Assignment No: Roll No:

Name of Assignment: Drilling

Q1. Explain twist drill nomenclature with neat diagram.

The twist drill nomenclature has been described below:
1. Axis: It is the longitudinal center-line of
the drill.
2. Diameter: Largest diameter measured
across the top of the lands behind the
point.
3. Back Taper: The diameter reduces
slightly toward the shank end of the drill;
this is known as “back taper”. Back taper
provides clearance between the drill and
work-piece preventing friction and heat.
4. Body: It is the part of the drill from its
extreme point to the commencement of
the neck.
5. Neck: The portion with reduced diameter
in between body and shank.
6. Shank: It is the part of the drill by which it is held and driven. The shank may be straight
or taper.
7. Tang: The flattened end of the taper shank is known as tang.
8. Point: It is the conical sharpened end of the drill.
9. Flank: Surface of drill which extends behind the lip to flute.
10. Flutes: The grooves in the body of the drill are known as flutes.
11. Flute Length: The length of flute measured from the drill point to the end of the flute run
out. Flute length determines the maximum depth of drilling.
12. Margins: The cylindrical portion of the land that is not cut away to provide clearance.
13. Helix Angle: Angle formed between a line drawn parallel to the axis of the drill and the edge
of the land. (30° or 45°)
14. Point angle: This is the angle included between the two lips projected upon a plane parallel
to the drill axis and parallel to the two cutting lips (118°).
15. Chisel Edge: It is the point where two cutting lips meet at extreme tip.
16. Chisel Edge Angle: Angle between chisel edge and cutting lip measured plane normal to
axis.

Q2. Explain drilling, boring, reaming, counterboring, countersinking and spot facing
operations.
A. Drilling:
a. Drilling is the operation of producing a cylindrical hole by removing metal by the rotating
metal by the rotating edge of a cutting tool called drill.
b. The drilling is one of the simplest methods of producing a hole. Before drilling the center of
the hole is located on the workpiece by drawing two lines at right angles to each other and then
the center punch is used to produce an indentation at the center the drill point is pressed at
this center point to produce the required hole.
c. Drilling does not produce an accurate hole on the workpiece and the hole so generated by
drilling becomes rough and the hole is always slightly oversize than the drill used due to the
vibrations of the spindle and the drill.

B. Boring:
a. Occasionally a straight and smooth hole is needed which is too large or odd sized for drills or
reamers. A boring tool can be inserted into the drilling machine and bore any size hole into
which the tool holder will fit.
b. A boring bar with a tool bit installed is used for boring on the larger drilling machines. To
more accurately, the setup must be rigid, machine must be sturdy, and power feed must be
used. Boring is not recommended for hand-feed drilling machines.
c. Hand feed is not smooth enough for boring and can be dangerous. The tool bit could catch
the workpiece and throw it back at the operator. First, secure the work and drill a hole for the
boring bar. Then, insert the boring bar without changing the setup.
d. Use a dial indicator to set the size of bored hole desired by adjusting the tool bit in the boring
tool holder; then, set the machine speed and feed. The speed is set at the speed recommended
for drilling a hole of the same size. Feed should be light, such as 0.005 to 0.010 inch per
revolution. Start the machine and take a light cut.
e. Check the size of the hole and make necessary adjustments. Continue boring with a rougher
cut, followed by a smoother finishing cut. When finished, check the hole with an internal
measuring device before changing the setup in case any additional cuts are required.

C. Reaming:
a. Reaming a drilled hole is another operation that can be performed on a drilling machine. It is
difficult, if not impossible, to drill a hole to an exact standard diameter. When great accuracy is
required, the holes are first drilled slightly undersized and then reamed to size.
b. Reaming can be done on a drilling machine by using a hand reamer or using a machine
reamer. When you must drill and ream a hole, it is best if the setup is not changed.
c. For example, drill the hole (slightly undersized) and then ream the hole before moving to
another hole. This method will ensure that the reamer is accurately aligned over the hole.
d. If a previously drilled hole must be reamed, it must be accurately realigned under the
machine spindle. Most hand and machine reamers have a slight chamfer at the tip to aid in
alignment and starting

D. Counter-boring:
a. When counterboring, mount the tool into the drill chuck and set the depth stop 'mechanism
for the required depth of shoulder cut. Set the speed to approximately one-half that for the
same size of twist drill. Compute for the actual cutter size and not the shank size when figuring
speed. Mount the workpiece firmly to the table or vise.
b. Align the workpiece on the center axis of the counterbore by fitting the pilot into the drilled
hole. The pilot should fit with a sliding motion inside the hole. If the pilot fits too tightly, then
the pilot could be broken off when attempting to counterbore. If the pilot fits too loosely, the
tool could wander inside the hole, causing chatter marks and making the hole out of round.
c. Feeds for counterboring are generally 0.002 to 0.005 inch per revolution, but the condition of
the tool and the type of metal will affect the cutting operation. Slow the speed and feed if
needed. The pilot must be lubricated with lubricating oil during counterboring to prevent the
pilot seizing into the work. Use an appropriate cutting fluid if the material being cut requires it.
d. Use hand feed to start and accomplish counterboring operations. Power feed counterboring
is used mainly for production shops.

E. Countersinking:
a. Countersinking is the tapering or beveling of the end of a hole with a conical cutter called a
machine countersink. Often a hole is slightly countersunk to guide pins which are to be driven
into the workpiece; but more commonly, countersinking is used to form recesses for flathead
screws and is similar to counter-boring.

F. Spot facing:
a. Spot facing is basically the same as counterboring, using the same tool, speed, feed, and
lubricant. The operation of spot facing is slightly different in that the spot facing is usually done
above a surface or on a curved surface.
b. Rough surfaces, castings, and curved surfaces are not at right angles the cutting tool causing
great strain on the pilot and counterbore which can lead to broken tools. Care must be taken
when starting the spot facing cut to avoid too much feed.
c. If the tool grabs the workpiece because of too much feed, the cutter may break or the
workpiece may be damaged. Ensure that the work is securely mounted and that all backlash is
removed from drilling machine spindle.

Q3. Explain various work holding and tool holding devices used on drilling machine.
Before performing any operation in the drilling machine, it is absolutely necessary to secure the
work firmly on the drilling machine table. The work should never be held by hand, because the
drill while revolving exerts so much of torque on the workpiece that it starts revolving along
with the tool and may cause injuries to the operator. The devices commonly used for holding
the work in a drilling machine are:
A. T-bolts and clamps:
a. One of the most common methods of holding the work directly on the drilling machine table
is by means of T-bolt and clamps. Drilling machine table are provided with T-slots into which T-
bolts may be fitted.
b. The diameter of T-bolts usually ranges from 15 to 20 mm. The clamps or straps are made of
mild steel flats 12 to 20 mm thick and 45 to 70 mm wide. Types of clamps are:
1. Plain slot clamp. 4. Finger clamp.
2. Goose neck clamp. 5. Adjustable step clamp.
3. U-clamp.
B. Drill press vice:
The drill press vice is one of the most common methods of holding small and regular shape
workpieces. The work is clamped in a vice between a fixed jaw and a movable jaw. Extra slip
jaw is supplied for holding cylindrical or hexagonal bars. The screw of the vice rotates in a fixed
nut in the movable jaw. The screw of the vice may be square or acme threaded.

C. Step block:
a. The step blocks are used in conjunction with T-bolts and clamps or for holding the work
directly on the table. The step block provides support for the other and of the clamp.
b. The different steps of the step block are used for leveling the clamp will handling workpieces
of different height. The step blocks are made mild steel.

D. V-blocks:
The v-blocks are used for holding round workpieces. The work may be supported on two or
three blocks and clamp CD against them by straps and bolts. V-blocks are accurately machined
cast iron or steel blocks.

E. Angle plates:
The angle plates are usually made of cast iron having two faces at right angles to each other’s.
The faces are accurately finished and are provided with holes and slots for clamping the work
on one of its face will the other face rests open the table and is bolted to it. Angle plates are
used when it is necessary to drill a hole parallel to another surface.

F. Drill jigs:
The drill jigs are used for holding the work in a mass production process. A jig can hold the work
securely, locate the work and guide the tools at any desired position. The work may be clamped
and unclamped quickly. Jigs are specially designed for each type of work where quantity
production is desired. Holes may be drilled at the same relative positions on each of the
identical workpieces without marking the work individually. The work is clamped below the jig
and the holes are located. The drill is guided by the bushing, and when the work is completed
the second work is clamped below the jig and the process is repeated.

The revolving spindle of a drilling machine can hold different cutting tools for different
operations. The different used for holding tools in a drill spindle are:
A. Directly holding the tool:
a. All general-purpose drilling machines have the spindle bored out to a standard taper to
receive the taper shank of the tool. The taper used in a drill spindle is usually Morse standard
which is Drill inserted Slots for inserting drifts, Drill spindle Sleeve, Drill taper approximately
1:20.
b. While fitting the tool the shank is forced into the tapered
hole and the tool is gripped by friction. The tool may be
rotated with the spindle by friction between the tapered
surface and the spindle; but to ensure a positive drive the tang
or tongue of the tool fits into a slot at the end of the taper
hole. The tool may be removed by pressing a tapered wedge
known as the drift into the slotted hole of the spindle. A drill
fitted directly into the spindle through a sleeve.
c. Noted that sleeve used in drill spindle should not be affected
while the drift is pushed to take out the drill bit. Usually a
mallet should be used instead of a hammer. The operator
must be ensuring that Fig.5.18 shows a drift or key. It can be the
tool is not dropped while removing it. The taper should be
standardized to the Morse standard taper and non-standard taping should not be allowed for
drill spindle sleeve. Unmatched drill spindle and sleeve may cause inconvenience during
machine running.

B. Sleeve:
a. The drill spindle is suitable for holding only one size of shank. If the taper shank of the tool is
smaller than the taper in the spindle hole, a taper sleeve is used. The outside taper of the
sleeve conforms to the drill spindle taper and the inside taper holds the shanks of smaller size
tools or smaller sleeves. The sleeve fits into the taper hole of the spindle and holds tool shanks
of smaller sizes in the tapered hole.
b. The sleeve has a flattened end or tang which fits into the slot of the spindle. The tang of the
tool fits into a slot provided at the end of the taper hole of the sleeve. The sleeve with the tool
may be removed by forcing a drift within the slot of the spindle and the tool may be separated
from the sleeve by the similar process.
c. Different sizes of tool shanks may be held in the spindle by using different sizes of sleeve. The
taper on the outer surface does not change but that on the inner surface varies with the
different sizes of the tool shanks.

C. Socket:
a. When the tapered tool shank is larger than the spindle taper drill sockets are used to hold
the tool. Drill sockets are much longer in size than the drill sleeves.
b. A socket consists of a solid shank attached to the end of a cylindrical body. The taper shank
of the socket conforms to the taper of the drill spindle and fits into it.
c. The body of the socket has a tapered hole larger than the drill spindle taper into which the
taper shank of any tool may be fitted. The tang of the socket fits into the slot of the spindle and
the tang of the tool fits into the slot of the socket.
D. Drill chucks:
a. The chucks are especially intended for holding smaller size drills or any other tools. A sleeve
or socket can hold one size of tool shank only but a chuck may be used to hold different sizes of
tool shanks within a certain limit.
b. Drill chucks have tapered shanks which are fitted into the drilling machine spindle. Different
types of drill chucks are manufactured for different purposes. The most common types of
chucks are:
1. Quick change chuck.
2. Three-jaw self-centering chuck.

Q4. Give the classification of drilling machine.

Different types of drilling machines are as follows:
1. Portable drilling machine.
2. Sensitive drilling machine.
i) Bench mounting.
ii) Flour mounting.
3. Upright drilling machine.
i) Round column section.
ii) Box column section.
4. Radial drilling machine.
i) Plain.
ii) Semi universal.
iii) Universal.
5. Gang drilling machine.
6. Multiple spindle drilling machine.
7. Automatic drilling machine.
8. Deep hole drilling machine.
i) Vertical.
ii) Horizontal.

Q5. Explain radial drilling machine with neat sketch.

a. The radial drilling machine is intended for drilling medium to large and heavy workpieces.
The machine consists of a heavy, round, vertical column mounted on a large base. The column
supports a radial arm which can be raised and lowered to accommodate workpieces of
different heights. The arm may be swung around to any position over the work bed.
b. The drill head containing mechanism for rotating and feeding the drill is united on a radial
arm and can be moved horizontally on the guide-ways clamped at any desired position. These
three movements in a radial ng machine when combined together permit the drill to be located
at desired point on a large workpiece for drilling the hole.
c. When several les are drilled on a large workpiece, the position of the arm and the drill Nd is
altered so that the drill spindle may be moved from one position to work be other after drilling
the hole without altering the setting versatility of the machine allows it to work on large
workpieces. They may be mounted on the table or when the work is very large it may place on
the floor or in a pit.
d. Plain radial drilling machine: In a plain radial drilling machine provisions are made for vertical
adjustment of the arm, horizontal movement of the drill head along the arm, and circular
movement of the arm in horizontal plane about the vertical column.
e. Semi Universal machine: In a semi universal machine, in addition to the above three
movements, the drill head can be swung about a horizontal axis perpendicular to the am. This
fourth movement of the drill had permits drilling hole at an angle to the horizontal plane other
than the normal position.
f. Universal machine: In a universal machine, in addition to the above four movements, the arm
holding the drill head may be rotated on a horizontal axis. All these five movements in a
universal machine enable it to drill on a workpiece at any angle.