Plain Turning:

This method of machining operation in which the workpiece is reduced to the cylindrical section of required diameter is called turning. 

The workpiece is supported inbetween the two centers which permits the rotation of the workpiece . A single point cutting tool is fed perpendicular to the axis of the woekpiece to a known predetermined depth of cut, and is then moved parallel to the axis of the workpiece. This operation will cut the material which comes out from the workpiece.

Lathe Operations:

All most all the basic machining operations can be performed on a lathe. Some of the very important and generally performed lathe operations are:

1. Turning

2. Taper turning

3. Thread cutting

4. Boring

5. Facing 

6. Drilling

7. Reaming

8. Knurling

9. Milling

10. Grinding

Single Point Lathe Tool

In a single point cutting tool, there will be a point contact between the cutting tool and the workpiece. Obviously the cutting tool should be provided with the clearances on the top. Underside and the side face. The cutting portion of the tool is formed by a face, cutting edge, flank, nose and base. 

The face is the top of the tool and is the surface over which the chip glides over it and passes away from the workpiece. 

The cutting edge is the part of the tool that does the actual cutting of the metal. 

The flank is the tapered surface directed below the cutting edge. 

The nose is the tip of the tool bit formed by the side and the end edges. 

The base is the bottom surface of the tool.

The functions of the different cutting tool angles are as follows:

1. Relief or clearance angles are ground on both the end and side faces of a tool to prevent it from rubbing on the workpiece.

2. Slide relief is the angle ground directly below the cutting edge on the flank of the tool.

3. End relief is the angle grounded from the nose of the tool.

4. Relief angles are necessary to enable only the cutting edge to touch workpiece.

5. Rake angles are ground on a tool to provide a smooth flow of the chip over the tool bit so as to move it away from the workpiece.

6. Side rake angle is ground on the tool faces away from the cutting edge. Side rake influences the angle at which the chip leaves the workpiece. A lathe tool generally uses side and back rakes. A general purpose lathe tool has a 14 degree side rake.

7. Back rake is ground on the face of the tool. Back rake angle influences the angle at which the chip leaves the nose of the tool. Generally 8 to 10 degree back rake is provided. 

8. End and side cutting edge angles are ground on a tool so that it can be mounted in the correct position for various machining operations.

9. End cutting edge angle usually 20 to 30 degree allows the cutting tool to machine close to the workpiece during turning operations.

10. Side cutting edge angle, approximately 15 degree, allows the flank of the tool to approach the workpiece first, thus reducing the initial shock of the cut to the tip point. This angle spreads the material over a greater distance on the cutting edge, thereby thinning out the chip.

11. Nose radius is the rounded tip on the point of the tool. The nose radius has tow functions to prevent the sharp fragile tip from breaking during use, and to provide a smoother finish on the workpiece during machining operations. A nose radius of 0.8 mm works well with most of the operations.

functions of lathe

MAJOR FUNCTIONS:

• BED: The bed is the foundation of a lathe and supports all its parts. The top of the bed is formed by precision machined guideways. There will be two sets of guideways, viz... Outerways and Innerways. The headstock and the tailstock are mounted on the innerways which keep them perfectly aligned with each other. The outerways guide the longitudinal movement of the carriage assembly and align it with the centre line of the lathe.

• MAIN DRIVE: An electric motor mounted in the left leg of the lathe in conjunction with the transmission system like belt or gear drive from the motor to the spindle that form the main drive of the lathe.

• CONE PULLEY AND BACK GEAR: The cone pulley which drives the main spindle through belting is driven by the motor. Various spindle speed can be obtained by shifting the belt on the different steps of the cone pulley. Spindle speed can be further varied using a back gear arrangement.

• HEADSTOCK: The housing comprising of the feed gear box and the cone pulley is called headstock of the lathe. The main spindle projects out from the headstock. The headstock will be rigidly mounted on the lathe bed at its left end.

• TAILSTOCK: It is the movable part of the lathe that carries the dead centre in it. The main function of tailstock is to support the free end of the long workpiece. It also used to clamp the tools like twist drills and reamers for making holes, and taps and dies for cutting threads. Tailstock is mounted loosely on the lathe bedways and can be moved and locked in any desired position. 

• LEAD SCREW: It is a screw rod which runs longitudinally infront of the lathe bed. The rotation of the lead screw moves the carriage to and fro longitudinally during thread cutting operations.

• FEED ROD: The feed rod is a stationary rod mounted infront of the lathe bed and facilitates longitudinally movement of the carriage during turning, boring and facing operations.

• FEED GEAR BOX: The feed gear box is mounted on the left side of the lathe bed and below the headstock. It houses the necessary gears and other mechanisms that transmit various feed gear ratios from the headstock spindle to either the lead screw or the feed rod.

• CARRIAGE ASSEMBLY: The carriage assembly serves to support the tool and rides over the bedways longitudinally between the headstock and tailstock. It is composed of five main parts.

a) Saddle: is a H shaped casting slides over the outer set of the guideways and serves as the base for the cross slide.

b) Cross Slide: is mounted on the saddle and enables the movement of the cutting tool laterally across the lathe bed by means of cross-feed hand wheel. It also serves as the support for a compound rest.

c) Compound Rest: is mounted on the top of the cross slide and supports the tool post. It can be swiveled to any angle in the horizontal plane to facilitate the taper turning and threading operations. It is moved manually by the compound rest feed handle independent of the lathe cross feed.

d) Apron: is mounted at the front of the saddle beneath it and houses the carriage and the cross slide mechanisms. The apron hand wheels moves the carriage assembly manually by means of the rack and the pinion gears.

e) Tool Post: is mounted in the T slot of the compound rest. The tool post clamps the tool holder in the proper positions for machining operations.

lathe parts

. Major parts of a lathe:

1. Bed

2. Main Drive

3. Cone Pulley and Back Gear

4. Headstock

5. Tailstock

6. Lead Screw

7. Feed Rod

8. Carriage Assembly consist of:

a. Saddle

b. Cross-slide

c. Compound Rest

d. Apron

principle of working

   A lathe, basically a turning machine works on the principle that a cutting tool can remove material in the form of chips from the rotating workpieces to produce circular objects. This is accomplished in a lathe which holds the workpieces rigidly and rotates them at high speeds while a cutting tool is moved against it.

EX: A workpiece held rigidly by one of the working devices, know as chunk, and is rotated at very high speed. A V-shaped cutting tool held against the workpiece opposite to its direction of rotation when moved parallel to the axis of the workpiece produces circular surfaces. The material of the tool will be harder and stronger than the material of the workpiece.

 Lathe Specifications:

The size of the lathe is specified by the following:

1. Maximum diameter of the workpiece that can be revolved over the lathe bed. Instead of this sometimes, the height of the centers above the lathe bed is also specified. One of these specifications is given by the manufacturers; however both of them are loosely called as “Swing of the lathe”.

2. The maximum diameter and the width of the workpiece that can swing when the lathe has a gap bed.

3. The maximum length of the workpiece that can be mounted between the centers.

4. Overall length of the bed. It is the total length of the lathe itself.

LATHE

Introduction:

    Several metal cutting operations are carried out to produce a required shape and size. The metal cutting operations may be carried out either manually by using hand tools such as chisels, files, saw, etc, or using metal cutting machines. When machines perform the metal cutting operation by the cutting tool mounted on them, they are called “machine tools”. A machine tool may be defined as a power driven machine which accomplishes the cutting or matching operation on it. The fundamental machines tools that are used for most of the machining processes are lathe, drilling, tapping, planning, milling, and grinding machines.

LATHE:

  

A lathe is a machine tool employed generally to produce circular objects. It is said to be the mother of all machine tools, since it is so versatile, that all the machining operations which are performed on other machine tools like, drilling, grinding, shaping, milling, etc, can be performed on it.

Various types of lathes are being used in practice to perform variety of machining operations. Depending on their characteristics functions, lathes are classified as:

1. Engine Lathe

2. Speed Lathe

3. Turret Lathe

4. Capstun Lathe

5. Automatic Lathe

6. Computer Numerically Controlled (CNC) Lathe

                                             3D-view of lathe