Introduction Lathe is a machine, which removes the metal from a piece of work to the required shape &size The basic lathe that was designed to cut cylindrical metal stock has been developed further to produce screw threads. tapered work. Drilled holes. knurled surfaces, and crankshafts. The typical lathe provides a variety of rotating speeds and a means to manually and automatically move the cutting tool into the workpiece.

TYPES OF LATHES Engine Lathe Speed Lathe Bench Lathe Tool Room Lathe Special Purpose Lathe Gap Bed Lathe

Types of Lathe Engine or Center Lathe The most common form of lathe, motor driven and comes in large variety of sizes and shapes. Bench Lathe A bench top model usually of low power used to make precision machine small work pieces. Tracer Lathe A lathe that has the ability to follow a template to copy a shape or contour.

Tool Room Lathe A lathe in which specially equipped for doing accurate work like manufacture of tools, test gauges,dies and similar precision parts. Turret Lathe Lathe which have multiple tools mounted on turret either attached to the tailstock or the cross-slide, which allows for quick changes in tooling and cutting operations. Computer Controlled Lathe A highly automated lathe, where both cutting, loading, tool changing, and part unloading are automatically controlled by computer coding. Special Purpose Lathes These lathe machines are used for applications such as railroad wheels, gun barrel and rolling mill rolls. The size of the workpiece is usually large in these machines.

Component Description

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

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

Magnetic Chucks 9 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

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

Rests Steady Rest Follower Rest

Rests

Parts of Laths Machine 1.Lathe Bed and Ways 2.Headstock 3.Speed Gears 4.Feed Gears 5.Carriage 6.Cross Slide 7.Compound 8.Thread Chasing Dial 9.Tailstock 10.Coolant System

Apron mechanism Apron mechanism is used to move carriage on the lead screw and also for automatic tread cutting operation.

Apron mechanism

Lathe Specifications A lathe is specified by its – Swing – maximum diameter of the workpiece – Distance from headstock and tailstock centers – Length of the bed Lathes are available in a variety of styles and types of construction power Types of lathes – Bench lathe: Placed on a bench Low power Hand feed operated – Tool room lathes: High precision – Engine lathes Available in a wide variety of sizes Used for a variety of turning operations

Cutting Speed  Rate at which point on work circumference travels past cutting tool  Always expressed in feet per minute (ft/min) or meters per minute (m/min)  Important to use correct speed for material Too high: cutting-tool breaks down rapidly Too low: time lost, low production rates

Calculating Lathe Spindle Speed  Given in revolutions per minute  Cutting speed of metal and diameter of work must be known  Proper spindle speed set by dividing CS (in/min) by circumference of work (in)

. Lathe Feed Distance cutting tool advances along length of work for every revolution of the spindle Feed of engine lathe dependent on speed of lead screw for feed rod – Speed controlled by change gears in quick-change gearbox Roughing cut – Purpose to remove excess material quickly – Coarse feed: surface finish not too important.010- to.015-in. (0.25- to 0.4-mm) Finishing cut – Used to bring diameter to size – Fine feed: Produce good finish.003- to.005-in (0.07- to mm

. Depth of Cut Depth of chip taken by cutting tool and one-half total amount removed from workpiece in one cut Only one roughing and one finishing cut – Roughing cut should be deep as possible to reduce diameter to within.030 to.040 in. (0.76 to 1 mm) of size required – Finishing cut should not be less than.005 in.

.. Example: Depth of cut on a lathe

47-23 Factors Determining Depth of Rough-Turning Cut Condition of machine Type and shape of cutting tool used Rigidity of workpiece, machine, and cutting tool Rate of feed

Operations on Lathe Turning Facing knurling Grooving Parting Chamfering Taper turning Drilling Threading

TURNING OPERATION 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 Flat Surface/Reduce length  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 = D/2  Depth of Cut: in direction parallel to workpiece axis

Knurling

Grooving Produces a Groove on workpiece Shape of tool  shape of groove Carried out using Grooving Tool  A form tool Also called Form Turning

Parting Cutting workpiece into Two Similar to grooving Parting Tool tool rides over – at slow feed Coolant use

Chamfering  Beveling sharp machined edges  Similar to form turning  Chamfering tool – 45° Avoid Sharp Edges Make Assembly Easier Improve Aesthetics

Taper Turning Taper:

Taper Turning..By Form Tool

Drilling Drill – cutting tool – held in TS – feed from TS

Thread Cutting.. Carried out Using Thread Cutting Tool There should be Definite Relative Motion Between Tool and Workpiece During Cutting Carriage is moved by Lead Screw Process may require more than One Cut to achieve the depth Threads V Square Pitch – distance moved in 1 revolution

Thread Cutting..