ELEMENTS OF MECHANICAL ENGINEERING

Mechanical Engineering Department

LATHE AND DRILLING MACHINES

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.

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

Engine lathe

• Is the most commonly used general purpose lathe used in engineering workshops

• Principle of working

MAJOR PARTS O F LATHE AND THEIR FUNCIONS

MAJOR PARTS O F LATHE AND THEIR FUNCIONS

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.

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

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.

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.

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.

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.

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.

Tool post

• The tool post is mounted on top of the compound slide.

• The tool post holds the tool rigidly.

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.

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.

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.

Lathe Operations

Different types of operations that can be carried out

1. Facing 2. Straight Turning 3. Chamfering 4. Knurling 5. Forming 6. Grooving and parting off7. Drilling 8. Boring 9. Taper turning10. Thread cutting

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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) / 2Lα = Half taper angleD= Large diameterd= Small diameterL= Length of taper

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.

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 lX = Set overD= Large diameterd= Small diameterL= Length of work piecel = Length of taper

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.

Taper Turning by a Taper Turning Attachment

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.

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.

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, 9) Width of bed

Tool Nomenclature

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.

Types Of Drilling Machines

1. Portable drilling machine

2. Bench Drilling Machine (Sensitive drilling machine)

3. Upright drilling machine

4. Radial drilling machine

5. Gang drilling machine

6. Multiple spindle drilling machine

7. Automatic drilling machine

8. Deep hole drilling machine.

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.

Bench Drilling Machine (Sensitive Drilling Machine)

The main parts of the machine

• The main parts of the machine are

• Base,

• Column,

• Table,

• Spindle and

• Driving mechanism.

Radial Drilling Machine

• Radial drilling machine

Drilling Operations

• The different operations that can be performed in a drilling machine are

1) Drilling

2) Reaming

3) Boring

4) Counter boring

5) Counter sinking

6) Spot facing

ReamingDrilling

Boring Counter Boring

Counter Sinking

Spot Facing

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

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.