Accessories with Their Functions Used For Lathe Machine
The lathe accessories are used for holding and supporting the work or for holding the cutting the various lathe accessories are discussed as follows
A general purpose machine tool is basically comprised of power drive and kinematic system for the essential formative and auxiliary tool – work motions and a rigid body or structure to accommodate all of the above. But several additional elements or devices called accessories are also essentially required for that machines’ general functioning, mainly for properly holding and supporting the workpiece and the cutting tool depending upon the type and size of the tool – work and the machining requirements.
a) There are two types of centres i.e., live centre and dead centre.
b) A centre which fits into the headstock spindle and revolves with the work is called live centre.
c) The centre which is used in a tailstock spindle and does not revolve is called dead centre.
a) It is an important device used for holding and rotating the workpiece in lathes.
b) The work pieces which are too short to be held between centres are clamped in a chuck.
c) It is attached to the lathe spindle by means of two bolts with the back plate screwed on to the spindle nose.
d) There are many types of the chuck, but the following two are commonly used.
i) Three jaw universal chuck.
The three jaw universal chuck, as shown in Fig. is also called self centering chuck or scroll chuck. Thus chuck is used for holding round and hexagonal work.
ii) Four jaw independent chuck.
1. The four jaw independent chuck, as shown in Fig. has four reversible jaws, each of which may be independently adjusted to accommodate the work it supports.
2. This type of chuck can hold square, round and irregular shape of work in either a concentric or eccentric position.
The other types of the chucks are
iii) combination chucks, iv) magnetic chuck, v) collect chuck, vi) drill chuck, and vii) air or hydraulic chuck
3. Lathe dog or carrier
a) The work placed on a mandrel or held between centres is rotated positively by clamping the dog or carrier to the end of the work.
b) This is engaged with a pin attached to the drive plate or face plate.
c) The lathe dog or carrier may be of straight type or bent type as shown in Fig.
4. Drive plate
a) The drive plate, as shown in Fig. is a circular plate which is bored out and threaded so that it can be attached to the spindle nose.
b) 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
5) Face plate.
a) The face plate, as shown in Fig. is similar to drive plate except that it is larger in diameter.
b) It contains more open slots or T-slots so that bolts may be used to clamp the workpiece to the face of the plate.
c) The face plate is used for holding work pieces which can not be conveniently held in a chuck.
6. Angle plate.
a) An angle plate is simply a cast iron plate with to faces planed at right angles to each other and having slots in various positions for the clamping bolts. b) It. is always used with the face plate for holding such parts which can not be clamped against the vertical surface of the face plate.
a) The lathe mandrel is a cylindrical bar with centre hole at each end. It is used to hold hollow work pieces to machine their external surface.
b) The work revolves with the mandrel which is mounted between the centres of the lathe. The various types of mandrels used for different classes of work are shown in Fig.
8. Steady, follower and other rests
Long workpieces often need to be supported in the middle, as cutting tools can push (bend) the work piece away from where the centers can support them, because cutting metal produces tremendous forces that tend to vibrate or even bend the workpiece. This extra support can be provided by a steady rest (also called a steady, a fixed steady, a center rest, or sometimes, confusingly, a center). It stands stationary from a rigid mounting on the bed, and it supports the workpiece at the rest’s center, typically with three contact points 120° apart.
A follower rest (also called a follower or a travelling steady) is similar, but it is mounted to the carriage rather than the bed, which means that as the tool bit moves, the follower rest “follows along” (because they are both rigidly connected to the same moving carriage)