Basic Elements, Working Principle, Types of Operations with block diagram: Lathe Machine - Centre Lathe, Drilling Machines, Grinding Machines.

1. Basic Mechanical Engineering
By
Nitin G Shekapure
Unit IV
Machine Tools (L24 To 28)
N
itin
Shekapure

2. By: Nitin Shekapure
Unit IV
Machine Tools
Basic Elements, Working Principle, Types of Operations with block diagram:
Lathe Machine - Centre Lathe, Drilling Machines, Grinding Machines.
N
itin
Shekapure

3. Lathe Machine
• Lathe is one of the most versatile and widely used machine
tools all over the world. It is commonly known as the mother of
all other machine tool.
• The main function of a lathe is to remove metal from a job
(Work piece) to give it the required shape and size.
N
itin
Shekapure

4. Working Principal Lathe Machine
• The job (work piece) is securely and rigidly held in the chuck or in between
centers on the lathe machine and then turn it against a single point cutting
tool which will remove metal from the job in the form of chips.
• An engine lathe is the most basic and simplest form of the lathe.
• It derives its name from the early lathes, which obtained their power from
engines.
• Besides the simple turning operation as described above, lathe can be used
to carry out other operations also, such as drilling, reaming, boring, taper
turning, knurling, screw-thread cutting, grinding etc.
N
itin
Shekapure

5. Types of Lathe
 Speed Lathe
 Engine Lathe
 Bench Lathe
 Tool room lathe
 Capstan and Turret Lathe
 CNC Lathe (Automatic Lathe)
N
itin
Shekapure

6. Speed Lathe
Speed lathe is simplest of all types of lathes in construction and operation.
The important parts of speed lathe are following-
(1) Bed
(2) Headstock
(3) Tailstock, and
(4) Tool post mounted on an adjustable slide.
It has no feed box, Leadscrew or conventional type of carriage. The tool is
mounted on the adjustable slide and is fed into the work by hand control.
The speed lathe finds applications where cutting force is least such as in wood
working, spinning, centering, polishing, winding, buffing etc.
This lathe has been so named because of the very high speed of the headstock
spindle.
N
itin
Shekapure

7. Engine Lathe (Centre Lathe)
The term “engine” is associated with this lathe due to the fact that in the very
early days of its development it was driven by steam engine.
This lathe is the important member of the lathe family and is the most widely
used.
Similar to the speed lathe, the engine lathe has all the basic parts, e.g., bed,
headstock, and tailstock.
But its headstock is much more robust in construction and contains additional
mechanism for driving the lathe spindle at multiple speeds.
Centre lathes or engine lathes are classified according to methods of
transmitting power to the machine. The power may be transmitted by means
of belt, electric motor or through gears.
N
itin
Shekapure

8. Speed Lathe
This is a small lathe usually mounted on a bench. It has practically all the parts
of an engine lathe or speed lathe and it performs almost all the operations.
This is used for small and precision work.
N
itin
Shekapure

9. Tool Room Lathe
This lathe has features similar to an engine lathe but it is much more
accurately built.
It has a wide range of spindle speeds ranging from a very low to a quite high
speed up to 2500 rpm.
This lathe is mainly used for precision work on tools, dies, gauges and in
machining work where accuracy is needed.
N
itin
Shekapure

10. Capstan and Turret Lathe
The development of these lathes results from the technological advancement
of the engine lathe and these are vastly used for mass production work.
The distinguishing feature of this type of lathe is that the tailstock of an engine
lathe is replaced by a hexagonal turret, on the face of which multiple tools may
be fitted and fed into the work in proper sequence.
Due to this arrangement, several different types of operations can be done on a
job without re-setting of work or tools, and a number of identical parts can be
produced in the minimum time.
N
itin
Shekapure

11. These lathes are so designed that all the working and job handling
movements of the complete manufacturing process for a job are
done automatically.
These are high speed, heavy duty, mass production lathes with
complete automatic control.
CNC Lathe
N
itin
Shekapure

12. CONSTRUCTION OF LATHE MACHINE
A simple lathe comprises of a bed made of grey cast iron on which headstock,
tailstock, carriage and other components of lathe are mounted. Figure shows
the different parts of engine lathe or central lathe. The major parts of lathe
machine are given as under:
1. Bed
2. Head stock
3. Tailstock
4. Carriage
5. Feed mechanism
6. Thread cutting mechanism
N
itin
Shekapure

13. N
itin
Shekapure

14. Major Parts of Lathe Machine
Bed
The bed of a lathe machine is the base on which all other parts of lathe are
mounted.
It is massive and rigid single piece casting made to support other active parts
of lathe.
On left end of the bed, headstock of lathe machine is located while on right
side tailstock is located.
The carriage of the machine rests over the bed and slides on it. On the top of
the bed there are two sets of guideways -innerways and outerways. The
innerways provide sliding surfaces for the tailstock and the outerways for the
carriage. The guideways of the lathe bed may be flat and inverted V shape.
Generally cast iron alloyed with nickel and chromium material is used for
manufacturing of the lathe bed.
N
itin
Shekapure

15. It is used to support all the elements and to withstand cutting
forces during the operation.
Bed
Function:
Major Parts of Lathe Machine
N
itin
Shekapure

16. Head Stock
The main function of headstock is to transmit power to the different parts of a
lathe.
It comprises of the headstock casting to accommodate all the parts within it
including gear train arrangement.
The main spindle is adjusted in it, which possesses live centre to which the
work can be attached. It supports the work and revolves with the work, fitted
into the main spindle of the headstock.
The cone pulley is also attached with this arrangement, which is used to get
various spindle speed through electric motor.
The back gear arrangement is used for obtaining a wide range of slower
speeds. Some gears called change wheels are used to produce different
velocity ratio required for thread cutting.
Major Parts of Lathe Machine
N
itin
Shekapure

17. • To support the spindle
• To carry driving mechanism for the work-piece
• To give multiple speeds to the spindle
Function:
Head Stock Major Parts of Lathe Machine
N
itin
Shekapure

18. Tail Stock
Figure shows the tail stock of central
lathe, which is commonly used for the
objective of primarily giving an outer
bearing and support the circular job being
turned on centers. Tail stock can be easily set or adjusted for alignment or non-
alignment with respect to the spindle centre and carries a centre called dead
centre for supporting one end of the work. Both live and dead centers have 60°
conical points to fit centre holes in the circular job, the other end tapering to
allow for good fitting into the spindles. The dead centre can be mounted in ball
bearing so that it rotates with the job avoiding friction of the job with dead
centre as it important to hold heavy jobs.
Major Parts of Lathe Machine
N
itin
Shekapure

19. Function:
Tail Stock Major Parts of Lathe Machine
• To support the other part of the workpiece when it is being
machined
• To hold the tool to perform operations like drilling, reaming
etc.
N
itin
Shekapure

20. Carriage
Carriage is mounted on the outer guide ways of lathe bed and it can move in a
direction parallel to the spindle axis.
It comprises of important parts such as apron, cross-slide, saddle, compound
rest, and tool post.
The lower part of the carriage is termed the apron in which there are gears to
constitute apron mechanism for adjusting the direction of the feed using
clutch mechanism and the split half nut for automatic feed.
The cross-slide is basically mounted on the carriage, which generally travels at
right angles to the spindle axis.
On the cross-slide, a saddle is mounted in which the compound rest is adjusted
which can rotate and fix to any desired angle.
The compound rest slide is actuated by a screw, which rotates in a nut fixed to
the saddle.
Major Parts of Lathe Machine
N
itin
Shekapure

21. Major Parts of Lathe Machine
• To support, guide, and feed the tool against the workpiece
during the operation
Function:
Carriage
N
itin
Shekapure

22. Feed Mechanism
Major Parts of Lathe Machine
The movement of the tool relative to the workpiece is known as
feed.
The lathe tool can have longitudinal, cross, and angular feed.
The feed mech. has various units through which motion is
transmitted from the headstock spindle to the carriage.
Function:
• It is used to transmit the motion from headstock spindle to
the carriage.
N
itin
Shekapure

23. Thread Cutting Mechanism
The half nut or split nut is used for thread cutting in a lathe.
It engages or disengages the carriage with the lead screw so
that the rotation of the leadscrew is used to traverse the tool
along the workpiece to cut screw threads.
The direction in which the carriage moves depends upon the
position of the feed reverse lever on the headstock.
In other times, it is disengaged and remained stationary
Major Parts of Lathe Machine
N
itin
Shekapure

24. Lead Screw
• Very Important part of Lathe
• Long threaded shaft driven by feed drive
• Provides mechanized/automatic motion to carriage for screw
threads on the job
• Lead Screw is MUST for Threading Operations on Lathe
• Split Nut or Half Nut Mechanism converts rotary motion of
lead screw to linear motion of carriage
N
itin
Shekapure

25. Specification of Lathe
The size of a lathe is generally specified by the following means:
a) Swing or maximum diameter that can be rotated over the bed ways
b) Maximum length of the job that can be held between head stock and tail
stock centres
c) Bed length, which may include head stock length also
d) Maximum diameter of the bar that can pass through spindle or collect
chuck of capstan lathe.
N
itin
Shekapure

26. Specification of Lathe
N
itin
Shekapure

27. Lathe Machine Parts – Functions
N
itin
Shekapure

28. Lathe Operations
The various operations that can be performed on a lathe are:
1. Turning
2. Eccentric turning
3. Taper turning
4. Thread cutting
5. Facing.
6. Knurling
7. Chamfering.
8. Parting off
9. Grooving
10. Drilling
11. Boring
N
itin
Shekapure

29. Turning
• Most basic operation done on lathe machine
• Job or work piece is turned (rotated) using rotary motion of spindle,
hence lathe is also called Turning Machine!
• Lathe operator is called “Turner”!
• Removal of material from a cylindrical work-piece or job
• To reduce diameter of cylindrical job
• Tool motion parallel to the axis of lathe
• Tool used is called “Turning Tool” and it is “Single Point Cutting Tool”
• Rough turning, using roughing tool or knife tool
• Finish turning using finishing tool
N
itin
Shekapure

30. Basic Turning Operations
N
itin
Shekapure

31. Eccentric Turning
• To reduce diameter of about an axis offset from axis of job
• Turned portion remains eccentric to the rest of work piece
• Four jaw chuck is used to hold the job
• Axis of job is kept offset to the axis of lathe during turning operation
N
itin
Shekapure

32. Taper Turning
• To reduce diameter of work piece uniformly along the length of work piece
• Taper turning using “form tool”
• Taper turning by “tailstock set over” method
• Taper turning using “taper turning attachment”
• Taper turning by “swiveling the compound rest”
N
itin
Shekapure

33. Taper Turning
N
itin
Shekapure

34. Taper Turning
N
itin
Shekapure

35. Facing
• Removal of material from end surface of the work piece or job
• To have a reference plane to mark and measure the step lengths of work
• To have a face at right angle to the axis of the work
• To reduce length of job
• To maintain the total length of the work
• Facing Tool is used
• Tool motion is perpendicular to axis of lathe
• To produce flat surface
(especially after parting off operations)
N
itin
Shekapure

36. Facing
N
itin
Shekapure

37. • Process of beveling the sharp edges of work piece
• Chamfered jobs avoids injuries to hands of persons handling the job
• Provides aesthetic look to the work piece
• Chamfering tool is used to permit easy assembly of mating parts
• Chamfer specified as CH 2 x 45 (2 mm deep at an angle of 45 degrees)
Chamfering
N
itin
Shekapure

38. Grooving or Groove Cutting
• To create narrow groove on cylindrical work piece
• Shape of tool is replicated as shape of groove
• Operation also known as Form Turning!
• Square Groove, Round Groove and ‘V’ Type Grooves
N
itin
Shekapure

39. Parting
• Process of cutting work piece into 2 parts
• Extension of grooving operation where feed is provided till axis of work
piece
• Care needs to be taken when work piece splits into two parts
N
itin
Shekapure

40. Knurling
• Process of embossing a diamond shaped regular pattern on the surface of job
• Tool used is called “Knurling Tool”
• Types: Parallel or Straight Knurling, Diamond or Criss-Cross Knurling, Concave
or Convex Knurling
• Squeezing metal into peaks and valleys using plastic deformation
• Provides non-slip grip to the job
• Aesthetic or Decorative look
N
itin
Shekapure

41. Knurling
N
itin
Shekapure

42. Drilling
• Process of making a circular hole in cylindrical job
• Tailstock is used to hold cutting tool which is called as “Drill”
• Drill is feed against rotating job by rotating hand wheel of tailstock in
clockwise direction
• After making hole, the drill is withdrawn by rotating the tailstock handle
in anti-clockwise direction
N
itin
Shekapure

43. Drilling
N
itin
Shekapure

44. • Process of enlarging already existing hole in the job
• Tailstock is used to hold the tool
• Skill of operator plays imp role
• Tool used is called as “Boring Tool”
Boring
N
itin
Shekapure

45. Threading or Thread Cutting
• Process of creating threads in the form of helical groove on the surface of cylindrical
job
• Tool used is called “Thread Cutting Tool”
• Point geometry of thread cutting tool creates desired type of thread.
• Tool motion is parallel to axis of lathe
• For 1 revolution of job, tool travels automatically by distance equal to the pitch of the
thread
• Fixed relation between rotary motion of job and
linear motion of tool is achieved by engaging
carriage with lead screw using half-nut or
split-nut mechanism
N
itin
Shekapure

46. Drilling Machine
N
itin
Shekapure

47. Two components can be connected to each other with the
help of nuts and bolts, the cylindrical holes need to be
made in the components.
DRILLING
• Its the process of making the cylindrical hole in the
work piece.
• Drilling is the operation of producing circular hole in the
work-piece by using a rotating cutter called DRILL.
• The machine used for drilling is called drilling machine.
Drilling Machine
N
itin
Shekapure

48. Types of drilling machine
1. Portable drilling machine
2. Sensitive or bench drilling machine
3. Upright drilling machine
4. Radial drilling machine
5. Gang drilling machine
6. Multi-spindle drilling machine
7. Deep hole drilling machine
8. Automatic drilling machine
N
itin
Shekapure

49. Principal and operation
• In drilling machine work piece is firmly clamped.
• The cutting tool drill is fitted in to the spindle of the
drilling machine.
• Spindle and drill rotate at the desired speed.
• The rotating drill removes the material from the work
piece in the form of chips, so as to produce the
cylindrical hole
N
itin
Shekapure

50. Basic elements
Base: lower most part that supports the entire structure.
Worktable: it is mounted on the column, it has two
types of motion: Up and down and the swing
about the axis of the column it supports the work
piece.
Spindle: it provides the rotary motion.
Drilling head: it is mounted on the top of column.
It contains drive mechanism and feed mechanism.
Drive mechanism : it mainly consists of electric motor
and gear box ,it is used for driving the spindle(drill)
Feed mech: it is used for feeding the spindle against the
work piece ,it can be power or hand feed.
N
itin
Shekapure

51. • Drilling: process of making cylindrical hole.
• Boring: process of enlarging the existing hole to meet the required
size and finish, drilling larger diameter holes, boring tool is used.
• Spot facing: process of enlarging and making a smooth furnished
hole, it is similar to that if counter boring except in spot facing the
depth of the enlarged hole is very small it is used to provide a seat for
the washer.
• Counter sinking: counter sink is the conical hole drilled in the work
piece to accommodate the flat head screw, rivets to be fitted in the
hole, process of champering the entrance of a drilled hole.
• Tapping: Process of cutting internal threads with a thread tool called
as tap.
Types of operation
N
itin
Shekapure

52. Types of operation
N
itin
Shekapure

53. Drill Bits
N
itin
Shekapure

54. Drill Bit
N
itin
Shekapure

55. Pillar or upright drilling machine
• It is used for medium duty works.
• It is used for drilling holes up to 75mm in diam.
• Spindle is driven by electric motor through gear drive as it
provides wide range of spindle speeds.
• Up and down motion of the work table is controlled by lead
screw
• According to the depth of hole to be drilled the worktable
is moved in Up and down direction.
N
itin
Shekapure

56. Precautions for Drilling machine
• Lubrication is important to remove heat and friction.
• Machines should be cleaned after use
• Chips should be removed using brush.
• T-slots, grooves, spindles sleeves, belts, pulley should be
cleaned.
• Machines should be lightly oiled to prevent from rusting
N
itin
Shekapure

57. Grinding
N
itin
Shekapure

58. Grinding
• Grinding is a surface finishing operation where
very thin layer of material is removed in the
form of dust particles.
• Thickness of material removed is in range of
0.25 to 0.50 mm.
• Tool used is a abrasive wheel.
N
itin
Shekapure

59. Abrasives
• Abrasive is the material employed for sharpening, grinding
and polishing operations.
• Natural abrasive – emery, corundum, quartz, sandstone,
diamond, etc.
• Artificial abrasive – carborundum, aloxite, alundum, etc.
N
itin
Shekapure

60. Applications of abrasives
Corundum: is a natural mineral which consists of aluminium oxide.
Hardest natural substance after diamond
Used for shaping, finishing and polishing other tools
Emery: natural abrasive consisting of aluminium oxide and little
amount of iron oxide
Silicon carbide: synthetic abrasive harder than aluminium oxide
Used to grind metals like iron, brass and soft bronze
Used in non metals like wood and leather industries
N
itin
Shekapure

61. • Zirconia aluminia: it is a mixture of zirconium oxide and
aluminium oxide
– Used in casting and foundry industries
• Cubic boron nitride: is made up of boron nitride with a cubic
crystalline structure
– Used for hard coating material
Applications of abrasives
N
itin
Shekapure

62. Grinding Machine
Grinding machine is a power operated machine tool where, the
work piece is fed against constantly rotating abrasive wheel to
remove thin layer of material from work.
N
itin
Shekapure

63. Principle of grinding machines
• Work piece is fed against the rotating abrasive wheel.
• Due to action of rubbing or friction between the abrasive
particles and work piece material is removed.
N
itin
Shekapure

64. Classification of grinding machine
• Bench grinding machine
• Surface grinding machine
• Cylindrical grinding machine
• Center less grinding machine
• Internal grinding machine
• Special purpose grinding machine
N
itin
Shekapure

65. Surface grinding machine
• It is machine basically used to grind flat surface
• Job is mounted to a table which moves longitudinally
as well as in transverse direction
• Manual feed or power feed
• Work piece can clamped in two ways
– Manual clamps
– Magnetic chuck
N
itin
Shekapure

66. Working
• Work piece is clamped to the table by operating magnetic chuck.
• Required grade of grinding tool is fixed to spindle.
• Grinding operation is carried out be operating both table traverse wheel
and vertical feed hand wheel.
N
itin
Shekapure

67. Cylindrical grinding machine
• It is a process of grinding curved surfaces.
• Surface may be straight or tapered.
• Work piece is mounted on two centers, one is tailstock
centre and the other is headstock centre.
• Head stock center may or may not revolve.
N
itin
Shekapure

68. Cylindrical grinding machine
N
itin
Shekapure

69. Centre less grinding machine
• It is used to grind curved surface work piece which are long and
slender.
• Work piece rests on a work-rest blade and is backed by a
second wheel called as regulating wheel.
• Grinding wheel pushes the work piece down the work-rest
blade against the regulating wheel.
N
itin
Shekapure

70. Centre less grinding machine
N
itin
Shekapure

71. Cutting terminology
• Speed : it is the peripheral speed of the work piece per unit
time. (m/min)
• Feed : it is the distance travelled by the tool during each
revolution of the work piece. (mm/revolution).
• Depth of cut : it is the perpendicular distance measured from
the original surface to the machined surface of the work
piece. (mm)
N
itin
Shekapure