LATHE MACHINE
Working Principle: The lathe is a machine tool which holds the workpiece between two rigid and strong supports called centers or in a chuck or face plate which revolves. The cutting tool is rigidly held and supported in a tool post which is fed against the revolving work. The normal cutting operations are performed with the cutting tool fed either parallel or at right angles to the axis of the work.
The cutting tool may also be fed at an angle relative to the axis of work for machining tapers and angles.
Construction: The main parts of the lathe are the bed, headstock, quick changing gear box, carriage and tailstock.
1. Bed: The bed is a heavy, rugged casting in which are mounted the working parts of the lathe. It carries the headstock and tail stock for supporting the workpiece and provides a base for the movement of carriage assembly which carries the tool.
2. Legs: The legs carry the entire load of machine and are firmly secured to floor by foundation bolts.
3. Headstock: The headstock is clamped on the left hand side of the bed and it serves as housing for the driving pulleys, back gears, headstock spindle, live centre and the feed reverse gear. The headstock spindle is a hollow cylindrical shaft that provides a drive from the motor to work holding devices.
4. Gear Box: The quick-change gear-box is placed below the headstock and contains a number of different sized gears.
5. Carriage: The carriage is located between the headstock and tailstock and serves the purpose of supporting, guiding and feeding the tool against the job during operation. The main parts of carriage are:
a). The saddle is an H-shaped casting mounted on the top of lathe ways. It provides support to cross-slide, compound rest and tool post.
b). The cross slide is mounted on the top of saddle, and it provides a mounted or automatic cross movement for the cutting tool.
c). The compound rest is fitted on the top of cross slide and is used to support the tool post and the cutting tool.
d). The tool post is mounted on the compound rest, and it rigidly clamps the cutting tool or tool holder at the proper height relative to the work centre line.
e). The apron is fastened to the saddle and it houses the gears, clutches and levers required to move the carriage or cross slide. The engagement of split nut lever and the automatic feed lever at the same time is prevented she carriage along the lathe bed.
6. Tailstock: The tailstock is a movable casting located opposite the headstock on the ways of the bed. The tailstock can slide along the bed to accommodate different lengths of workpiece between the centers. A tailstock clamp is provided to lock the tailstock at any desired position. The tailstock spindle has an internal taper to hold the dead centre and the tapered shank tools such as reamers and drills.
LATHE OPERATIONS
The engine lathe is an accurate and versatile machine on which many operations can be performed. These operations are:
Step Turning: Step turning produces various steps of different diameters.
Facing: The facing is a machining operation by which the end surface of the work piece is made flat by removing metal from it.
Parting: The parting or cutting off is the operation of cutting away a desired length of the workpiece, i.e., dividing the workpiece in two or more parts.
Drilling: Drilling is the operation of producing a cylindrical hole in the workpiece.
Reaming: The holes that are produced by drilling are rarely straight and cylindrical in form. The reaming operation finishes and sizes the hole already drilled into the workpiece.
Boring: The boring operation is the process of enlarging a hole already produced by drilling.
Knurling: The knurling is a process of embossing (impressing) a diamond-shaped or straight-line pattern into the surface of workpiece. Knurling is essentially a roughening of the surface and is done to provide a better gripping surface.
Grooving: Grooving is the act of making grooves of reduced diameter in the workpiece.
Threading: Threading is the act of cutting of the required form of threads on the internal or external cylindrical surfaces.
Forming: The forming is an operation that produces a convex, concave or any irregular profile on the workpiece.
Filing and Polishing: The filing is the finishing operation that removes burrs, sharp corners and feed marks from the workpiece. After filing, the surface quality is the workpiece is improved by the polishing operation with the help of emery cloth of fine grades.
Taper Turning: The taper turning is an operation of producing a conical surface by gradual reduction in the diameter of a cylindrical workpiece.
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