lathe ppt

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Central Lathe Machine

• Lathe is a machine in which work piece is held and rotated on its axis while cutting tool is advanced along the line of desired cut.

• Lathe was the first machine tool which came into being as a useful machine for metal cutting.

• Lathe is a machine, which removes the metal from a piece of work to the required shape &size

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Definition

Working Principle

• Workpiece revolves about its own axis , the tool is made to move in parallel or at an inclination with the axis of a material to be cut.

• The material from the workpiece is removed in the form of chips.

• Too cut the material properly , the tool material should be harder than the workpiece material.

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Working Principle

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Types of Lathe• Bench Lathe• Speed Lathe• Engine Lathe Belt drive lathe Individual motor drive lathe Gear head lathe• Tool room lathe• Capstan and Turret lathe• Automatic lathe• Special purpose lathe Wheel lathe Gap bed lathe Duplicating lathe T - lathe

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Bench Lathe

• Very small lathe and usually mounted on a bench or cabinet.• Very accurate , hence used for small and precision work.• Provided with all the attachments, which a larger lathe can do.

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Speed Lathe

• Simplest of all types of lathe.• Their spindle rotates at very high speed ranging from 1200 to 3600 rpm.• No provision for gear box, carriage and lead screw.• Tool is controlled by hand, depth of cut and chip thickness are very small.

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Engine Lathe

• It is most widely used and it is an important type of lathe.• The term engine is associated because earlier lathes were driven by steam engines.• A lathe which receives its power from an over-head line shaft is known as belt-driven

lathe.• A lathe which receives its power from an individual motor which is integral with the

machine is known as motor driven lathe.• A lathe which receives its power from a constant speed motor and all speed changes, are obtained by shifting various gears which are located in the headstock, is known as gear-head lathe.

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Tool room Lathe

• Similar as engine lathe.• Spindle speeds ranging from very low to high speed i.e. upto 2500 r.p.m.• Used for precision work on tools, dies, gauges and in machining work, where accuracy

is required.• But are more expensive.

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Capstan & Turret Lathe

• Used in mass production.• The tailstock of an engine lathe is replaced by a hexagonal turret.• Without resetting of workpiece and tools, several different operations can be done on

the workpiece.

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Automatic Lathe

• High speed, heavy duty and mass production lathes.• Whole jobs are done automatically.• After the job is complete, without attention of an operator, the machine will continue to

repeat the cycles and produce identical parts.

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Specifications of Lathe

• The length of bed : It indicates the approximate floor space

occupied by the lathe.• The length between centres : It is the maximum length of work that

can be mounted between the lathe centres.

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Specifications of Lathe• The height of centres from the bed : It is the distance between top surface of the bed and the imaginary center line passing through live centre and dead centre.• The maximum bar diameter : It is the maximum diameter of work that will pass through the hole of the head stock spindle.• The swing diameter of work over bed : It is the largest diameter of

work that will revolve without touching the bed. It is twice the height of the centres from the bed.

• The swing diameter of work over the carriage : It is the largest diameter of work that will revolve over the lathe saddle. It is smaller than the swing diameter over bed.

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BED

SWING DIAMETER OVER BED

HEIGHT OF CENTRE FROM BED

SWING DIAMETER OVER CARRIAGE

CARRIAGE

Lathe Size

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Lathe Size

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Lathe Size

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Lathe Size

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Component Description

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Main Parts

• Bed• Headstock• Feed and lead screws• Carriage• Tailstock

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Lathe Bed

• Heavy, rugged casting

• Made to support working parts of lathe

• On top section are machined ways

• Guide and align major parts of lathe

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Lathe Bed

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Headstock

• Clamped on left-hand end of bed• Headstock spindle

• Hollow cylindrical shaft supported by bearings• Provides drive through gears to work-holding

devices• Live center, faceplate, or chuck fitted to spindle nose

to hold and drive work• Driven by stepped pulley or transmission gears• Feed reverse lever

• Reverses rotation of feed rod and lead screw

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Headstock

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Headstock

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Back Gear arrangementBack Gear arrangement

Headstock belt driveHeadstock belt drive

Quick-Change Gearbox

• Contains number of different-size gears• Provides feed rod and lead-screw with

various speeds for turning and thread-cutting operations• Feed rod advances carriage when

automatic feed lever engaged• Lead screw advances the carriage for

thread-cutting operations when split-nut lever engaged

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Quick-Change Gearbox

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Carriage

• Used to move cutting tool along lathe bed• Consists of three main parts

• Saddle• H-shaped casting mounted on top of lathe

ways, provides means of mounting cross-slide and apron

• Cross-slide• Apron

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Carriage

< Saddle

< Apron

Carriage

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Carriage

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ApronApron

• The apron attached to the front of the carriage, holds most of the control levers. These include the levers, which engage and reverse the feed lengthwise (Z-axis) or crosswise (X-axis) and the lever which engages the threading gears.

• The apron is fastened to the saddle, houses the gears and mechanisms required to move the carriage and cross-slide automatically.

• The apron hand wheel can be turned manually to move the carriage along the Lathe bed. This hand wheel is connected to a gear that meshes in a rack fastened to the Lathe bed.

• The automatic feed lever engages a clutch that provides the automatic feed to the carriage

Cross-slide

• Mounted on top of saddle• Provides manual or automatic cross

movement for cutting tool• Compound rest (fitted on top of cross-slide)

• Used to support cutting tool• Swiveled to any angle for taper-turning• Has graduated collar that ensure accurate

cutting-tool settings (.001 in.) (also cross-slide)

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Cross-slide

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Top Slide (Compound slide)

• Fitted to top of Cross slide• Carries tool post and cutting tool• Can rotate to any angle• Is used to turn tapers

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Tailstock

• Upper and lower tailstock castings• Adjusted for taper or parallel turning by two

screws set in base• Tailstock clamp locks tailstock in any position

along bed of lathe• Tailstock spindle has internal taper to receive

dead center• Provides support for right-hand end of work

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Tailstock

Supports long workpieces when machining.

60 degree 60 degree rotating rotating center center point.point.

Drill Drill ChuckChuck

Turn the Turn the tailstock tailstock handwhehandwheel to el to advance advance the ram.the ram.

Tailstock

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Feed of an Engine Lathe• Distance carriage will travel in one revolution

of spindle• Depends on speed of feed rod or lead screw

• Controlled by change gears in quick-change gearbox

• Obtains drive from headstock spindle through end gear train

• Chart mounted on front of quick-change gearbox indicates various feeds

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Back Gear Mechanism

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Tumbler Gear Mechanism

Feed of an Engine Lathe

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Quick change gear box

Feed of an Engine Lathe

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Lead Screw and Feed Rod

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< Lead Screw< Feed Rod

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Quick change gear box

Lathe Accessories

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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

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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

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Lathe Centers

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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

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Revolving Tailstock Centers

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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

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Self-Driving Live Center

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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

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Three-jaw Universal Chuck

• Holds round and hexagonal work• Grasps work quickly and accurate

within few thousandths/inch• Three jaws move simultaneously when

adjusted by chuck wrench• Caused by scroll plate into which all three

jaws fit

• Two sets of jaw: outside chucking and inside chucking

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Three-jaw Universal Chuck

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Three jaw self centering chuck

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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

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Four-Jaw Independent Chucks

Four-Jaw Independent Chucks

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• With the four jaw chuck, each jaw can be adjusted independently by rotation of the radially mounted threaded screws.

• Although accurate mounting of a workpiece can be time consuming, a four-jaw chuck is often necessary for non-cylindrical workpieces.

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Headstock Spindle Types1. Threaded spindle nose

• Screws on in a clockwise direction

2. Tapered spindle nose• Held by lock nut that tightens on chuck

3. Cam-lock spindle nose• Held by tightening cam-locks using T-

wrench• Chuck aligned by taper on spindle nose

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Threaded Spindle Nose

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Tapered Spindle Nose

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Cam Lock Spindle Nose

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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

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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

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Jacobs Collet Chuck

• Jacobs collet chuck• Utilizes impact-tightening handwheel to

close collets• Wider range than spring-collet chuck

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Jacobs Collet Chuck

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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

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Magnetic Chucks

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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

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Faceplates

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Faceplates

Catch Plate

• Also known as driving plate.• Plain disc of cast iron or steel.• Carries a hole to accommodate a pin which engages with the tail of the lathe carrier.

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Angle Plate• L shaped cast iron plate with two faces.• Carries slots for clamping on the face plate.• Holes and slots are provided on both

faces so that it may be clamped on

the face plate and can hold the

workpiece on the other face by

clamps and bolts.

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Mandrels

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• 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

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Mandrels to Hold Workpieces for Turning

Figure 23.8 Various types of mandrels to hold workpieces for turning. These mandrels usually are 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.

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Plain Mandrel

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Expanding Mandrel

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Gang Mandrel

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Stub Mandrel

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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

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Steadyrest

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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

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Follower Rest

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• For accurate turning operations or in cases where the long work surface is not truly cylindrical, the workpiece can be turned between centers.

• Initially the workpiece has a conical center hole drilled at each end to provide location for the lathe centers.

• Before supporting the workpiece between the centers (one in the headstock and one in the tailstock), a clamping device called a ‘dog’ is secured to the workpiece.

• The dog is arranged so that the tip is inserted into a slot in the drive plate mounted on the main spindle, ensuring that the workpiece will rotate with the spindle.

Work holding between CentersWork holding between Centers

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•Lathe centers support the workpiece between the headstock and the tailstock.

• The center used in the headstock spindle is called the ‘live’ center. It rotates with the headstock spindle.

•The ‘dead’ center is located in the tailstock spindle. This center usually does not rotate and must be hardened and lubricated to withstand the wear of the revolving work.

•The workpiece must have perfectly drilled and countersunk holes to receive the centers.

•The center must have a 60-degree point.


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For accurate machining, cylindrical parts can be turned between centers.

Hardened “dead” centers are mounted in the tailstock; they do not rotate with the workpiece and must be lubricated.

Hardened “live” centers are mounted in the tailstock; they rotate with the workpiece and do not need lubricatio


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Cutting-Off (Parting) Tools• Used when work must be grooved or

parted off• Long, thin cutting-off blade locked

securely in toolholder by either cam lock or locking nut

• Three types of parting toolholders• Left-hand• Right-hand• Straight

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Threading Toolholder

• Designed to hold special form-relieved thread-cutting tool

• Has accurately ground 60º angle• Maintained throughout life of tool

• Only top of cutting surface sharpened when becomes dull

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Styles of Boring Toolholders• Held in standard toolpost

• Light boring toolholder• Used for small holes and light cuts

• Medium boring toolholder• Suitable for heavier cuts• May be held at 45º or 90º to axis of bar

• Mounted on compound rest of lathe• Heavy-duty boring bar holder

• Three bars of different diameters• May be held at 45º or 90º to axis of bar

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Compound Rest Tooling Systems• Standard, or round, toolpost

• Generally supplied with conventional engine lathe

• Fits into T-slot of compound rest• Provides means of holding and adjusting

type of toolholder or cutting tool required• Concave ring and the wedge or rocker

provide for adjustment of cutting-tool height

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Lathe Cutting OperationsFigure 23.1 Miscellaneous cutting operations that can be performed on a lathe. Note that all parts are circular – a property known as axisymmetry. The tools used, their shape, and the processing parameters are described throughout this chapter.

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Turning Operation

Figure 23.3 Schematic illustration of the basic turning operation, showing depth-of-cut, d; feed, f; and spindle rotational speed, N in rev/min. Cutting speed is the surface speed of the workpiece at the tool tip.

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Designations for a Right-Hand Cutting Tool

Figure 23.4 Designations for a right-hand cutting tool. Right-hand means the tool travels form right to left, as shown in Fig. 23.3.

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Right-hand Cutting Tool and Insert

Figure 21.20 (a) Schematic illustration of right-hand cutting tool. The various angles on these tools and their effects on machining are described in Section 23.3.1 Although these tools traditionally have been produced from solid tool-steel bars, they have been replaced largely with (b) inserts made of carbides and other materials of various shapes and sizes.

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Three Important Elements Rotating Speed

It expresses with the number of rotations (rpm) of the chuck of a lathe. When the rotating speed is high, processing speed becomes quick, and a processing surface is finely finished. However, since a little operation mistakes may lead to the serious accident, it is better to set low rotating speed at the first stage.

Cutting DepthThe cutting depth of the tool affects to the processing speed and the roughness of surface. When the cutting depth is big, the processing speed becomes quick, but the surface temperature becomes high, and it has rough surface. Moreover, a life of byte also becomes short. If you do not know a suitable cutting depth, it is better to set to small value.

Feed (Sending Speed )The sending speed of the tool also affects to the processing speed and the roughness of surface. When the sending speed is high, the processing speed becomes quick. When the sending speed is low, the surface is finished beautiful. There are 'manual sending' which turns and operates a handle, and 'automatic sending' which advances a byte automatically. A beginner must use the manual sending. Because serious accidents may be caused, such as touching the rotating chuck around the byte in automatic sending,.

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Turning • Turning is a metal cutting process used for the generation of

cylindrical surfaces.

• Normally the workpiece is rotated on a spindle and the tool is fed into it radially, axially, or both ways simultaneously, to give the required surface.

• The term ‘turning’, in the general sense, refers to the generation of any cylindrical surface with a single point tool.

• Turning is the most commonly used operation in Lathe. By turning operation excess material from the work piece is removed to produce a cylindrical or cone shaped surface.

• Two of the common types of turning are: Straight turning and taper turning.

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•In this operation the work is held in the spindle and is rotated whole the tool is fed past the work piece in a direction parallel to the axis of rotation. •The surface generated is a cylindrical surface.

Straight turningStraight turning

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Other related lathe operationsOther related lathe operations

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Facing: Facing is an operation for generating flat surface at the ends of a work piece. In this operation the feed given is in a direction perpendicular to the axis of rotation.• First, clamp the part securely in a lathe chuck. • Then, install a facing tool• Bring the tool approximately into position, but slightly off of the part.• Always turn the spindle by hand before turning it on. This ensures that no parts

interfere with the rotation of the spindle. • Move the tool outside the part and adjust the saddle to take the desired depth of

cut. • Then, feed the tool across the face with the cross slide. • After facing, there is a very sharp edge on the part. Break the edge with a file.


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Facing

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Shouldering

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Parting

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Thread Cutting

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Drilling

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Boring

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• Chamfering: It is a operation of beveling the extreme end of a work piece. This done to remove unwanted metal projections at the ends and to protect end of the work piece from being damaged and to have a better look.

• Knurling: Knurling is process of embossing a diamond shaped pattern on the surface of the work piece. The purpose of knurling is to provide an effective gripping surface on a work piece to prevent it from slipping when operated by hand. Knurling is done with a special tool called knurling tool. This tool consists of a set of hardened steel rollers in a holder with teeth cut on their surface in definite pattern.


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• Grooving or Recessing Operations: Grooving or recessing operations is the operation of reducing the diameter of a workpiece over a very narrow surface. Grooving or recessing operations, sometimes also called necking operations, are often done on workpiece shoulders to ensure the correct fit for mating parts.

• Drilling/reaming/ Boring: These are operations to accurately make holes on a workpiece. These operations uses the tailstock of the lathe. The tool is held on the tailstock and is fed toward the rotating work piece.


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Other related lathe operationsParting: In. this operation a flat nose tool is used to cut the work piece, with feed in the direction perpendicular to the axis of rotation. A parting tool is deeper and narrower than a turning tool. It is designed for making narrow grooves and for cutting off parts. When a parting tool is installed, ensure that it hangs over the tool holder enough that the holder will clear the workpiece (but no more than that). Ensure that the parting tool is perpendicular to the axis of rotation and that the tip is the same height as the center of the part. A good way to do this is to hold the tool against the face of the part. Set the height of the tool, lay it flat against the face of the part, then lock the tool in place. When the cut is deep, the side of the part can rub against sides of the groove, so it's especially important to apply cutting fluid. In this clip, a part is cut off from a piece of stock.

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•A taper may be defined as a uniform increase or decrease in diameter of a work piece measured along its length. •In a Lathe taper turning is an operation to produce a conical surface by gradual reduction in diameter from a cylindrical job. •Taper turning can be done by the following ways;

• By a form tool.• By setting over the tailstock.• By swiveling the compound rest.• By taper turning attachment.• By compound feed.

Taper turningTaper turning

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Taper turning by a form tool Taper turning by a form tool uses a tool which is a broad nose tool having straight cutting edge.

The tool is set on the work piece at half taper angle, and is fed straight into the work to generate a tapered angle.

This method is limited to turn limited length taper only.

This is due to the reason that the metal is removed by entire cutting edge, and any increase in length of the taper will necessitate the use of a wider cutting edge.

This will require excessive cutting pressure, which may distort the work due to vibration and spoil the work due to vibration and spoil the work surface.

Work piece

Toolfeed

Taper turning methodsTaper turning methods

116Taper turning attachment

Taper turning methodsTaper turning methods

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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.

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Thread cutting operation

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Change gears of correct sizes are then fitted between the spindle and the leadscrew.

When the Change gears are not fitted and when the Change gears are fitted (in this case a compound drive is used)

Thread cutting operation

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Grinding Attachment

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Milling Attachment

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Turret Lathe

Figure 23.9 Schematic illustration of the components of a turret lathe. Note the two turrets: square and hexagonal (main).

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CAPSTAN AND TURRET LATHE

The standard engine lathe is versatile, but it is not a high production machine. When production requirements are high, more automated turning machines must be used. The turret lathe represents the first step from the engine lathe toward high production turning machines. The turret lathe is similar to the engine lathe except that tool-holding turrets replace the tailstock and the tool post-compound assembly. The ‘skill of the worker’ is built into these machines, making it possible for inexperienced operators to reproduce identical parts. In contrast, engine lathe requires a skilled operator and requires more time to produce parts that are dimensionally the same. The principal characteristic of turret lathes is that the tools for consecutive operations are set up for use in the proper sequence. Although skill is required to set and adjust the tools properly, once they are correct, less skill is required to operate the turret lathe.

Turret Lathe

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• The turret 1 is mounted on the spindle 5, which rests on bearing on the turret saddle.

• The index plate 2, the bevel gear 3 and the indexing ratchet 4 are keyed to the spindle 5.

TurretTurret indexing mechanism indexing mechanism

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• The plunger 14 fitted within the housing and mounted on the saddle locks the index plate by spring pressure 15 and prevents any rotary movement of the turret as the tool feeds into the work.

• A pin 13 fitted on the plunger 14 projects out of the housing.• An actuating cam 10 and indexing pawl 7 are attached to the lathe bed 9 at

the desired position.


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• Both the cam and the pawl are spring loaded. • As the turret reaches the backward position , the actuating cam 10 lifts the

plunger 14 out of the groove in the index plate due to the riding of the pin 13 on the beveled surface of the cam 10 and thus unlocks the index plate 2.

• The spring loaded pawl 7 which by this time engages with a groove on the ratchet plate 4 causes the turret to rotate as the turret head moves backward.


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• When the index plate or the turret rotates through one sixth of revolution, the pin 13 and plunger 14 drops out of cam 10 and the plunger locks the index plate at the next groove.

• The turret is thus index by one sixth of revolution and again locked into the new position automatically.

• The turret holding the next tool is now fed forward and the pawl is released from the ratchet plate by the spring pressure.


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• The ratio of the teeth between the pinion and gear are so chosen that when the tool mounted on the face of the turret is indexed to bring it to the cutting position, the particular stop rod for controlling the longitudinal travel of the tool is aligned with stop 12.


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• The setting of the stop rods 8 for limiting the feed of each operation may be adjusted by unscrewing the lock nuts and rotating the stop rods on the plate.

• Thus six stop rods may be adjusted for controlling the longitudinal travel of the tools mounted on the six faces of the turret.


lathe ppt

Documents

lathe centres

lathe saddle

small lathe

lathe ways

specifications of lathe

definition lathe

larger lathe

lathe bed heavy