2. Review Topic
2.1 Differentiate between the drilling machine and drill
bit
2.1.1 Sketch and name parts of a drill bit (twist drill)
2.1.2 Explain how drill sizes are stated and determined
2.1.3 Explain steps of marking out before drilling
2.1.4 Explain method of holding a drill bit
2.1.5 Calculate the spindle speed revolution (rpm) and
the feed rate including factors that influence the
selection of the cutting speed
2.1.6 State the types of coolants, function and advantages
2.1.7 Prepare the Standard Operating Procedure drilling
16. Parts of Twist Drill
1. Point: The point is the cone shaped end and it does the cutting. It
consists of the following:
(A) Dead centre: It is the sharp edge at the extreme tip of the
drill. This should always be the exact centre
of the drill.
(B) Lips :These are the cutting edges of the drill.
(C) Heel : It is the portion of the point back from the
cutting edge.
2. Shank :
It is the portion of the drill by which it is clamped in the spindle. The
shank may be either straight or tapered. Straight shank drills are used
with a chuck. Tapered shank drills have self-holding tapes that fit
directly into the drill press spindle. On the taper shank is the another
term is used which is called tang. This fits into a slot in the spindles
sleeve.
17. 3. Body :
It is the portion between the point and the shank. The body
consists of the following parts:
(A) Flutes :
Two or more spiral grooves that run the length of the drill body are called
flutes. The flutes do four thing.
Help from the cutting edge of the drill point.
Curl the chip tightly for easier removal.
From channels through which chips can escape from the hole
being drilled.
Allow the coolant and lubricant to get down to the cutting edge.
(B) Margin
It is the narrow strip extending back the entire length of the flute. It is the
full diameter of the drill.
(C) Body Clearance:
It is the part of the drill body that has been reduced in order to cut down
friction between the drill and the wall of the hole
18. Angles of A Drill
Rake or helix angle: angle between a plane containing the drill
axis and leading edge of the land. It can have +ve, -ve or zero
right hand flute have +ve, left hand flute have –ve, parallel have
zero. Angle varies 0-48 (16-32 is generally used). Higher angle for
softer materials and lower for harder .
Point angle (cutting angle) : angle between two opposite lips of
the drill ( 80-140) ,118 for large variety of materials, smaller angle
for brittle materials, larger for harder materials
Lip clearance angle: angle between flank and plane normal to
drill axis (8-15) ,12 is most common
Chisel edge angle: angle formed between the cutting lip and
chisel edge (120-135) greater this angle larger will be clearance.
23. According to type of shank they carry
Parallel shank
Tapper shank
According to type of flutes
flat drill
twist drill
According to length
short series: 0.2mm-16mm
stub series: 0.5mm-40mm
long series: 1.5mm-26mm
24. According to application:
Core drill: carry 3 parallel flutes ,used for enlarging
drilled holes
Drill for long hole drilling: heavy duty drill and
larger helix angle
Centre drill:
Masonry drill :4mm-20mm, cutting anle:115used
for drilling centre holes
According to the tool material:
High speed steel drill
Carbide tipped drill
25. Steps Of Marking Out Before Drilling
1. The workpiece should be cleaned and deburred
before applying layout dye.
2. The position of the center of the hole to be drilled is
marked by scribing two or more lines which intersect
at the hole center.
3. This intersecting point is then marked lightly with a
prick punch and hammer.
4. Check to see that the punch mark is exactly at the
center of the intersection; use a magnifying glass if
necessary.
26. 5. Use a pair of dividers, set to the radius of the hole to
be drilled, to scribe a circle on the workpiece.
6. The prick punch is then used to mark small
indentations, known as “witness marks,” on the
circumference.
7. When all scribing is finished, enlarge the prick
punch mark with a center punch to aid the center
drilling process.
8. Enlarging the mark with a center punch allows the
center drill point to enter the workpiece easier and
cut smoother.
34. Various Types Of Drill Bits Such As
Centre Drill, Straight Slot Drill, Blind
Hole Drill And Flat Tipped Drill
35. Drilling And Drills
Types of drills
– Twist drill: most
common drill
– Step drill:
produces holes
of two or more
different
diameters
– Core drill: used
to make an
existing hole
bigger
37. EFFECTS TO A DRILLED HOLE IF
THE ANGLE OF THE DRILL BIT TIP IS
NOT ACCURATE
38. When both the angles and the length of the angles are
incorrect, then excessive wear is put on both the drill
and machine, which will result in poor workmanship
39. Calculate The Spindle Speed
Revolution (Rpm) And The Feed Rate
Including Factors That Influence The
Selection Of The Cutting Speed
40.
41. Feed Rate
The feed rate for drilling depends upon the
hardness of the material, the type of material the
drill is made of, and the size of the drill bit.
The feed rate that can be used is determined
mainly by the size of the chip that the drill can
withstand. As the size of the drill increases, the
feed rate of the drill also increases.
46. 1. Cutting fluids, lubricants, and coolants are used in
drilling work to lubricate the chip being formed for
easier removal, to help dissipate the high heat caused
by friction, to wash away the chips, to improve the
finish, and to permit greater cutting speeds for best
efficiency.
47. 2. In drilling work, the cutting fluid can be sprayed,
dripped, or machine pumped onto the work and
cutting tool to cool the action and provide for
maximum tool life.
3. Drilling, reaming, and tapping of various materials
can be improved by using the proper cutting fluids
4. Cutting- fluids can be produced from animal,
vegetable, or mineral oils.
48. 5. Some cutting fluids are very versatile and can be
used for any operation, while other cutting fluids are
specially designed for only one particular metal.
49.
50. State The Safety Procedures To Be
Taken While Drilling
1. Do not support the work piece by hand – use work
holding device.
2. Use brush to clean the chip
3. No adjustments while the machine is operating
4. Ensure for the cutting tools running straight before
starting the operation.
5. Never place tools on the drilling table
6. Avoid loose clothing and protect the eyes.
7. Do not leave the machine running unattended.
51. The Reason For Holding The Work
Piece Securely While Drilling
to hold the work steady for an accurate hole to be
drilled
a safe drilling operation can be accomplished
keep the workpiece above the worktable or vise surface
To keep the workpiece aligned for drilling
52. The Types Work Holding Devices
Commonly Used In A Drilling Machine
Such As Machine Vice, Machinist Vice,
V Block And Others
53.
54.
55.
56.
57.
58.
59. V-blocks
V-blocks are precision made blocks with special slots
made to anchor clamps that hold workplaces.
The V-slot of the block is designed to hold round
workplaces.
The V-block and clamp set is usually used to hold and
drill round stock.
60. Jigs
Drill jigs are devices designed for production drilling
jobs.
The workplaces are clamped into the jig so that the
holes will be drilled in the same location on each
piece.
The jig may guide the drill through a steel bushing to
locate the holes accurately.
61. Types Of Drilling Jigs:
Drilling jigs may be classified as follows:
Template jig
Plate type jig
Open type jig
Channel jig
Leaf Jig
Box type jig
62. Template Jig
This is the simplest type of jig;
It is simply a plate made to the shape and size of the
work piece; with the require number of holes made it.
It is placed on the work piece and the hole will be
made by the drill; which will be guided through the
holes in the template plate should be hardened to
avoid its frequent replacement.
This type of jig is suitable if only a few part are to be
made.
63.
64. Open Type Jig
In this jig the top of the jig is open; the work piece is
placed on the top.
