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List and explain lathe accessories and attachments

We were discussing the types of lathe machines and their use, Different parts of the lathe machine and their functions and complete specifications of the lathe in our previous post.  


We will see the Accessories of a lathe machine i.e. devices that are used for holding and supporting the work and the tool on the lathe with the help of this post.  


So let's start now 


Chucks


Chucks are basically used for holding the workpiece on a lathe machine during the machining operation. Let us see the commonly used chucks as mentioned below   


  1. Three-jaw universal chuck 

  2. Four-jaw independent chuck 

  3. Combination chuck 

  4. Magnetic chuck 

  5. Collet chuck 

  6. Air or hydraulic operated chuck 

  7. Drill chuck


Three-jaw universal chuck 

In a three-jaw universal chuck or self centering chuck, as displayed in the following figure, all three jaws move together in equal amounts to clamp the work. Therefore the job is automatically centered. 


Figure 1 : Three-jaw universal chuck


The movement is achieved by rotating the chuck key in any one of the three pinions which meshes with the teeth cut on the underside of the scroll disc. The scroll disc having a spiral groove cut on the top face meshes with the teeth of jaws. The chuck is used for holding cylindrical or hexagonal shaped workpieces. 


Four-jaw independent chuck 

In a four-jaw independent chuck, as displayed in the figure, each jaw is moved independently by rotating the screw which meshes with the teeth cut on the underside of the jaw. These chucks are used for holding square, octagonal or large irregular components. 



Figure 2 : Four-jaw independent chuck 



Combination chuck 

A combination chuck carries the combination of both the above principles.

It is provided with four jaws which can be operated either by the scroll disc or individually by

separate screws.


Magnetic chuck 

These chucks are used to hold steel workpieces that are too thin to be held in an ordinary chuck. The face of the chuck is magnetized by permanent magnets contained within

the chuck. 


Collet chuck 

This chuck provides a quick means of holding the bar stock. Draw-in type collets are in common use. Their front portion is splitted which provides a spring action and hence the grip.


Air or hydraulic operated chuck 

Air or hydraulic pressure is used to press the jaws against the job in this chuck. The pressure is provided by a cylinder and piston mechanism mounted at the back of the headstock and controlled by a valve by an operator.


Drill chuck 

A drill chuck is used for holding straight shank drill, reamer or tap for drilling, reaming or tapping operations. This may be held either in the headstock or tailstock. This has self-centering jaws and is operated by a key. 


Face plate

A face plate is a large circular disc having a threaded hole at the center so that it can be screwed to the nose of the lathe spindle. It contains open slots or T-slots in its face. The workpiece is mounted on it with the help of bolts, T-nuts and other means of clamping. It is used for holding workpieces that cannot be conveniently held by chucks.


Angle plate

An angle plate is used for holding a workpiece in conjunction with a face plate. If mounting of the workpiece directly on the face plate is not possible, the angle plate is used for that purpose.


Lathe centers 

Lathe centers are hardened steel devices used for holding and locating the work to be turned. The center that is fitted in the headstock spindle is called the live center. The center that is used in the tailstock is called dead center. The various forms of lathe centers are shown in the following figure. 


 

Figure 3 : Lathe centers 


Ordinary center:

This is used for most general works 


Ball center:

This has a ball shape at the end to minimize the wear and strain. This is particularly suitable for taper turning. 


Tipped center:

In the tipped center, a hard alloy tip is brazed into a steel shank. The hard tip is wear resistant. 


Half center:

The half center is similar to an ordinary center except that a little less than half of the center has been ground away. This feature facilitates the facing of the bar ends without removal of the center. 


Revolving center:

The ball and roller bearings are fitted into the housing to reduce friction and to

take up end thrust. This is used in the tailstock for supporting heavy work revolving at a high speed. 


Pipe center: This is used for supporting pipes, shells and hollow end jobs. 


Lathe cutting tools   


Cutting tools used for machining are classified into two groups 


  1. Single point cutting tool 

  2. Multipoint cutting tool 


Single point cutting tools have only one cutting edge, while multipoint cutting tools have several cutting edges (drill, milling cutter). Single point cutting tools are used on lathes.


Single point lathes tools classification 


Single point lathes tools are classified in many ways. The main classification is as mentioned below. 


According to the direction of feed: 


The tools may be right-hand and left-hand threaded tools. In a right-hand tool, the cutting edge is on the left-hand side of the operator, the right-hand tool cuts from right to left, i.e. tool is fed from the tailstock to the headstock. In a left-hand tool, the cutting edge is on the right-side of the operator. The left-hand tool cuts from left to right as shown in the following figure.  



Figure 4 : Right hand tools and Left hand tools 


According to method of manufacturing the tool: 


These tools may be classified as mentioned below 

  1. Solid tool 

  2. Brazed tool 

  3. Inserted or bit tool


A solid tool is made of either high speed steel or carbide bar and the cutting edge is formed

by grinding one end of the bar. In a braze tool, the carbide tip is brazed to a shank of low grade material. In an inserted bit tool, the carbide or ceramic bit or a square or rectangular shape is held mechanically in a tool holder. 


According to the method of using the tool: 

Single point tools are classified as turning, facing, cutting off, boring, grooving, etc.  


Tool nomenclature 


The cutting tool nomenclature comprises the various parts of a tool and various tool angles. The complete nomenclature of a single point cutting tool is displayed in the figure.  


  1. Face : It is the surface over which the chip flows. 

  2. Flank : It is the surface below the cutting edge. 

  3. Nose : The nose is the junction of the side and end cutting edge.  

  4. Side cutting edge : It is formed by the intersection of the flank and the side flank. 

  5. It does the main work in cutting.

  6. End or Auxiliary cutting edge : It is the intersection of face end flank.

  7. Tool angles : In a single point tool, there are various angles, each of them has a definite purpose.


Figure 5 : Single point cutting tool nomenclature 


Back rake angle: 

It measures the downward slope of the top surface of the tool from the nose to the rear along the longitudinal axis. Its purpose is to guide the direction of chip flow. The size of the angle depends upon the material to be machined. 


A back rake angle may be positive, neutral or negative. The angle is positive if the face slopes downwards from the tip towards the shank. It is used to cut low tensile strength and nonferrous materials. The angle is negative if the face slopes upwards. It is used to cut high tensile strength materials for heavy feed and interrupted cuts. 


Side rake angle:  

It measures the slope of the top surface of the tool to the side in a direction perpendicular to the longitudinal axis. It also guides the direction of the chip away from the job.


Side relief angle: 

It is the angle made by the flank of the tool and a plane perpendicular to the base just under the side cutting edge. This angle permits the tool to be fed sideways into the job, so that it can cut without rubbing. 


End relief angle: 

It is the secondary relief angle between a plane perpendicular to the base and

the end flank.


Side cutting edge angle: 

It is the angle between the side cutting edge and the longitudinal axis of the tool. 


Nose radius: 

It is the curve formed by joining the side cutting and end cutting edges. The angle so formed between cutting edges is called nose angle and the radius of the curve is called nose radius. 


We will now study the various Lathe operations with the help of the next post. 


Reference

Engineering Practices by Mr. S. SUYAMBAZHAHAN 

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