1. ELEMENTS OF MECHANICAL ENGINEERING
Mechanical Engineering Department

2. LATHE AND DRILLING MACHINES

3. Introduction Metal cutting operations
Manually – by using hand tools such as chisels, files etc.
Machines - machine tools
Machine tools
A machine tool may be defined as a power driven machine which accomplishes the cutting operations
The fundamental machine tools that are used for most of the machining operations are lathe, drilling, tapping, milling, grinding machines.

4. LATHE
Lathe is a machine tool employed generally to produce cylindrical objects.
It is said to be mother of all the machine tools.
Types of lathe
Engine lathe
Speed lathe
Turret lathe
Capstan lathe
CNC lathe

5. Engine lathe
Is the most commonly used general purpose lathe used in engineering workshops
Principle of working

6. MAJOR PARTS O F LATHE AND THEIR FUNCIONS

7. MAJOR PARTS O F LATHE AND THEIR FUNCIONS

11. Bed The bed is the main component of a lathe.
All the major components are mounted on the lathe bed, like tail stock, headstock, carriage, etc. Tailstock and carriage move over the guide ways provided on top face of the bed.
The bed material should have high compressive strength and high wear resistance. Cast iron alloyed with nickel chromium forms a good material for bed.

12. Headstock Headstock is mounted on the left hand side of the lathe bed.
The head stock accommodates gear box, which helps to vary the spindle speed. The gear box also transmits the power to other parts like feed rod and lead screw.
The chuck or face plate is attached to the spindle which provides mechanical means clutching and rotating the work piece.
Head stock is also known as live center

13. Tailstock
The tailstock is mounted on the right hand side of the lathe bed.
The function of the tailstock is to support the work piece, and to accommodate different tools like drill, reaming, boring and tapping, etc.
The tailstock moves on the guide ways over the bed, to accommodate for different length of work piece.
Tailstock is known as dead center.

14. Carriage
The carriage is mounted on the lathe bed, which slides on the guide ways of the bed.
The carriage has various other parts like, cross slide, compound rest, and tool post.

15. Saddle
The saddle is mounted on the bed and slides along the ways.
The cross slide and tool post are mounted on the saddle.
The movement of the saddle is parallel along the axis of the lathe, it is also known as feed.

16. Cross slide
The cross slide is mounted on the top of the saddle. This moves the tool at perpendicular to the work piece or machine axis.
The cross slide can be moved either by rotating the cross slide hand wheel.
The perpendicular distance moved by the cross slide is proportional to the amount of metal removed and it is known as depth of cut.

17. Compound slide
The compound slide (compound rest) is mounted on the top of the cross slide.
The rest part of the compound slide has graduations in degree.
Compound slide is used to obtain taper on the work piece.

18. Tool post
The tool post is mounted on top of the compound slide.
The tool post holds the tool rigidly.

19. Apron
The apron is fastened to the saddle and hangs over the front of the bed.
Apron is fitted with mechanism for both manual and powered movement of the saddle and the carriage.
Split nut engages the Apron with lead screw, which is used to cut internal or external threads.

20. Feed rod Feed rod is a long shaft extending from the feed box.
The power is transmitted from a set of gears from headstock.
The feed rod is used to move the carriage or cross slide for turning, boring and facing operations.

21. Lead screw
The lead screw is a long threaded shaft connected to the headstock.
The lead screw is used only when thread cutting operation is to be carried out on the work piece.
For normal turning operations the lead screw is disengaged.

22. Lathe Operations
Different types of operations that can be carried out
Facing
Straight Turning
Chamfering
Knurling
Forming
Grooving and parting off
Drilling
Boring
Taper turning
Thread cutting

23. Facing
Facing is the process of removing metal from the end of a work piece to produce a flat surface.
The work piece rotates about its axis and the facing tool is fed perpendicular to the axis of lathe.

24. Straight Turning
Turning is the removal of metal from the outer diameter of a rotating cylindrical work piece.
Turning is used to reduce the diameter of the work piece, usually to a specified dimension.

25. Chamfering
It is a process of creating a slope at the end of the work piece.
This process is carried out for removing the unwanted metals and burrs after turning operation.

26. Knurling
Knurling is the process of embossing a required shaped pattern on the surface of the work piece.
This diagram shows the knurling tool pressed against a piece of circular work piece.

27. Parting
Parting off is the operation of cutting a work piece after it has been finished to the desired dimension and shape.
This operation is carried out with a narrow cutting tool known as parting tool.
In parting operation both feed is fixed or locked and depth of cut is controlled properly until the work is cut off in parts.

28. Drilling
Drilling is the operation of producing a cylindrical hole in a work piece using a drill.
The work piece is held in the chuck and the drill is held in the tailstock.
The feed is provided by means of moving the sleeve of the tailstock. The figure shows the drilling operation.

29. Boring
Boring is the operation of enlarging the previously drilled hole.
The operation is carried out by using a single point cutting tool known as boring tool.

30. Taper turning
A taper may be defined as a uniform increase or decrease in diameter of work piece measured along its length.
Taper surface is generated on a cylindrical work piece.
The amount of taper in a work piece is usually specified by the difference in diameters of the taper to its length.
D-Large diameter of taper in mm.
d- Small diameter of taper in mm.
l- Length of tapered part in mm.
α- Angle of taper or half taper angle.

31. Taper Turning Methods
The taper turning is done on a lathe by different methods.
The selection of method depends on length of taper to be generated on the work piece.
The different methods of taper turning are
Taper turning by form tool method
Taper turning by swiveling the compound rest.
Taper turning by offsetting the tail stock
Taper turning by taper turning attachment.

32. Taper Turning by Form Tool Method
The form tool has a cutting edge formed at the desired angle.
The form tool is a replica of the shape (Taper angle) to be produced on the work piece.
The form tool is fed against a rotating work piece; the shape of the tool is reproduced on the work piece.
The form tool method is restricted only for short length tapers.

33. Taper Turning by Swiveling Compound Rest
In this method of taper the half taper angle is calculated.
[The compound rest has rotating base graduated in degrees, which can be rotated to any angle (according to the taper angle).]
In this method the tool is advanced by rotating the compound rest and hand wheel so that the tool moves according to set taper angle.
This method produces taper length larger than form tool method.
Formula which is used to calculate taper angle is tan α = ( D - d) / 2L
α = Half taper angle
D= Large diameter
d= Small diameter
L= Length of taper

34. Taper turning by tailstock offset method
In a lathe the live center and dead center both lies on the same axis.
The work is held between the live and dead center.
The dead center (tailstock) axis is shifted (towards or away from the operator) to the required length on the lathe bed to get taper on the work piece.
In tail stock off set method small taper angle is obtained for longer length work piece.

35. Taper turning by tailstock offset method
The work piece is held between the centers and the carriage is moved on the bed. The tool traces the lathe axis, but the work piece is offset by an angle. Hence taper is generated on the work piece.
(D – d) L
Off set, X =
2 l
X = Set over
D= Large diameter
d= Small diameter
L= Length of work piece
l = Length of taper

36. Taper Turning by a Taper Turning Attachment
A taper turning attachment is fitted on the backside of the lathe bed.
There is a guide bar which guides the tool based on the taper required on the work piece.
The guide bar can be swiveled according to taper angle.
The guide block is connected to the cross slide. The guide block guides the tool.
The cross slide is made free from the lead screw by removing the binder screw.

37. Taper Turning by a Taper Turning Attachment

38. Thread Cutting
Thread cutting is the operation of producing helical groove on a cylindrical surface.
Threads may be square or v threads can be cut on a cylindrical work piece.
The threads of any pitch, shape and size can be cut on a lathe.
A single point cutting tool (V-tool or square tool) is used to cut threads on the work piece.

39. Thread Cutting
For thread cutting operation, the tool is moved automatically in longitudinal direction.
The longitudinal feed should be equal to the pitch of the thread to be cut per revolution of the work.

40. Specification of a Lathe
1.)The length of the bed,
2) The distance between the centers.
3)The swing diameter of work over bed,
4)The swing diameter of work over the carriage,
5) Power input
6)Lead screw details,
7) Number of spindle speeds
8) Feeds, ) Width of bed

41. Tool Nomenclature

42. Drilling machines
Any component manufactured has one or more cylindrical hole in them.
The process of making a hole is known a drilling.
The cutting tool, which is used for making holes, is known as drill.
The drill is a multipoint cutting tool.
Definition: Drilling is the operation of making holes in a work piece using a drill bit.
The hole generated by the rotating drill, which exerts large force on the work piece clamped rigidly on the machine table.
The figure below illustrates a cross section of a hole being cut by a common twist drill.

43. Types Of Drilling Machines
Portable drilling machine
Bench Drilling Machine (Sensitive drilling machine)
Upright drilling machine
Radial drilling machine
Gang drilling machine
Multiple spindle drilling machine
Automatic drilling machine
Deep hole drilling machine.

44. Portable drilling machine
It is a small and compact machine, which can be conveniently held by hand, and drilling operations can be carried out.
These machines are used to drill small holes in large work piece.
Portable machines run at high speeds, powered by electrical motor or pneumatic.
The maximum diameter of hole it can drill is 12 mm. The feed is applied by hand.

45. Bench Drilling Machine (Sensitive Drilling Machine)

46. The main parts of the machine
The main parts of the machine are
Base,
Column,
Table,
Spindle and
Driving mechanism.

47. Radial Drilling Machine

48. Drilling Operations
The different operations that can be performed in a drilling machine are
Drilling
Reaming
Boring
Counter boring
Counter sinking
Spot facing

49. Reaming
Drilling
Boring
Counter Boring

50. Counter Sinking
Spot Facing

51. Drilling Machines Specification
The specification of the radial drilling machine are
Diameter of the column
Length of the column
Length of the arm
Maximum & minimum drilling radius
Spindle speed
Feed.
The other details of the drilling machine are
Maximum diameter of the drill that machine can operate.
Table size
Rise or lowering of the spindle
Spindle speed & feed
Power

52. Twist Drill
Twist drills are rotary end-cutting tools having one or more cutting lips and one or more straight or helical flutes for the passage of chips and cutting fluids. Twist drills are made with straight or tapered shanks, but most have straight shanks.