Lathe-Types, Parts, Feed Mechanisms, Specifications,Lathe Accessories and Attachments,Lathe Operations
- 1. 9/10/2014 1 LATHE MACHINE MACHINE TOOLS Machine Tools 2 The Lathe Lathe is a machine tool which holds the work between two rigid and strong supports, called centers, or in a chuck or face plate. The cutting tool is rigidly held and supported in a tool post and is fed against the revolving work. While the work revolves about its own axis, the tool is made to move either parallel to (Cylindrical surface) or at an angle with the axis (Tapered surface) to cut the desired material. IntroductiontoEngineLathe
- 2. 9/10/2014 2 Machine Tools 3 Lathe Basics IntroductiontoEngineLathe Machine Tools 4 Parts of a Lathe • Bed • Head stock • Tailstock • Carriage • Feed mechanism IntroductiontoEngineLathe
- 3. 9/10/2014 3 Machine Tools 5 Lathe Basics Headstock IntroductiontoEngineLathe Machine Tools 6 Lathe Basics Bed IntroductiontoEngineLathe
- 4. 9/10/2014 4 Machine Tools 7 Lathe Basics Carriage/Apron IntroductiontoEngineLathe Machine Tools 8 Lathe Basics Tailstock IntroductiontoEngineLathe
- 5. 9/10/2014 5 Machine Tools 9 Figure: Diagram of an engine lathe, showing its principal components Engine Lathe IntroductiontoEngineLathe Machine Tools 10 Lathe Basics Cross Slide APRON Half Nut Lever 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 Lead Screw IntroductiontoEngineLathe
- 6. 9/10/2014 6 Machine Tools 11 Types of Lathe 1. Speed lathe Simplest of all types of lathe Contains Bed, Headstock, Tailstock, Tool post on adjustable slide No feed box, Lead screw, Carriage Headstock spindle speed:1200 to 3600 rpm Applications: Wood working, spinning, polishing etc. Machine Tools 12 Types of Lathe … 2. Engine or Center lathe Most widely used Early lathes were driven by steam engines and so the name engine lathe Heavy duty Head stock is much more robust in construction Contains additional mechanism for multiple speeds Carriage, Feed rod and Lead screw are available and hence, longitudinal and cross feeds are possible
- 7. 9/10/2014 7 Machine Tools 13 Types of Lathe … 3. Bench lathe Small lathe, mounted on a bench Just a scaled version of engine lathe Used for small and precision work 4. Tool room lathe Greater accuracy More versatility Wide range of speeds and feeds Applications: Precision work on tools, dies, gauges Machine Tools 14 Capstan and Turret Lathes Tailstock of an engine lathe is replaced by a hexagonal turret Several tools fitted on the turret are fed into work in proper sequence to carryout different operations in one setting Hence used for production work Capstan lathe Turret with its saddle can move for a short distance over the sub bed. Limitation: Length of a job to be machined is limited Turret lathe: Turret with its saddle slides directly on bed-ways enabling longer work to be machined
- 8. 9/10/2014 8 Machine Tools 15 Types of Lathe … 6. Special purpose lathes Used for special purposes Wheel lathe: For finishing journals, turning locomotive wheels Gap-bed lathe: A section of bed adjacent to tailstock is removable thereby allowing very large diameter work to swing Duplicating lathe: To duplicate the shape of a template on to a workpiece Wheel lathe Duplicating lathe Machine Tools 16 Types of Lathe … 7. Automatic lathe Automatic control: Once the tools are set and the machine starts, all the operations will be performed automatically Change of tools, speeds and feeds are done automatically The jobs are made continuously one after the other without the intervention of operation High speed, Heavy duty and Mass production lathe Single or multi spindle Capable of simultaneous cuts Operator’s role: Loading the bar stock Setting the tools Machine maintenance
- 9. 9/10/2014 9 Machine Tools 17 Types of Lathe … 7. CNC lathe Computer Numerical Control Wide variety of process capability Multiple axes Indexing and contouring head On-line and off-line programming available Equipped with one or more turrets Each turret is equipped with a variety of tools Machine Tools 18 The Bed • Rigid to withstand the cutting forces • Massive, sufficient to absorb vibration • Resist the torsional stresses set up. • Should be seasoned naturally to avoid distortion. Diagonal ribs Lathe
- 10. 9/10/2014 10 Machine Tools 19 The Headstock • Headstock spindle • Cone Pulley • Backgears and backgear lever • Gear Box • Live center Main of parts of headstock are: Lathe Machine Tools 20 The Headstock Spindle 1. Threaded end 2. Taper sleeve 3. Live center 4. Threaded nose 5. Spindle hole Lathe
- 11. 9/10/2014 11 Machine Tools 21 The Headstock • Need for speed change –Workpiece material –Cutting tool material –Type of operation –Workpiece size –Surface finish –Cutting fluid –Rigidity of machine tool Lathe Machine Tools 22 Methods to vary the speeds 1. By belt drive on cone pulley fitted on the headstock spindle with or without a back gear arrangement. 2. By all gear drive using sliding gears or clutches. 3. By variable speed motor. Lathe
- 12. 9/10/2014 12 Machine Tools 23 Belt Driven Backgeared Headstock In a belt driven back geared headstock, multiple speeds can be obtained 1. Direct speed or back gear out 2. Indirect speed or back gear in Spindle Cone Pulley Countershaft Cone Pulley Lathe Machine Tools 24 Speed Ratios • Direct speeds: Spindle speed = • Indirect speeds: Spindle speed = Back gear ratio = Lathe
- 13. 9/10/2014 13 Machine Tools 25 Geared Headstock 15 – splined headstock spindle. Fig.9speedall-gearedheadstock Speed distribution, r (GP Ratio) 1 – Fast Pulley 2 – Loose pulley 3 – Spindle shaft 4 to 13 – gears with Z4 to Z13 teeth 10 – Intermediate shaft 14 – Gear box casting Preferred values for ‘r’, = 1.12, 1.25, 1.4, 1.6 and 2 Lathe Machine Tools 26 Tailstock Lathe
- 14. 9/10/2014 14 Machine Tools 27 Carriage Lathe Machine Tools 28 Single Screw Tool post 5 – concave ring Fig.: Single screw tool post 1 – screw 2 – body 3 – tool 4 – convex rocker Lathe
- 15. 9/10/2014 15 Machine Tools 29 Four way Tool post Figure: Four way Tool post 1 – clamping handle 2 – central locking bolt 3 – set screws 4 – tool Lathe Machine Tools 30 Feed Mechanism • Feed: The distance advanced by the tool into or along the workpiece for each revolution of the work. Units: mm/rev. or mm/min. • Types – Longitudinal feed (cylindrical turning, thread cutting, etc.) – Cross feed (facing, parting, etc.) – Angular feed (taper turning, chamfering, etc.) Lathe
- 16. 9/10/2014 16 Machine Tools 31 PowerTrain End of bed gearing Changegear train Feedrod& leadscrew Apron Mechanism Tumbler gear feed reverse mechanism Bevel gear feed reverse mechanism Feed gear box 1. Sliding gear mechanism 2. Sliding clutch mechanism 3. Gear cone and Norton feed gear 4. Sliding key mechanism 5. Combination of two or more of 1, 2, 3, 4 Feed Mechanism Lathe Clutch handle Figure: Layout diagram of feed drive Tumbler gear Change Gears Norton Gears Sliding Key Mechanism Feed Mechanisms … Headstock spindle Sliding key operating handle Lead screw Feed rod
- 17. 9/10/2014 17 Feed Reverse Mechanism using Tumbler Gears Tumbler gears are used to give the desired direction of movement to the lathe carriage, via lead screw or feed rod. Tumbler Gear Mechanism Tumbler Gears Forward motion: A-B-D: Carriage moves towards headstock Reverse motion: A-C-B-D: Carriage moves away from headstock Drawback: Non-rigid construction, hence not suitable for heavy duty Two pinions B and C are mounted on a bracket.
- 18. 9/10/2014 18 Feed Reverse Mechanism using Bevel Gear Mechanism Constructional details 1 – headstock spindle 2 – spindle gear 3 – driver gear keyed to stud shaft (7) 5 – gear on the lead screw (6) 8, 10, 12 – bevel gears with equal no. of teeth 11 – clutch (keyed to stud 7 by a feather key) 9 – lever (to engage clutch to gear 8 or 10 or keep in neutral position) (Gear 13-sleeve-bevel gear 8) rotate freely on stud 7 as one unit bevel gear 10 also rotates freely on stud 7 The clutch operated bevel gear feed reversing mechanism incorporated below the headstock or in the apron provides sufficient rigidity in construction. Operation: When clutch is engaged to bevel gear 8: Motion flow: gear 2 – Idler gear – (gear 13, sleeve, bevel gear 8) – (stud 7, gear 3) Result: Gear 3 rotates in the same direction as that of gear 2. Hence, Forward motion, Carriage moves towards headstock. When clutch is engage to gear 10: Motion flow: gear 2 – Idler – (gear 13, sleeve, bevel gear 8) – bevel gear 12 – bevel gear 10 – (stud 7, gear 3) Result: Gear 3 rotates in opposite direction to that of gear 2. Hence, Reverse motion, Carriage moves away from headstock. Feed Reverse Mechanism … using Bevel Gear Mechanism
- 19. 9/10/2014 19 Feed Mechanisms … Figure: Layout diagram of feed drive Change Gears Change gears are used in thread cutting to give proper relative motion between the work and tool Change Gear Mechanism Figure: Change gears Change Gears E G
- 20. 9/10/2014 20 Feed Mechanisms … Figure: Layout diagram of feed drive Norton Feed Gears Norton Feed Gears
- 21. 9/10/2014 21 Feed Mechanisms … Figure: Layout diagram of feed drive Sliding Key Mechanism Sliding Key Mechanism I – driving shaft; II – driven shaft 1 – sliding key operating handle 2 – sliding rod 3 – lever spring 3 I II It consists of a cone of gears mounted on a hollow shaft. Gears rotate independently freely on the shaft. Steel washers are placed between the gears to prevent simultaneous engagement of adjacent gears. With the help of sliding key (that slides within the hollow shaft), any one of the gears may be engaged to the cone gears on the driven shaft. Motion is then transmitted finally to the lead screw or feed rod.
- 22. 9/10/2014 22 Apron Mechanism 1 – lead screw; 2- feed rod 3 – half-nut; 4 – cross feed screw 5, 6, 7 – Gear train for cross feed 9 – cone clutch for longitudinal feed 10, 11 – gear train for long. feed. 12 – gear for hand wheel 13 – pinion; 14 – apron 15 – rack; 16 – hand wheel 17 – knob for longitudinal feed 18 – cone clutch for cross feed 19 – knob for cross feed 20 – lever; 21 – cam 22 – sliding gear 23 – gear on worm shaft 24 – worm; 25 – cam plate 26 – half nut operating handle Apron Mechanism
- 23. 9/10/2014 23 Feed Rod & Lead Screw lead screw feed rod Feed rod Used to engage automatic tool feed during turning, boring, facing etc. Automatic tool feed is obtained by engaging feed rod so as to transmit power from the lathe spindle to the apron gears Lead screw: Long threaded master screw Engaged during thread cutting operation In lathes without feed rod, lead screw may be used for turning, boring etc. Split Half Nut Mechanism 1 – cam slot; 2 – frame; 3 – lead screw; 4 – hand lever; 5 – pin; 6 – circular plate; 7 – half nuts Fig. b) Sectional views of Half Nut Mechanism Half Nut is engaged to the lead screw during threading. The nut is made in two halves. Each of these halves carries a pin at the back (P1 and P2 as shown in Fig. a) which engages into the cam slots provided in a plate at their back. When this plate is rotated by means of the lever L, it engages or disengages the split half nut with the lead screw depending upon the direction of rotation of the lever. Fig. a) Half nut
- 24. 9/10/2014 24 Machine Tools 47 Kinematic Structure of a Lathe Lathe Machine Tools 48 Specifications of a Lathe A = Length between centers B = Swing over gap (Gap bed lathes) C = Height of centers D = Swing over carriage E = Swing over bed IntroductiontoEngineLathe
- 25. 9/10/2014 25 Machine Tools 49 Turning Operation FIGURE : Schematic illustration of a turning operation showing depth of cut, d, and feed, f. cutting speed is the surface speed of the workpiece at the tool tip. IntroductiontoEngineLathe Machine Tools 50 Lathe Operations Fig: Various cutting operations that can be performed on a lathe. IntroductiontoEngineLathe
- 26. 9/10/2014 26 Machine Tools 51 Lathe Operations Fig: Various cutting operations that can be performed on a lathe. IntroductiontoEngineLathe Machine Tools 52 Accessories&Attachments Lathe – Accessories & Attachments Accessories Devices employed for holding and supporting the work and the tool. Attachments Devices to increase production and efficiency and widen its scope of use.
- 27. 9/10/2014 27 Machine Tools 53 Lathe – Accessories & Attachments Accessories Centers Face & Angle Plates Dogs or Carriers Chucks Mandrels Rests Attachments Bar Stops Thread Chasing Dials Taper turning Milling Grinding Gear Cutting Hydro-copying Accessories&Attachments Machine Tools 54 Centers A – Ordinary Center E – Tipped (brazed) Center B – Ball Center F – Insert type Center D – Half Center H – Use of half center 1 – Half center 2 – Facing tool G - Pipe Center C – Frictionless Center 1 – Insert type center 2 – Nut 3 – Roller bearing 4 – Thrust bearing 5 - Housing Accessories&Attachments
- 28. 9/10/2014 28 Machine Tools 55 Driving Plates and Dogs Fig: Eccentric Turning Fig. Straight dog Boss Threaded Hole Projected Pin Fig: Driving Plate Accessories&Attachments Machine Tools 56 Holding the work between Centers Fig.: mounting the work between centers using a "dog” Accessories&Attachments
- 29. 9/10/2014 29 Machine Tools 57 Chuck Fig: Four Jaw Chuck 1- concentric circle; 2 – chuck body; 3 – Jaw screw; 4 – jaw; 5 – gripping surface; 6 – recess for back plate. Accessories&Attachments Machine Tools 58 Chuck Fig: Three Jaw Chuck Accessories&Attachments
- 30. 9/10/2014 30 Machine Tools 59 Chuck Fig: Magnetic Chuck 1-work; 2-magnetic material; 3-keepers; 4-face plates, 5-magnet Fig: Hydraulic Chuck 1-cylinder; 2-air passage; 3-head stock spindle; 4-piston; 5-valves;; 6-piston rod; 7-link; 8-jaw; 9-guide; 10-sliding unit Accessories&Attachments Machine Tools 60 Collet 1-Bearing; 2-Spindle; 3-Nut; 4-Key; 5-Chuck; 6-Collet Fig: Collet Chuck Accessories&Attachments
- 31. 9/10/2014 31 Machine Tools 61 Collet Fig.: collet Accessories&Attachments Machine Tools 62 Face Plate & Angle Plate Clamping Plate Balance Weight Packing Work Fig: Face Plate Fig: Angle Plate 1-face plate; 2-balance weight; 3-elbow pipe; 4-clamping nut; 5-angle plate; 6-clamping nut Accessories&Attachments
- 32. 9/10/2014 32 Machine Tools 63 Face Plate Fig.: face plate for non-cylindrical workparts Accessories&Attachments Machine Tools 64 Mandrels Plain Mandrel Step Mandrel Threaded Mandrel Collar Mandrel Accessories&Attachments
- 33. 9/10/2014 33 Machine Tools 65 Mandrels Fig: Cone Mandrel 1-solid cone; 2-sliding cone; 3-nut Fig: Gang Mandrel 1-fixed collar; 2-hollow workpieces; 3-movable collar; 4-nut Fig: Expansion Mandrel 1-sleeve; 2-tapered pin Accessories&Attachments Machine Tools 66 Steady Rest Accessories&Attachments
- 34. 9/10/2014 34 Machine Tools 67 Follower Rest Fig.: Follower rest Accessories&Attachments Machine Tools 68 Thread Cutting - Terminology Fig. Elements of external threads Accessories&Attachments
- 35. 9/10/2014 35 Machine Tools 69 Thread Cutting - Terminology Fig. Single Start Fig. Double Start Fig. Triple Start . Accessories&Attachments Machine Tools 70 Thread Cutting Fig: General set-up of lathe for screw cutting Accessories&Attachments
- 36. 9/10/2014 36 Machine Tools 71 Thread Cutting - Change Gear Ratio , Accessories&Attachments Machine Tools 72 Cutting metric thread on British standard lead screws or Vice Versa To cut metric threads on lathes having British standard lead screw: To cut British standard threads to be cut on a lathe having lead screw of metric pitch: 5 127 127 5 Accessories&Attachments
- 37. 9/10/2014 37 Machine Tools 73 Cutting R.H. and L.H. Threads Right Hand threads: Threads slope up to the right when screw is held vertically. The spindle and the lead screw will rotate in the same direction. Left Hand threads: Threads slope up to the left when screw is held vertically. The spindle and the lead screw will rotate in opposite direction. This change of direction of rotation on lathe is effected by tumbler gear or by using proper number of idlers. Accessories&Attachments Machine Tools 74 Thread Cutting - Gear Trains Simple gear train Compound gear train Often lathes are equipped with a set of gears ranging from 20T to 120T in steps of 5T. In addition, a gear of 127 teeth is also provided which is known as translating gear. Accessories&Attachments
- 38. 9/10/2014 38 Machine Tools 75 Left Hand thread - Applications Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten, e.g. on a left-hand bicycle pedal. In combination with right-handed threads in turnbuckles. In Gold ornaments, e.g. ear studs. In some gas supply connections to prevent dangerous misconnections, for example in gas welding the flammable gas supply uses left- handed threads. RH ThreaLH Thread Accessories&Attachments Machine Tools 76 Examples: 2 6 1 3 1 3 20 20 20 60 Simple train with one idlerSimple train with one idler 1 3 25 25 25 75 Simple train with one idlerSimple train with one idler 1 3 30 30 30 90 Simple train with one idlerSimple train with one idler Calculate change gears for cutting R.H. threads of 2 mm pitch on a lathe having lead screw of 6 mm pitch. Pb.: Soln: Accessories&Attachments
- 39. 9/10/2014 39 Machine Tools 77 Examples: Calculate change gears for cutting L.H. threads of 1.5 mm pitch on a lathe having lead screw of 6 mm pitch. Pb.: Soln: 1.5 6 1 4 1 4 20 20 20 80 Simple train with one idlerSimple train with one idler 1 4 25 25 20 100 Simple train with one idlerSimple train with one idler Accessories&Attachments Machine Tools 78 Examples: Calculate change gears for cutting R.H.B.S.W. “V” threads of 12 TPI on a lathe having lead screw of 8 TPI. 1 12⁄ 1 8⁄ 2 3 20 20 20 60 Simple train with one idlerSimple train with one idler 2 3 25 25 25 75 Simple train with one idlerSimple train with one idler 8 12 2 3 Pb.: Soln: Accessories&Attachments
- 40. 9/10/2014 40 Machine Tools 79 Examples: Calculate change gears for cutting R.H. threads of 1 mm pitch on a lathe having lead screw of 8 mm pitch. 1 8 1 8 20 20 20 160 Compound Gear train with no idler Gear A = 20 Gear B = 80 Gear C=30 Gear D = 60 Compound Gear train with no idler Gear A = 20 Gear B = 80 Gear C=30 Gear D = 60 1 8 1 4 2 1 4 1 2 1 4 20 20 1 2 30 30 20 80 30 60 Pb.: Soln: Accessories&Attachments Machine Tools 80 Examples: Calculate change gears to cut R.H. threads of 25 TPI on a lathe having lead screw of 6 TPI. Pb.: Soln: 6 25 6 25 2 3 5 5 2 5 20 20 3 5 15 15 40 100 45 75 Compound Gear train with no idler Gear A = 40 Gear B = 100 Gear C = 45 Gear D = 75 Compound Gear train with no idler Gear A = 40 Gear B = 100 Gear C = 45 Gear D = 75 Accessories&Attachments
- 41. 9/10/2014 41 Machine Tools 81 Examples: Calculate change gears to cut L.H. single start threads of 0.25” pitch on a lathe having lead screw of 8 mm lead. Compound Gear train with one idler Gear A = 127 Gear B = 80 Gear C = 50 Gear D = 100 Compound Gear train with one idler Gear A = 127 Gear B = 80 Gear C = 50 Gear D = 100 0.25" 1 4 127 5 1 4⁄ 8 127 5 32 127 5 16 2 ⇒ 127 80 1 50 2 50 127 50 80 100 Pb.: Soln: Accessories&Attachments Machine Tools 82 Setting of Tools for Threading Fig. Setting threading tool for external threading Fig. Setting threading tool for internal threading Accessories&Attachments
- 42. 9/10/2014 42 Machine Tools 83 Feeding the Tool in Threading Fig: Straight Thread Fig: Inclined feed Fig: Inclined feed using a form tool Accessories&Attachments Machine Tools 84 Fig.: Cutting a screw thread on a lathe Inset shows face of threading dial Thread Cutting Accessories&Attachments
- 43. 9/10/2014 43 Machine Tools 85 Providing undercut Fig.: Under Cut Accessories&Attachments Machine Tools 86 Cutting Square and Acme Threads Fig. Tool setting for square threads nceCircumfere threadofLead .. tan Accessories&Attachments
- 44. 9/10/2014 44 Machine Tools 87 Fig.: Threading cycle to produce threads Thread Cutting Cycle Accessories&Attachments Machine Tools 88 Thread Chasing Dial Fig: Thread Chasing Dial Accessories&Attachments
- 45. 9/10/2014 45 Machine Tools 89 Taper Turning 1 100 1 100 tan 2⁄ 2 Accessories&Attachments Machine Tools 90 Tail Stock Set-over Method Let, H = set-over required D = larger diameter d = smaller diameter L = total length of work l = length of taper (all dimensions in ‘mm’) sin α is very small and hence, sin tan tan 2 But, ∴ 2 Accessories&Attachments
- 46. 9/10/2014 46 Machine Tools 91 Swiveling the Compound Rest Fig. Turning taper by swiveling the compound rest Accessories&Attachments Machine Tools 92 Taper turning attachment Fig. Use of taper turning attachment Accessories&Attachments
- 47. 9/10/2014 47 Machine Tools 93 Form or Broad Nose Tool Fig. Turning short taper by a form (broad nose) tool Accessories&Attachments Machine Tools 94 Machining Time Calculations in Turning Cutting speed: where d = diameter of the work in mm; N = speed of the work in rpm. Feed: mm / rev. or mm / min. f (mm / min) = f (mm / rev) X N (rev / min) Machining time: where l = length of the job, mm f = feed in mm/rev.; N = speed in rpm. 1000 / Accessories&Attachments
- 48. 9/10/2014 48 Machine Tools 95 References TextBooks • Materials and Processes in Manufacturing, by E. Paul DeGarmo, et al, Wiley • Manufacturing Engineering and Technology, by S Kalpakjian and Steven R Schmid, Pearson • Machining Technology – Machine Tools and Operations, by Helmi A Youssef and Hassan El-Hofy, CRC Press • Manufacturing Science, by A Ghosh and AK Mallik, EWP • Machining & Machine Tools, by AB Chattopadhyay, Wiley