Unite-II LATHE

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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
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Introduction

• A lathe is a machine tool which spins a block of
  material to perform various operations

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Introduction

• 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.

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Turning Parameters

• 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

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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.

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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).

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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),

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Machine Classification

• Size designation
• Swing - maximum diameter that can be rotated on
  the lathe
• 2xs distance from spindle center line to ways
• Maximum distance between centers

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Size of Lathe
Swing
Workpiece Length
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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)

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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 12x24 to 24x48 - can be larger
• Bench Lathe
• A bench top model usually of low power used to
  make precision machine small work pieces

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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

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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

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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

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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

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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

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Computer Numerically Controlled Lathes

• Fig A computer numerical control lathe. Note
  the two turrets on this machine.

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Component Description
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Lathe Basics
Spindle Nose
Tailstock Spindle Clamp
Tool Post
Compound Rest
HEADSTOCK
TAILSTOCK
Saddle
Feed Change Lever
Feed Reverse Lever
Lead Screw
BED WAYS
APRON
Bed
Gear Box
Half Nut Lever
Friction-clutch Control
Carriage Hand Wheel
Motor Drive
Cross Slide
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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
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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.
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Carriage Feed
Power Feed for Turning Facing Used for greater
control and accuracy. Speed controlled by the
Quick Change Gear Box
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Carriage and Apron
The controls on the carriage and apron control
all the tool and carriage movement.
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Lathe Carriage and Apron
Tool Post
Compound Rest
Carriage Lock Screw
Cross Feed Knob
Cross Slide
Apron Hand Wheel
Apron Feed Change Lever
Half Nut Lever
Power Feed Clutch
Compound Rest Knob
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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
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Apron Hand Wheel
Used to move tool along the work - for Turning
(Longitudinal Feed)
Apron Hand Wheel
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Cross Feed Knob
Used to move cutting tool across the end of the
stock - Facing (Cross Feed)
Cross Feed Knob
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Power Feed Clutch
Engages the power feed for turning or facing
operations
Power Feed Clutch
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Apron Feed Change Lever
Switches power feed between turning and facing
directions
Apron Feed Change Lever
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Chuck
Three Jaw Chuck - For holding cylindrical stock
centered. - For facing/center drilling the end of
your aluminum stock
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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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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.
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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
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Collet Chuck
Collet chuck is used to hold small workpieces

• Thin jobs can be held by means of magnetic
  chucks.

Magnetic Chuck
Thin jobs can be held by means of magnetic
chucks.
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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 whenadjusted 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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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
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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

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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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Spring Collet Chucks
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Spring Collet Chucks
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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
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Cutting Speed
D Diameter (mm) N Revolutions per Minute (rpm)

• The Peripheral Speed of Workpiece past the
  Cutting Tool
• Cutting Speed

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Feed

• f the distance the tool advances for every
  rotation of workpiece (mm/rev)

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Depth of Cut

• perpendicular distance between machined surface
  and uncut surface of the Workpiece
• d (D1 D2)/2 (mm)

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Operating Conditions
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Cutting Tool
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Turning Between Centers
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Some Typical Lathe Jobs

• Turning/Drilling/Grooving/
• Threading/Knurling/Facing...

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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
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Lathe Operations

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Turning
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Turning ..

• Cylindrical job

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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

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Facing

• Flat Surface/Reduce length

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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

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Facing ..
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Eccentric Turning
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Knurling

• Produce rough textured surface
• For Decorative and/or Functional Purpose
• Knurling Tool
• A Forming Process
• MRR0

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Knurling
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Grooving

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

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Grooving ..
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Parting

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

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Parting ..
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Chamfering
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Chamfering

• Beveling sharp machined edges
• Similar to form turning
• Chamfering tool 45
• To
• Avoid Sharp Edges
• Make Assembly Easier
• Improve Aesthetics

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Taper Turning

• Taper

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Taper Turning..
Conicity

• Methods
• Form Tool
• Swiveling Compound Rest
• Taper Turning Attachment
• Simultaneous Longitudinal and Cross Feeds

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Taper Turning ..By Form Tool
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Taper Turning ,,By Compound Rest
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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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Types of Screw threads
Fig Various types of screw threads
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Drilling

• Drill cutting tool held in TS feed from TS

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Drilling
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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 drills performance

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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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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

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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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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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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

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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.

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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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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

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Standard bent-tail lathe dog

• Most commonly used for round workpieces
• Available with square-head setscrews of headless
  setscrews

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Standard bent-tail lathe dog

• Bent tail engages in slot on drive plate

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Straight-tail lathe dog

• Driven by stud in driveplate
• Used in precision turning

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Safety clamp lathe dog

• Used to hold variety of work
• Wide range of adjustment

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Heavy Duty Lathe Dog

• Wider range than others
• Used on all shapes

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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

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Super Quick-Change Toolpost
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Simple formula
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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.
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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 ?DN/1000 M/min

Required spindle speed as N 191 rpm
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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) / 2?80 or ? 10.620
• The compound rest should be swiveled at 10.62o

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