StopLearnStopLearnA machine tool is a machine that cuts metals and performs some other operations by manipulation of its parts. This chapter introduces you to the five basic machines normally regarded as machine tools.
Content:
Types of Metal work
Machines and their Functions
iii. Milling machine
Modern machinery production technology has made it possible to manufacture other production machine tools for special purposes by utilizing the technology of these basic ones. In this chapter, we shall briefly present the functions and uses of these machine tools.
Lathes
There are two types of metal lathes – the plain lathe and the screw cutting lathe. The purpose of a lathe is to remove metal by use of a rigidly controlled hard steel-cutting tool. The revolving is the held firmly in a chuck or between centres while the tool cuts. Lathes are equipped with various devices as presented below:
Taper Turning
Taper turning is the production of a piece of round work in which one end is bigger than the other. It is always a conical shape. There are few methods by which the shape could be produced on the lathe. Tapering with a form tool is the simplest. It involves the use of shaped tool or cutter fed into the work piece to produce the taper required. Such tapers are termed short tapers and can be used for either internal or external turning.
Surfacing
Surfacing is achieved when the cutting tool moves perpendicular to the axis of rotation of the job being machined and therefore produces a flat surface. A good face is got when a suitable surfacing tool is used. While surfacing to the center point of a work, it is important to set the tool tip to the exact centre height. On the other hand, if the tool moves parallel to the axis of rotation of the workpiece, a cylindrical surface is produced. This is called a plane face.
Turning of a series of plain diameters on a work piece can simply be carried out on the centre lathe. This is better achieved with the use of carriage movement, because the straightness of the bed ways ensures the parallelism of the workpiece, and can be power-operated and produced at one setting. The further maintains concentricity between the different diameters. If the workpiece is removed for any reason while still turning, accuracy is lost, and this should be avoided. This process is ideal in producing what is termed stepping turning.
Sawing
The power sawing machine is used to cut the soft material with coarse tooth back-saw blades. The coarse tooth ensures that the metal chips do not clog the teeth. There are many brands of the hack sawing machine but a good one is the type incorporated with relief of pressure on return stroke by oil pump or by adjustable oil dash pot in conjunction with the angular setting of the slide. The work piece should be gripped rigidly, and the frame lowered carefully to start the cut.
Abrasives
In metal working, two types of abrasive are used. These are aluminium oxide and silicon carbide. Silicon carbide is suitable for the grinding of materials of low tensile strength such as iron, brass, bronze, copper, aluminium and cemented carbide.
Its abrasive forms are obtainable in powder form, grinding paste, lapping compound wheels and variously shaped stones and on cloth or paper in grades O, FF, 1, 1½, 2, 2 2/2 – 3 to 4 which is the coarsest.
Drill Press
Small diameter holes can be drilled with the use offhand drills, as the holes to be drilled becomes larger, the handle of the drill can be replaced with breast plates at right angles.
(Most work is gripped in a vice, fastened to work table with boils. The bottom of the vice must be parallel, and square to the jaws.
It is dangerous to drill a piece of work on the drill press without holding the job firmly and securely. In order to avoid accidents, it is necessary to clamp down the work to the body of the drill, thus becoming breast drill as much pressure is needed, say about 25mm or over, hand powered drilling machine can be used, or a drilling pillar and a ratchet brace. For thicker metal boring, the use of power-driven sensitive drilling machine can be used. The work table is a special vice or jig as the case may be. Work held by hand on a drill press often results in injuries, and should be avoided. These are twist drill, combination drill, reamer (sunblind drill), countersink, counter bore cutter, spot face cutter, trepanning tool, tap, etc.
Cutting Fluids
These are sometimes called coolants or cutting lubricants. They are important on machine tools. They are used to:
Coolant may be divided into three main classes:
Soluble oils: These are mineral oils treated to form an emulsion when added to water. They can be used neat, or diluted with water to increase their cooling powder.
They usually leave on the machine a protective cooling or film that is rust resistant.
Straight oils: These are mainly mineral and extreme pressure (EP) cutting oils. They are used undiluted for slow heavy-cutting operations, as they process good lubricating properties.
Water-base fluids: These are solutions of salts and other minerals in water. They have good cooling properties. They are best applied by using a point, an oil tray and reservoir to give a slow continuous stream over the cutting action. An oil pipe can be used where pumping devices are not possible.
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