Monday, August 5, 2013

LATHE machine is mother of all machines

the lathe machine
LATHE



      Definition

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

     Common types of lathes: 

Engine 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.
Automatic Lathe:

The lathe in which the work piece is automatically fed and removed without use of an operator.  Cutting operations are automatically controlled by a sequencer of some form.

Turret Lathe:

The lathes which have multiple tools mounted on turrent either attached to the tailstock or the cross-slide, which allows for quick changes in tooling and cutting operations.

Computer Controlled Lathe:

Highly automated lathes, where cutting, loading, tool changing, and part unloading are automatically controlled by computer coding.

 The figure (1) shows Photographic view of Engine Lathe

            


Fig (1) Engine Lathe

Centre lathe – constructional features
·         Head stock
·         Tail stock
·         Bed
·         Carriage
·         Feed rod
·         Lead screw
·         Feed change gear box

Lathe specifications
·         Distance between centers
·         Swing over the bed
·         Swing over the cross slide
·         Horse power of the motor
·         Number of speeds
·         Number of feeds                                                  
Lathes and Lathe Operations


         Lathes are the oldest machine tools

         Lathe Components


·         Bed: supports all major components
·          
·         Carriage: slides along the ways and consists of the cross-slide, tool post, apron

·         Headstock – Holds the jaws for the work piece, supplies power to the jaws and has various drive
Speeds
         Tailstock – supports the other end of the work piece

         Feed Rod and Lead Screw – Feed rod is powered by a set of gears from the headstock

LATHE BED


·         The bed is the base of the lathe and supports all the major components of lathe.

·          Lathe bed material made of grey cast iron , to resist deflection and absorb vibrations during cutting


Carriage Feed
·           Longitudinal Feed or “Turning” - The tool is fed along the work.
·         Cross Feed or “Facing” – The tool is fed across the work.


Tail Stock:

It’s like a stationary drill press

It is centered with your work piece

For drilling use a drill chuck that fits your bits

Jam the drill chuck into the tail stock

To remove the chuck turn the tail stock back to zero and the chuck should pop out

Cutting Tools


There are basically two types of cutting tools:

·         Single point (e.g. turning tools). ( fig .2 )

·         Multiple point (e.g. milling tools).


Fig (2) shows single point cutting tool

Fig ( 2)
Various lathe operations

         Turning – produces straight, conical, curved, or grooved work pieces

         Facing – produces a flat surface at the end of the part

         Boring – to enlarge a hole

         Drilling - to produce a hole

         Cutting off – to cut off a work piece

         Threading – to produce threads

         Knurling – produces a regularly shaped roughness

Fig (3) shows  different types of lathe operations




Fig (3) Types of Lathe operations














Work holding Devices for Lathes:

 Many different devices, such as chucks, collets, faceplates, drive plates, mandrels, and lathe centers are used to hold and drive the work while it is being machined on a lathe.


Work pieces can be held by various methods

·         Work piece mounted between centers

·         Work piece mounted within a single chuck

·         Work piece mounted within a collet

·         Work piece mounted on a faceplate



Three Jaw chuck: It usually has three jaws, the jaws are moved simultaneously within the chuck (fig.4).

Four Jaw chuck: This is independent chuck generally has four jaws , which are adjusted individually on the chuck face by means of adjusting screws(fig.5).

Magnetic chuck: Thin jobs can be held by means of magnetic chucks.

Face plates: The face plate is used for irregularly shaped work pieces that cannot be successfully held by chucks or mounted between centers (fig.6).

Mandrels: A work piece which cannot be held between centers because its axis has been drilled or bored and which is not suitable for holding in a chuck or against a faceplate is usually machined on a mandrel.

Collet chuck :  Collet chuck is used to hold small work pieces.









3 JAW CHUCK                                 4 JAW CHUCK          
                                                                                                                         

Fig.(4)                                                 Fig.(5)



  FACE PLATE


                                                                        Fig,.6 Face plate
Formulas:

Cutting speed (V) = ΠDN/1000 M/min

Depth of cut (D) = (D1-D2)/2 mm

Where D1=original diameter and D2 = final diameter of the work piece    

Metal Removal Rate (MRR) = Π x D x d x f       mm3

In terms of cutting speed (V in mm/min), MRR=1000 x V x d x f

   Where D represents original diameter of the work piece in mm
   Where N represents revolution per minute (rpm)

  Where d represents depth of cut in mm

  Where f represents feed in mm/rev

   Taper Turning
    Tan α = (D1- D2)/2L   where α = angle of taper

    D1= major diameter in mm
    D2= minor diameter in mm
    L= Length of taper in mm
   The conicity K of the taper is defined as K= (D1- D2)/L

















 Lathe 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.

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
Required spindle speed as: N = 191 rpm

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 a = (80-50) / 2´80       or       a = 10.620
                       
The compound rest should be swiveled at 10.62°



           
Reference

         work shop Technolgy by Hajra choudry
          Advances in Manufacturing Technology C.J Thomas

Website
          www. engbasics.com
          www. efunda.com.


  
  

(Part-A)

  1. What do you mean by lathe?
2.   What are all the various operations can be performed on a lathe?
  1. What are all the principle parts of the lathe?
  2. Difference between three jaw chuck and four jaw chuck
  3. State the various parts mounted on the carriage?
  4. write  four types of tool post
  5. What is an apron?
  6. State any two specification of lathe?
  7. List any four types of lathe?
  8. What do you mean by semi-automatic lathe?
  9. State the various feed mechanisms used for obtaining automatic feed?
  10. List any four holding devices?
  11. What are the different operations performed on the lathe?
  12. State any two specifications of capstan lathe & turret lathe?
  13. Compare the advantage of capstan lathe & turret lathe?
  14. Define tooling?
  15. What are the three stage of a tool-layout?
  16. What are the different drives used in copying lathe?
  17. What are the components that can be turned on a copying lathe?
  18.  Define automatic lathes.
(Part –B)
1.      Explain the different components of a lathe with neat sketch.
2.      What are the different operations that can be performed on a lathe? also , mention the tools required for each operation
3.      What are the different machining operations that can be performed on a lathe? Explain any five in detail.
4.      Explain the different work holding devices used in a lathe?
5.      write short notes on
a.       universal scroll chuck              b. magnetic chuck
c.       collet chuck                             d. centers
6. Explain the following operations performed on lathe with suitable sketch.
   a. turning
b. facing
c. grooving
d. knurling
d. thread cutting
7. Explain the different methods of holding the work piece in a lathe with suitable sketches.

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