bolthead, nut or washer.
Boring is a process of producing
circular internal profiles on a hole
made by drilling or another process.
It uses single point cutting tool called a
The boring bar can be rotated, or the
work part can be rotated.
Machine tools which rotate the boring
bar against a stationary work piece
are called boring machines (also
Boring Machines :-
1.Horizontal boring machine :-
A horizontal boring machine or
horizontal boring mill is a machine tool
which bores holes in a horizontal
There are three main types — table,
planer and floor.
The table type is the most common
and, as it is the most versatile, it is
also known as the universal type.
Used for drilling ,boring, and milling
Vertical boring machine :-
A large type of boring machine in
which a rotating work piece is
fastened to a horizontal table, which
resembles a four-jaw independent
chuck with extra radial T slots, and the
tool has a traverse motion.
Cutting tools are stationary except for
Boring defects :-
1. Poor surface finish
Cutting speed too low, feed rate too
,blunt tool ,
1. Incorrect front clearance ,lack of
rigidity in boring
Improperly applied coolant ,cutting
speed too low
4.Excessive tool wear :-
The process of enlarging the hole is
called reaming. There are many different
types of reamer and they may be
designed for use as a hand tool or in a
machine tool, such as a milling machine
or drill press.
1.Straight reamer :-
A straight reamer is used to make only a
minor enlargement to a hole. The entry
end of the reamer will have a slight taper,
the length of which will depend on its type
2.Hand reamer :-A hand reamer has a
longer taper or lead in at the front than a
machine reamer. This is to compensate for
the difficulty of starting a hole by hand
power alone. It also allows the reamer to
start straight and reduce the risk of
breakage. The flutes may be straight or
3.Machine reamer:-machine reamer only
has a very slight lead in. Because the
reamer and work piece are pre-aligned by
the machine there is no risk of it wandering
4.Shell reamer:-Shell reamers are
designed for reaming bearing and
other similar items. They are fluted
almost their whole length.
5. Taper reamer :-A precision tapered
reamer is used to make a tapered hole
to later receive a tapered pin.