Lesson Notes By Weeks and Term - Junior Secondary School 3
INTRODUCTION TO MACHINE TOOLS
INTRODUCTION TO MACHINE TOOLS
TERM: 2ND TERM
SUBJECT: BASIC TECH
CLASS: JSS 3
Reference Materials
WEEK 2
TOPIC: INTRODUCTION TO MACHINE TOOLS
CONTENT
Definition
Machine tools are machines used for metal work operation. There are five basic machine tools. This includes the following:
Evaluation
The milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines. Unlike a drill press, which holds the workpiece stationary as the drill moves axially to penetrate the material, milling machines also move the workpiece radially against the rotating milling cutter, which cuts on its sides as well as its tip. Workpiece and cutter movement are precisely controlled to less than 0.001 in (0.025 mm), usually by means of precision ground slides and leadscrews or analogous technology. Milling machines may be manually operated, mechanically automated, or digitally automated via computer numerical control (CNC).
Milling machines can perform a vast number of operations, from simple (e.g., slot and keyway cutting, planing, drilling) to complex (e.g., contouring, diesinking). Cutting fluid is often pumped to the cutting site to cool and lubricate the cut and to wash away the resulting swarf.
Planing machine (Planer)
Metal-cutting machine tool in which the work piece is firmly attached to a horizontal table that moves back and forth under a single-point cutting tool. The tool-holding device is mounted on a cross rail so that the tool can be moved across the table in small sideward movements. Since the cutting tool can be moved at almost any angle, a wide variety of grooves and surfaces can be generated. Mechanical planers, or surfacers, are also used to smooth wood to an even thickness. Planers perform the same operations as shapers but can machine work pieces up to 50 ft (15 m) long.
A machine for the shaping of long, flat, or flat contoured surfaces by reciprocating the work piece under a stationary single-point tool or tools.
Milling machine
This is a machine tool that rotates a circular tool with numerous cutting edges arranged symmetrically about its axis, called a milling cutter. The metal work piece is usually held in a vise clamped to a table that can move in three perpendicular directions. Cutters of many shapes and sizes are available for a wide variety of milling operations. Milling machines cut flat surfaces, grooves, shoulders, inclined surfaces, dovetails, and T-slots. Various form-tooth cutters are used for cutting concave forms and convex grooves, for rounding corners, and for cutting gear teeth.
A machine for the removal of metal by feeding a work piece through the periphery of a rotating circular cutter. It is known as miller.
The drill press
This is m machine tool for producing holes in hard substances. The drill is held in a rotating spindle and is fed into the work piece, which is usually clamped in a vise supported on a table. The drill may be gripped in a chuck with three jaws that move radially in unison, or it may have a tapered shank that fits into a tapered hole in the spindle. Means are provided for varying the spindle speed and (on some machines) for automatically feeding the drill into the work piece. See also boring machine. A drilling machine, in which a vertical drill, moves into the work, which is stationary.
The lathe machine
Lathe (lÄth), machine tool for holding and turning metal, wood, plastic, or other material against a cutting tool to form a cylindrical product or part. It also drills, bores, polishes, grinds, makes threads, and performs other operations. Its principal parts are the headstock (attached to the bed or base of the machine), which holds one end of the material in a rotating spur; the tailstock, which holds the other end, moves along the bed, and can be clamped in position at any point; the cutting tool; and the power feed, comprising the drive and its motive parts.
Machine tool that performs turning operations in which unwanted material is removed from a work piece rotated against a cutting tool. Lathes are among the oldest and most important machine tools, used in France from 1569 and important in the Industrial Revolution in England, when they were adapted for metal cutting. Lathes (usually called engine lathes) today has a power-driven, variable-speed horizontal spindle to which the work holding device is attached. Operations include turning straight or tapered cylindrical shapes, grooves, shoulders, and screw threads and facing flat surfaces on the ends of cylindrical parts. Internal cylindrical operations include most of the common hole-machining operations, such as drilling, boring, reaming, counter boring, countersinking, and threading with a single-point tool or tap. See also boring machine.
Lathe: A machine for shaping, boring, facing, or cutting a screw thread in metal, wood, etc., in which the work piece is turned about a horizontal axis against a fixed tool
The lathe machine is regarded as the father of all machine tools because apart from being used for turning cylindrical surface (external and internal) it can perform other operations which are peculiar to other machines.
Thus, it is possible to carry out the following operations on the lathe machine:
Parts of the lathe machine
Wood holding methods
Work holding methods on a lathe machine include:
SHAPER
A shaper is analogous to a planer, but smaller, and with the cutter riding a ram that moves above a stationary workpiece, rather than the entire workpiece moving beneath the cutter. The ram is moved back and forth typically by a crank inside the column; hydraulically actuated shapers also exist.
Operation
Shaper linkage. Note the drive arm revolves less for the return stroke than for the cutting stroke, resulting in a quicker return stroke and more powerful cutting stroke.
A shaper operates by moving a hardened cutting tool backwards and forwards across the workpiece. On the return stroke of the ram the tool is lifted clear of the workpiece, reducing the cutting action to one direction only.
The workpiece mounts on a rigid, box-shaped table in front of the machine. The height of the table can be adjusted to suit this workpiece, and the table can traverse sideways underneath the reciprocating tool, which is mounted on the ram. Table motion may be controlled manually, but is usually advanced by an automatic feed mechanism acting on the feedscrew. The ram slides back and forth above the work. At the front end of the ram is a vertical tool slide that may be adjusted to either side of the vertical plane along the stroke axis. This tool-slide holds the clapper box and toolpost, from which the tool can be positioned to cut a straight, flat surface on the top of the workpiece. The tool-slide permits feeding the tool downwards to deepen a cut. This adjustability, coupled with the use of specialized cutters and toolholders, enable the operator to cut internal and external gear tooth profiles, splines, dovetails, and keyways.
The ram is adjustable for stroke and, due to the geometry of the linkage, it moves faster on the return (non-cutting) stroke than on the forward, cutting stroke. This action is via a slotted link or whitworth link.
USES
The most common use is to machine straight, flat surfaces, but with ingenuity and some accessories a wide range of work can be done. Other examples of its use are:
Evaluation
Reading Assignment
Read “MACHINE TOOLS”
Reference Materials
Weekend Assignment
Theory
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