previous year ies

1. Drilling
By S K Mondal

2. Drilling
 Drilling is a operation that cuts cylindrical holes.

3. Video

4. TYPES OF DRILL PRESSES
 Vertical or pillar type
 Radial Arm type
 Gang drill
 Multi Spindle drill
 Numerical Control drill

5. Video

6. Drilling Operations

7. Chip formation
of a drill

8. Drill
 The twist drill does most of the cutting with the tip of
the bit.
•There are flutes
to carry the chips
up from the
cutting edges to
the top of the
hole where they
are cast off.

9. Drill

10. IES - 2004
Consider the following statements:
The helical flute in a twist drill provides the necessary
1. Clearance angle for the cutting edge
2. Rake angle for the cutting edge
3. Space for the chip to come out during drilling
4. Guidance for the drill to enter into the workpiece
Which of the statements given above are correct?
(a) 1 and 2 (b) 2 and 3
(c) 3 and 4 (d) 1 and 4

11. IES - 2003
The purpose of helical grooves in a twist drill is to
1. Improve the stiffness
2. Save a tool material
3. Provide space for chip removal
4. Provide rake angle for the cutting edge
Select the correct answer using the codes given below:
Codes:
(a) 1 and 2 (b) 2 and 3
(c) 3 and 4 (d) 1 and 4

12. Drill
 Axial rake angle is the angle between the face and the line
parallel to the drill axis. At the periphery of the drill, it is
equivalent to the helix angle.
 The lip clearance angle is the angle formed by the portion of
the flank adjacent to the land and a plane at right angles to
the drill axis measured at the periphery of the drill.
 Lead of the helix is the distance measured parallel to the drill
axis, between corresponding point on the leading edge of the
land in one complete revolution.

13. Drill
 Drill sizes are typically measured across the drill points with
a micrometer
 Most widely used material is High Speed Steel
 The drill blanks are made by forging and then are twisted to
provide the torsional rigidity. Then the flutes are machined
and hardened before the final grinding of the geometry.
 Deep hole drilling requires special precautions to take care of
the removal of large volume of chips.

14. GATE- 1996
The rake angle in a drill
(a) Increases from centre to periphery
(b) decreases from centre to periphery
(c) Remains constant
(d) Is irrelevant to the drilling operation

15. IES - 1997
The rake angle in a twist drill
(a) Varies from minimum near the dead centre to a
maximum value at the periphery
(b) Is maximum at the dead centre and zero at the
periphery
(c) Is constant at every point of the cutting edge
(d) Is a function of the size of the chisel edge.

16. Point Angle (2β)
 The point angle is selected to suit the hardness and brittleness of
the material being drilled.
 Harder materials have higher point angles, soft materials have
lower point angles.
 An increase in the drill point angle leads to an increase in the
thrust force and a decrease in the torque due to increase of the
orthogonal rake angle.
 This angle (half) refers to side cutting edge angle of a single point
tool.
 Standard Point Angle is 118°
 It is 116° to 118° for medium hard steel and cast iron
 It is 125° for hardened steel
 It is 130° to 140° for brass and bronze
 It is only 60° for wood and plastics

17. Helix Angle (ψ)
 Helix angle is the angle between the leading edge of the
land and the axis of the drill. Sometimes it is also called
as spiral angle.
 The helix results in a positive cutting rake
 This angle is equivalent to back rake angle of a single
point cutting tool.
 Usual – 20° to 35° – most common
 Large helix : 45° to 60° suitable for deep holes and softer
work materials
 Small helix : for harder / stronger materials
 Zero helix : spade drills for high production drilling
micro-drilling and hard work materials

18. IES - 1992
A drill for drilling deep holes in aluminum should
have
(a) High helix angle (b) Taper shank
(c) Small point angle (d) No lip

19. GATE- 1997
Helix angle of fast helix drill is normally
(a) 35o
(b) 60o
(c) 90o
(d) 5o

20. IES - 1992
Low helix angle drills are preferred for drilling
holes in
(a) Plastics (b) Copper
(c) Cast steel (d) Carbon steel

21. Cutting Speed in Drilling
 The cutting speed in drilling is the surface speed of the
twist drill.
/ min
1000
DN
V m



22. Drilling Time
 Time for drilling the hole
, min
L
T
fN


23. MRR in Drilling
2
3
, / min
4
D
MRR fN mm
 
  
 

24. Example
A hole with 40-mm diameter and 50-mm depth is to
be drilled in mild steel component. The cutting
speed can be taken as 65 m/min and the feed rate as
0.25 mm/rev. Calculate the machining time and the
material removal rate.

25. Some Formulae for Drilling
 1
( )
2tan
( ) sin
2
( )
2sin
2 / tan
( ) tan
sin
D
Coneheight h
f
Uncut chipthickness t
D
Widthof cut b
r D
Orthogonal rakeangle










 
  
 

26. Video

28. GATE- 2012
In a single pass drilling operation, a through hole of
15 mm diameter is to be drilled in a steel plate of 50
mm thickness. Drill spindle speed is 500 rpm, feed
is 0.2 mm/rev and drill point angle is 118°. Assuming
2 mm clearance at approach and exit, the total drill
time (in seconds) is
(a) 35.1 (b) 32.4
(c) 31.2 (d) 30.1

29. GATE-2014 (PI)
An HSS drill of 20 mm diameter with 5 mm cone
height is used to drill a through hole in a steel work-
piece of 50 mm thickness. Cutting speed of 10
m/min and feed rate of 0.3 mm/rev are used. The
drilling time, in seconds, neglecting the approach
and over travel, is _______

30. IAS - 1994
The time (in minutes) for drilling a hole is given by
where 'h' is the
(a) Length of the drill
(b) Drill diameter
(c) Flute length of the drill
(d) Cone height of the drill.
RPMFeed
hholetheofDepth
t


