LATHE ACCESSORIES:-
The device which helps to improve the efficiency of performing a usual lathe operation is known as a lathe accessory. And here we are going to study 10 Lathe accessories in detail, so The various lathe accessories include the followings :-
- 1. Centres.
- 2. Lathe dog or carrier.
- 3. Chucks,
- 4. Collects
- 5. Face plates,
- 6. Driving plate.
- 8. Mandrels.
- 7. Angle plate
- 9. Rests
- 10. Milling attachment,
1.Centres:-
Work piece is held in lathe between two centres ,live centre and dead centre.These two centres take up the thrust due to metal cutting and the entire load of the workpiece on small bearing surface.
So these are made of very hard materials to resist deflection and wear. The Included angle of the centre is usually 60° for general purpose work and 75° for heavy work. The shank of all the centres are machined to the morse (0 - 6) or metric (4 & 6) standard tapers. Table 2.1 shows the types of centres and their applications.
2. Lathe Carrier or Dog:-
It is a device which carries the workpiece alongwith the rotating driving plate, when the work is held between centres.
A carrier or driving dog is attached at its eyes end to the end of the workpiece by one or two clamping screws. Its leg end engages with the driving pin of driving plate or with slot of the later when the leg is a bent type. Sometimes, the carrier is having two slots, the outer side of its body will engage with two driving pins projecting from the driving plate.
3.Chuck :-
It is an important device used for holding and rotating the workpiece in a lathe. The workpiece of short length and large diameter or of irregular shape which cannot be held between dead centres is held quickly and rigidly in a chuck.
A chuck is attached to the lathe spindle by means of bolts with back plate screwed on to the spindle nose. There are many types of the buck, but the followings are commonly used:
(i)Four Jaw Independent Chuck : -
It has four reversible jaws, each of which may be independently adjusted to accomodate the work.Since movement of all the jaws is independent.so it can be used for prismatic parts (i.e. square, round or irregular shape) and the work can be ne in either a concentric or eccentric position, but centring is needed.this figure show a four jaw independent chuck.
(ii) Three Jaw Universal Chuck :-
This chuck is also called the self centering chuck or scroll chuck. Here all the jaws may be made to slide simultaneously by an equal amount within the slots provided on the body by rotating any one of three pinions which meshes with teeth cut on the underside of scroll disc.
The scroll disc having a spiral groove cut on the top face meshes with the teeth on the jaws. w hen the disc is made to rotate by any one of the pinion, all the three jaws move backward or forward by equal amount. It is used for holding round and hexagonal work because centering is not needed.
(iii)Combination Chuck :-
it is used as self centering and an independent chuck to take advantages of both the types. The jaws may be operated individually by a separate screw o simultaneously by the scroll disc.
(iv) Magnetic Chuck:-
This chuck is used for holding a very thin workpiece made of magnetic material which cannot be held in ordinary chuck. This chuck will not produce any scratches on the job.
4. Collets :
They are the most accurate of the chuck family. They are like three jaw chucks and are used for bar stock or other sections upto about 63 mm. e.g. round, square, hexagonal etc.
5. Face Plate :
Face plate is similar to drive plate except that it is large in diameter. It consists of a circular disc bored out and threaded to fit the nose of the plate spindle. It has radial plain and T-slots so that bolt can be used to clamp the work of complicated shape and size which cannot be held in chuck.
6. Drive Plate (Catch Plate) :-
It is a circular plate which is bored out and threaded so that it can be attached to the spindle nose. It also carries a hole for the pin which is used only when the work is held in a lathe dog having straight tail. When bent-tail dog is used, this pin is taken out and the bent portion of the tail is inserted into the hole.
7. Angle Plate :-
it is simply a cast iron plate with two faces planed at right angle to each other and having slots in various positions for clamping bolts. It is always used with the face plate for holding such parts which cannot be clamped against the vertical surface of the face plate.
8. Mandrel :-
It is used to locate and hold a work-piece with a central hole such as gear blanks, pulleys etc. It is a solid hardened bar with centres and flats on cach end. A mandrel is held between the centres and rotated with a lathe dog clamped on its flat. The mandrel is usually tapered and taper is about 0.005 mm per em length. The work can be forced on it with press then removed after working.
9. Rest :-
It is a mechanical device which supports a long slender workpiece, when it is turned between centres or by a chuck, at some intermediate point to prevent bending of workpiece due to its own weight and vibration set up due to cutting forces that act on it.
should always be used when the length of workpiece is 10 - 12 times the diameter.
- (i) Greatest accuracy in machining
- (ii) Heavier depth of cut on the workpiece.
It is of two types :-
- (a) Steady or centre rest,
- (b) Travelling follower rest.
(a) Steady Rest :
It consists of a cast iron base which may be made to slide on the lathe bed ways and clamped at any desired position on guide ways of lathe bed by nuts where a support it necessary. The work is held between three jaws which can be adjusted radially by rotating individual screws to accommodate workpieces of different diameters.
(b) Travelling or Follower Rest :
It used to support the work which is close to the cutting tool. It is bolted to the cross slide on the saddle and travels with the tool as it feeds along the work.
10. Tool Post Grinder :
A typical form of this attachment is shown in fig. It consists of a bracket which is mounted on the cross-slide, a grinding wheel and a separate motor as shown in fig.Thus the grinding wheel is driven separately by this motor. The workpiece is held in. a chuck or between centres and the rotating grinding wheel is fed against the job. In fig. the attachment shown is for external grinding. Some tool post grinders carry provision such that the same attachment with a little change can be used for internal as well as external grinding.
11. Milling Attachment :-
Milling Attachment of a vertical pillar upon which an individual motor and a device to mount the cutter are attached. Base of the pillar is rigidly fastened to the saddle and the unit holding the motor and the cutter can be moved vertically up and down with the help of screw and the handwheel provided at the top of the pillar.
12. Tapering By Taper Turning Attachment :-
In this method of taper turning, the tool is guided in a straight path at an angle to the axis of rotation of the workpiece. Different lathes are provided with different designs of taper turning attachment, but all of them work on the same principle. During the process, the work revolves between centres and the tool is guided in a straight path set at an angle to the lathe axis by means of taper turning attachment. The attachment consists of bracket or frame, guide bar and guide block.
