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Premium member Presentation Transcript Slide 1: Unite-II LATHE Unit II Lathe: Introduction, type, construction of simple lathe, mechanism and attachments for various operations, machine specifications, basis for selection of cutting speed, feed and depth of cut, time estimation for turning operations such as facing, step turning, taper turning, threading, knurling. [8 Hrs.] Two Question (i.e. 26 Marks) Numerical of 7 to 8 Theory of 17 to 26 1 Slide 2: Introduction A lathe is a machine tool which spins a block of material to perform various operations 2 Slide 3: 3 Slide 4: Lathe is a machine, which removes the metal from a piece of work to the required shape & size operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the work-piece to create an object which has symmetry about an axis of rotation. Introduction 4 Slide 5: 5 Slide 6: 6 Forces in turning Cutting force: acts downward on the tool tip Thrust force: acts in the longitudinal direction Radial force: acts in the radial direction Roughing and Finishing Cuts Rough cut: high speed cut with little regard for dimensional tolerance Finishing cut: lower feed rate and depth of cut Tool Materials, Feeds, and Cutting Speeds See table 22.4 Cutting Fluids See table 22.5 Turning Parameters History : History The origin of turning dates to around 1300BC when the Egyptians first developed a two-person lathe. One person would turn the wood work piece with a rope while the other used a sharp tool to cut shapes in the wood The Romans improved the Egyptian design with the addition of a turning bow. Early bow lathes were also developed and used in Germany, France and Britain. 7 Slide 8: History 8 History : History In the Middle Ages a pedal replaced hand-operated turning, freeing both the craftsman's hands to hold the woodturning tools. The pedal was usually connected to a pole, often a straight-grained sapling. The system today is called the "spring pole" lathe ( Pole-lathe). 9 History : History During the industrial revolution, mechanized power was applied to the lathe via steam engines and line shafting, allowing faster and easier work. Between the late 19th and mid 20th centuries, individual electric motors at each lathe replaced line shafting as the power source. Beginning in the 1950s, servomechanisms were applied to the control of lathes and other machine tools via numerical control (NC), 10 Machine Classification : Machine Classification Size designation Swing - maximum diameter that can be rotated on the lathe 2x’s distance from spindle center line to ways Maximum distance between centers 11 Size of Lathe : Size of Lathe Workpiece Length Swing Size of Lathe .. : Size of Lathe .. Example: 300 - 1500 Lathe Maximum Diameter of Workpiece that can be machined = SWING (= 300 mm) Maximum Length of Workpiece that can be held between Centers (=1500 mm) Types of Lathes : Types of Lathes Speed Simple construction of a head stock and tail stock with a tool post. Used for wood turning, metal polishing, or metal spinning.1200-3600rpm Engine Most frequently used lathe Heavy duty power drive for most tool movements Size range 12”x24” to 24”x48” - can be larger Bench Lathe A bench top model usually of low power used to make precision machine small work pieces 14 Types of Lathes : Types of Lathes Tool room Greater accuracy More versatility Wider range of speeds and feeds Turret Hex turret replaces tailstock Multiple tools set to machine part High production rates Still may require some operator skill 15 Turret Lathes : Turret Lathes Capable of performing multiple cutting operations on the same workpiece Turning Boring Drilling Thread cutting Facing Turret lathes are very versatile Types of turret lathes Ram-type: ram slides in a separate base on the saddle Saddle type: more heavily constructed Used to machine large workpeiceces 16 Types of Lathes : Types of Lathes Automatic Similar to turret A lathe in which the work piece is automatically fed and removed without use of an operator. Cutting operations are automatically controlled by sequencer of some form Capable of simultaneous cuts Can be a cam controlled mechanism Can be single spindle or multiple spindle 17 Types of Lathes : Types of Lathes Tracer Hydraulic attachment used to copy the shape of a part from a master. lathe that has the ability to follow a template to copy a shape or contour. Machine tools with attachments Capable of turning parts with various contours A tracer finger follows the template and guides the cutting tool 18 Types of Lathes : Types of Lathes CNC Computer controlled Wide variety of process capability multiple axis Indexing and contouring head On- line and off- line programming available Computer Numerical Controls (CNC) Equipped with one or more turrets Each turret is equipped with a variety of tools Performs several operations on different surfaces of the work piece 19 Computer Numerically Controlled Lathes : Computer Numerically Controlled Lathes Fig : A computer numerical control lathe. Note the two turrets on this machine. 20 Slide 21: Component Description 21 Lathe Basics : Lathe Basics 22 Lathe Basics : Lathe Basics Headstock 23 Lathe Basics : Lathe Basics Bedways 24 Lathe Basics : Lathe Basics Carriage/Apron 25 Lathe Basics : Lathe Basics Tailstock 26 Lathe Basics : Lathe Basics Cross Slide APRON Half Nut Lever Friction-clutch Control Lead Screw Bed TAILSTOCK Carriage Hand Wheel Tailstock Spindle Clamp Feed Change Lever Tool Post Compound Rest Saddle BED WAYS Motor Drive Gear Box Feed Reverse Lever HEADSTOCK Spindle Nose 27 Lathe Drive Mechanism : Lathe Drive Mechanism Belts are moved from pulley to pulley to change speeds (rpm). Pulley System without back gear: 4 High range speeds Pulley System with back gear: 4 Low range speeds 28 Carriage Feed : Carriage Feed A. Longitudinal Feed or “Turning” - The tool is fed along the work. C. Cross Feed or “Facing” – The tool is fed across the work. 29 Slide 30: Carriage Feed Power Feed for: Turning Facing Used for greater control and accuracy. Speed controlled by the “Quick Change Gear Box” 30 Slide 31: Carriage and Apron The controls on the carriage and apron control all the tool and carriage movement. 31 Lathe Carriage and Apron : Lathe Carriage and Apron Compound Rest Knob Half Nut Lever Carriage Lock Screw Apron Hand Wheel Apron Feed Change Lever Compound Rest Power Feed Clutch Cross Slide Cross Feed Knob Tool Post 32 Slide 33: Carriage and Apron Apron Hand-wheel: Turning Cross-feed knob: Facing Apron Feed-change lever: Selects power feed between turning and facing Power Feed Clutch: Engages the power feed 33 Apron Hand Wheel : Apron Hand Wheel Apron Hand Wheel Used to move tool along the work - for Turning (Longitudinal Feed) 34 Cross Feed Knob : Cross Feed Knob Cross Feed Knob Used to move cutting tool across the end of the stock - Facing (Cross Feed) 35 Power Feed Clutch : Power Feed Clutch Power Feed Clutch Engages the power feed for turning or facing operations 36 Apron Feed Change Lever : Apron Feed Change Lever Apron Feed Change Lever Switches power feed between turning and facing directions 37 Chuck : Chuck Three Jaw Chuck - For holding cylindrical stock centered. - For facing/center drilling the end of your aluminum stock 38 Chucks : Chucks Used extensively for holding work for lathe machining operations Work large or unusual shape Most commonly used lathe chucks Three-jaw universal Four-jaw independent Collet chuck 39 Slide 40: Work Holding Devices Fig : (a) and (b) Schematic illustrations of a draw-in-type collets. The workpiece is placed in the collet hole, and the conical surfaces of the collet are forced inward by pulling it with a draw bar into the sleeve. (c) A push-out type collet. (d) Workholding of a part on a face plate. 40 Three jaw chuck : Three jaw chuck - For holding cylindrical stock centered. - For facing/center drilling the end of your aluminum stock Four-Jaw Chuck - This is independent chuck generally has four jaws , which are adjusted individually on the chuck face by means of adjusting screws 41 Slide 42: Thin jobs can be held by means of magnetic chucks. Collet Chuck Magnetic Chuck Collet chuck is used to hold small workpieces Thin jobs can be held by means of magnetic chucks. 42 Three-jaw Universal Chuck : Three-jaw Universal Chuck Holds round and hexagonal work Grasps work quickly and accurate within few thousandths/inch Three jaws move simultaneously whenadjusted by chuck wrench Caused by scroll plate into which all three jaws fit Two sets of jaw: outside chucking and inside chucking 43 Three-jaw Universal Chuck : Three-jaw Universal Chuck 44 Four-Jaw Independent Chuck : Four-Jaw Independent Chuck Used to hold round, square, hexagonal, and irregularly shaped workpieces Has four jaws Each can be adjusted independently by chuck wrench Jaws can be reversed to hold work by inside diameter 45 Four-Jaw Independent Chucks : Four-Jaw Independent Chucks 46 Headstock Spindle Types : Headstock Spindle Types Threaded spindle nose Screws on in a clockwise direction Tapered spindle nose Held by lock nut that tightens on chuck Cam-lock spindle nose Held by tightening cam-locks using T-wrench Chuck aligned by taper on spindle nose 47 Lathe Cam-Lock Spindle : Lathe Cam-Lock Spindle 48 Lathe Threaded Spindle : Lathe Threaded Spindle 49 Threaded Spindle Nose : Threaded Spindle Nose 50 Tapered Spindle Nose : Tapered Spindle Nose 51 Cam Lock Spindle Nose : Cam Lock Spindle Nose 52 Collet Chucks : Collet Chucks Most accurate chuck Used for high-precision work Spring collets available to hold round, square, or hexagon-shaped workpieces Each collet has range of only few thousandths of an inch over or under size stamped on collet 53 Spring Collet Chucks : Spring Collet Chucks Spring-collet chuck One form: Handwheel draws collet into tapered adapter Another form: Uses chuck wrench to tighten collet on workpiece Can hold larger work than draw-in type 54 Spring Collet Chucks : Spring Collet Chucks 55 Spring Collet Chucks : Spring Collet Chucks 56 Jacobs Collet Chuck : Jacobs Collet Chuck Jacobs collet chuck Utilizes impact-tightening handwheel to close collets Wider range than spring-collet chuck 57 Jacobs Collet Chuck : Jacobs Collet Chuck 58 Magnetic Chucks : Magnetic Chucks Used to hold iron or steel parts that are too thin or may be damaged if held in conventional chuck Fitted to an adapter mounted on headstock spindle Used only for light cuts and for special grinding applications 59 Magnetic Chucks : Magnetic Chucks 60 Faceplates : Faceplates Used to hold work too large or shaped so it cannot be held in chuck or between centers Usually equipped with several slots to permit use of bolts to secure work Angle plate used so axis of workpiece may be aligned with lathe centers Counterbalance fastened to faceplate when work mounted off center Prevent imbalance and resultant vibrations 61 Faceplates : Faceplates 62 Faceplates : Faceplates 63 Cutting Speed : Cutting Speed The Peripheral Speed of Workpiece past the Cutting Tool =Cutting Speed D – Diameter (mm) N – Revolutions per Minute (rpm) Feed : Feed f – the distance the tool advances for every rotation of workpiece (mm/rev) Depth of Cut : Depth of Cut perpendicular distance between machined surface and uncut surface of the Workpiece d = (D1 – D2)/2 (mm) Operating Conditions : Operating Conditions Cutting Tool : Cutting Tool 68 Turning Between Centers : Turning Between Centers 69 Some Typical Lathe Jobs : Some Typical Lathe Jobs Turning/Drilling/Grooving/ Threading/Knurling/Facing... Slide 71: Lathe Operations Turning: produce straight, conical, curved, or grooved workpieces Facing: to produce a flat surface at the end of the part or for making face grooves. Boring: to enlarge a hole or cylindrical cavity made by a previous process or to produce circular internal grooves. Drilling: to produce a hole by fixing a drill in the tailstock Threading: to produce external or internal threads Knurling: to produce a regularly shaped roughness on cylindrical surfaces 71 Slide 72: Lathe Operations 72 Turning : Turning Turning .. : Turning .. Cylindrical job Turning .. : Turning .. Excess Material is removed to reduce Diameter Cutting Tool: Turning Tool a depth of cut of 1 mm will reduce diameter by 2 mm Facing : Facing Flat Surface/Reduce length Facing .. : Facing .. machine end of job Flat surface or to Reduce Length of Job Turning Tool Feed: in direction perpendicular to workpiece axis Length of Tool Travel = radius of workpiece Depth of Cut: in direction parallel to workpiece axis Facing .. : Facing .. Eccentric Turning : Eccentric Turning Knurling : Knurling Produce rough textured surface For Decorative and/or Functional Purpose Knurling Tool A Forming Process MRR~0 Knurling : Knurling Knurling .. : Knurling .. Grooving : Grooving Produces a Groove on workpiece Shape of tool shape of groove Carried out using Grooving Tool A form tool Also called Form Turning Grooving .. : Grooving .. Parting : Parting Cutting workpiece into Two Similar to grooving Parting Tool Hogging – tool rides over – at slow feed Coolant use Parting .. : Parting .. Chamfering : Chamfering Chamfering : Chamfering Beveling sharp machined edges Similar to form turning Chamfering tool – 45° To Avoid Sharp Edges Make Assembly Easier Improve Aesthetics Taper Turning : Taper Turning Taper: Taper Turning.. : Taper Turning.. Methods Form Tool Swiveling Compound Rest Taper Turning Attachment Simultaneous Longitudinal and Cross Feeds Conicity Taper Turning ..By Form Tool : Taper Turning ..By Form Tool Taper Turning ,,By Compound Rest : Taper Turning ,,By Compound Rest Slide 93: Cutting Screw Threads Fig : (a) Cutting screw threads on a lathe with a single-point cutting tool. (b) Cutting screw threads with a single-point tool in several passes, normally utilized for large threads. The small arrows in the figures show the direction of feed, and the broken lines show the position of the cutting tool as time progresses. (c) A typical carbide insert and toolholder for cutting screw threads. (d) Cutting internal screw threads with a carbide insert. 93 Types of Screw threads : Types of Screw threads Fig : Various types of screw threads 94 Drilling : Drilling Drill – cutting tool – held in TS – feed from TS Drilling : Drilling Drilling And Drills : Drilling And Drills Drills Have high lenth to diameter ratio Capable of producing deep holes Some what fexable Flutes: two spiral grooves that run the length of the drill and allow the chips to escape Small changes in drill geometry can have a significant effect on the drill’s performance Lathe Accessories : Lathe Accessories Divided into two categories Work-holding, -supporting, and –driving devices Lathe centers, chucks, faceplates Mandrels, steady and follower rests Lathe dogs, drive plates Cutting-tool-holding devices Straight and offset toolholders Threading toolholders, boring bars Turret-type toolposts 98 Lathe Centers : Lathe Centers Work to be turned between centers must have center hole drilled in each end Provides bearing surface Support during cutting Most common have solid Morse taper shank60º centers, steel with carbide tips Care to adjust and lubricate occasionally 99 Lathe Centers : Lathe Centers 100 Revolving Tailstock Centers : Revolving Tailstock Centers Replaced solid dead centers for most machining operations Used to support work held in chuck or when work is being machined between centers Contains antifriction bearings which allow center to revolve with workpiece No lubrication required between center and work Types: revolving dead center, long point center, and changeable point center 101 Revolving Tailstock Centers : Revolving Tailstock Centers 102 Microset Adjustable Center : Microset Adjustable Center Fits into tailstock spindle Provides means of aligning lathe centers or producing slight tapers on work machined between centers Eccentric slide (dovetail) allows center to be adjusted limited amount to each side of center 103 Self-Driving Live Center : Self-Driving Live Center Mounted in headstock spindle Used when entire length of workpiece is being machined in one operation Chuck or lathe dog could not be used to drive work Grooves ground around circumference of lathe center point provide drive Work usually soft material such as aluminum 104 Steadyrest : Steadyrest Used to support long work held in chuck or between lathe centers Prevent springing Located on and aligned by ways of the lathe Positioned at any point along lathe bed Three jaws tipped with plastic, bronze or rollers may be adjusted to support any work diameter with steadyrest capacity 105 Steadyrest : Steadyrest 106 Follower Rest : Follower Rest Mounted on saddle Travels with carriage to prevent work from springing up and away from cutting tool Cutting tool generally positioned just ahead of follower rest Provide smooth bearing surface for two jaws of follower rest 107 Follower Rest : Follower Rest 108 Mandrel : Mandrel Holds internally machined workpiece between centers so further machining operations are concentric with bore Several types, but most common Plain mandrel Expanding mandrel Gang mandrel Stub mandrel 109 Mandrel : Fig : Various types of mandrels to hold workpieces for turning. These mandrels are usually mounted between centers on a lathe. Note that in (a) both the cylindrical and the end faces of the workpiece can be machined, whereas in (b) and (c) only the cylindrical surfaces can be machined. Mandrel 110 Plain Mandrel : Plain Mandrel 111 Expanding Mandrel : Expanding Mandrel 112 Gang Mandrel : Gang Mandrel 113 Stub Mandrel : Stub Mandrel 114 Lathe Dogs : Lathe Dogs Drives work machined between centers Has opening to receive work and setscrew to fasten the dog to work Tail of dog fits into slot on driveplate and provides drive to workpiece Made in variety of sizes and types to suit various workpieces 115 Standard bent-tail lathe dog : Standard bent-tail lathe dog Most commonly used for round workpieces Available with square-head setscrews of headless setscrews 116 Standard bent-tail lathe dog : Standard bent-tail lathe dog Bent tail engages in slot on drive plate 117 Straight-tail lathe dog : Straight-tail lathe dog 118 Driven by stud in driveplate Used in precision turning Safety clamp lathe dog : Safety clamp lathe dog Used to hold variety of work Wide range of adjustment 119 Heavy Duty Lathe Dog : Heavy Duty Lathe Dog 120 Wider range than others Used on all shapes Super Quick-Change Toolpost : Super Quick-Change Toolpost Provides fast, accurate, and reliable method of quickly changing and setting various toolholders for different operations Locking system has two sliding gibs forced out against toolholder Handle pulled into lock position Provides rigid, positive lock with zero backlash 121 Super Quick-Change Toolpost : Super Quick-Change Toolpost 122 Simple formula : Simple formula 123 Slide 124: Simple Problems Problem -1 A mild steel rod having 50 mm diameter and 500 mm length is to be turned on a lathe. Determine the machining time to reduce the rod to 45 mm in one pass when cutting speed is 30 m/min and a feed of 0.7 mm/rev is used. 124 Slide 125: Required spindle speed as: N = 191 rpm Solution Given data: D = 50 mm, Lj = 500 mm v = 30 m/min, f = 0.7 mm/rev Substituting the values of v and D in V = ΠDN/1000 M/min 125 Slide 126: Simple Problems Problem -2 Determine the angle at which the compound rest would be swiveled for cutting a taper on a work piece having a length of 150 mm and outside diameter 80 mm. The smallest diameter on the tapered end of the rod should be 50 mm and the required length of the tapered portion is 80 mm. Solution Given data: D1 = 80 mm, D2 = 50 mm, Lj = 80 mm (with usual notations) tan = (80-50) / 280 or = 10.620 The compound rest should be swiveled at 10.62o 126 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.