WORKSHOP TECHNOLOGY 1 (JJ104)

Prepared by:JKM PMS

7 August 2011WORKSHOP TECHNOLOGY 1

JJ104

CHAPTER 5

LATHE MACHINE

OBJECTIVES

• Understand functions of parts of centre lathe machine.

• Understand how work piece held to the lathe machine.

• Understand shapes of tool bits and their function.• Understand angles of a tool bit tip. • Understand materials used in a tool bit. • Understand lathe machine operation.

INTRODUCTION

Purpose : • To rotate a part against a tool whose position it controls. • Useful for fabricating parts and/or features that have a circular

cross section. The spindle is the part of the lathe that rotates.

Workholding attachments : • Chucks, collets, and face plate can be held in the spindle. • The spindle is driven by an electric motor through a system of

belt drives and/or gear trains.• Spindle speed is controlled by varying the geometry of the

drive train.

INTRODUCTION (cont.)

Tailstock :• Can be used to support the end of the workpiece with a

center, or …• …to hold tools for drilling, reaming, threading, or cutting

tapers. • It can be adjusted in position along the ways to accommodate

different length workpieces.

Machine Tool Basics - Intro to Lathe Operations - YouTube2.flv

PARTS OF LATHE MACHINE

PARTS OF LATHE MACHINE (cont.)

WORKSHOP TECHNOLOGY 1 JJ104

PARTS OF LATHE MACHINE (cont.)

PARTS OF LATHE MACHINE (cont.)

• Bed : - Supports all major components of the lathe.• Carriage: - Slides along the ways and consists of an assembly

of the cross-slide, tool post and apron.• Tool post: where cutting tools mounted• Cross-slide: moves radially in and out, controlling the radial

position of the cutting tool• Apron: equipped with mechanisms for both manual &

mechanized movement of the carriage and the cross-slide by means of the lead screw

• Headstock: - Fixed to the bed and is equipped with motors, pulleys and V-belts that supply power to spindle at various rotational speeds.

PARTS OF LATHE MACHINE (cont.)

• Tailstock : - Can slide along the ways and be clamped at any position, supports the other end of workpiece.

• Tail center: - To hold the end of long pieces of workpiece. • Feed rod & lead screw: - The feed rod is powered by a set of

gears through the headstock. It rotates during the lathe operation and provide movement to the carriage and the cross-slide. Closing a half nut lever around the lead screw engages it with the carriage.

• Chuck: - To hold the workpiece.

WORKHOLDING DEVICES

Introduction

• Workholding device is important, particularly in machine tools and machining operations

• Must hold workpiece securely• One end of the workpiece is clamped to the spindle by the

workholding device• Types of workholding devices : Chuck, Collet, Face plate ,

Steady Rest, Follow Rest

1. Universal Chuck - 3 Jaw Chuck

Use to hold a work piece which are cylinder or hexagon. For facing or center drilling the end of the work piece.

Figure: Shows 3 positions 3 jaw chuck hold a work piece.

Be careful when use position (a) and (c) because the work piece can easily slip when machining at high feed rate and high depth of cut.

WORKHOLDING DEVICES (cont.)

2.Independent chuck (4 jaw chuck)

Can hold work piece more precise rather than 3 jaw chuck.

Figure: Shows 3 positions 4 jaw chuck hold a work piece.

WORKHOLDING DEVICES (cont.)

3.Collet chuck

Use to hold and machined small components

Generally for workpiece with a maximum diameter of 25mm

.

Figure: Collet chuck

WORKHOLDING DEVICES (cont.)

4. Steady rest

Used to support a long workpiece which is 3 times its diameter.

To prevent workpiece from bending

WORKHOLDING DEVICES (cont.)

5. Follow rest

Suitable for small and long workpiece during parallel lathe machining

To minimize flex under the pressure of the cutting tools

WORKHOLDING DEVICES (cont.)

6. Face Plate

Used for clamping irregularly shaped workpieces.

The plates are round and have several slots and holes through which the workpiece is clamped.

SmithyCo's Channel - YouTube.flv

WORKHOLDING DEVICES (cont.)

TO BE CONTINUE….

WORKHOLDING DEVICES (cont.)

Definitions:• A piece of high-strength metal, usually steel, ground to

make single-point cutting tools for metal-cutting operations.

• In lathe, it refers to a non-rotary cutting tool and also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be sharpened or reshaped as needed. The ground tool bit is held rigidly by a tool holder while it is cutting.

• Cutting tools must be made of a material harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal-cutting process.

TOOL BITS

Various shape of Tool bit

TOOL BITS (cont.)

Figure: Standard Shapes

Various shape of Tool bit (cont.)

• Facing tools are ground to provide clearance with a center.

• Roughing tools have a small side relief angle to leave more material to support the cutting edge during deep cuts.

• Finishing tools have a more rounded nose to provide a finer finish.

• Round nose tools are for lighter turning. They have no back or side rake to permit cutting in either direction.

• Left hand cutting tools are designed to cut best when traveling from left to right.

• Video

TOOL BITS (cont.)

8/6/11

ANGLE OF TOOL BIT TIP

Figure: Single point cutting tools

8/6/11

ANGLE OF TOOL BIT TIP (cont.)

Figure: Tool bit nomenclature

8/6/11

Various angle in a cutting tool have important functions in machining operation.

1. Rake angle: Control direction of chip flow and the strength of the tool tip.

2. Side rake angle: Control direction of chip flow. Angle typically about 5°.

3. Cutting-edge angle: Affects chip formation, tool strength, and cutting force to various degree. Angle typically about 15°.

ANGLE OF TOOL BIT TIP (cont.)

4. Relief angle: Control interference and rubbing at the tool-work piece interface.

If it too large, the tool tip may chip off, if it too small, flank wear may be excessive.

Relief angle typically are 5°.

5. Nose radius: Affects surface finish and tool tip strength.

The smaller the nose radius(sharp tool), the rougher the surface finish of the work piece and the lower the strength of the tool.

How ever, long nose radius can lead to tool chatter.

ANGLE OF TOOL BIT TIP (cont.)

1. Carbon steel

•Contain 0.9%-1.2% of carbon•The oldest of tool material and widely use.•Advantages: Cheap and easily shape and sharpened.•Disadvantage: Do not have sufficient hot hardness and wear resistance for cutting at high speed when the temperature rises.

2. High-speed steel(HSS)

•Contain: Tungsten, chromium, cobalt, molybdenum.•Use to machine at higher speed, and complex such as drilling.•Advantage: High toughness, resistance to fracture.•Disadvantage: Low hot hardness.

TOOL BIT MATERIAL

TOOL BIT MATERIAL (cont.)

3. Stellite

• Contain 25%-35% chromium, 4%-25% Tungsten, 1%-3% carbon and the rest is cobalt.

• Use for roughing cuts at high feed and speed-twice the rates possible with HSS

• Advantage: high hardness, good wear resistance• Disadvantage: not as tough as HSS and sensitive to impact

forces.

TOOL BIT MATERIAL (cont.)

4. Ceramic

• Consist of aluminium oxide.• Moderately inexpensive• Advantage: High hardness, high wear resistance, extremely resistant to

heat, desirable in high speed applications.• Do not need coolant during machining.• Disadvantage: High fragility. Ceramics are considered unpredictable

under unfavorable conditions. The most common ceramic materials are based on alumina (aluminium oxide), silicon nitride and silicon carbide. Used almost exclusively on turning tool bits. Hardness up to about HRC 93. Sharp cutting edges and positive rake angles are to be avoided.

5. Carbide

• 2 major group of carbide (Tungsten Carbide and Titanium Carbide)• Consist of 82% Carbide, 10% titanium and tungsten and 8% cobalt.• Advantage: Very hard and can stand with high temperature• Disadvantage: Low wear resistance• Triple the rates possible with HSS (in term of cutting speed during

machining)

6. Diamond

• Use for surface finish• High accuracy machining(0.002-0.005 mm)• Disadvantage: easy fracture low impact resistance.

TOOL BIT MATERIAL (cont.)

Turning: To produce straight, conical, curve or groove work piece.

Boring: To enlarge a hole or cylindrical cavity made by previous process or to produce circular internal grooves.

Facing: To produce flat surface at the end of the part and perpendicular to its axis.

Drilling: To produce a hole which may be followed by boring to improve its dimensional accuracy and surface finish.

LATHE MACHINE OPERATION

Knurling: To produce a regularly shaped roughness on cylindrical surface(making knobs)

Tread cutting: To produce external/internal threads.

Off-centre turning: To produce various axis symmetric shapes for functional or aesthetic purpose.

LATHE MACHINE OPERATION (cont.)