Sawing is one of the most important cuttings off operations performed in a manufacturing plant. Metal sawing is chiefly concerned with cutting bar stock to a convenient length or size for machining.
In sawing, the individual teeth of the saw “track” through the work, in each tooth deepening the cut made by the preceding tooth in the direction of feed. Either the saw or the work may be fed and, by controlling the direction of feed, either straight or curved cut can be produced. The width of the cut is approximately equal to the width of the saw itself.
Classification of Sawing Machine
Sawing machines may be classified by the motion used for the cutting action. Accordingly, the various types of power sawing machine are listed below.
1. Reciprocating saw.
a) Horizontal sawing machine. b) Vertical sawing machine.
2. Circular saw.
a) Cold saw b) Friction disk c) Abrasive disk
3. Band saw.
a) Contour band saw. b) Friction blade.
Power hacksaws represent reciprocating saws. A power hacksaw consists of a saw frame, a means for reciprocating the saw and frame, a worktable and vise, a supporting base and a source of power. In operation, the machine drives a blade back and forth through a work piece, pressing down on the cutting stroke and releasing the pressure on the return. The down feed force on the blade may be obtained from gravity or springs regulated by a ratchet mechanism; a positive feed screw of from a hydraulic drive. The simplest type of feed is the gravity feed in which the saw blade is forced into the work by the weight of the saw and frame. A hydraulic or mechanical arrangement is also incorporated for lifting the blade on the return stroke. Many are crank driven; the large ones often are hydraulically driven.
The stock to be cut is held between the clamping saws. Several pieces of bar stock can be clamped together and cut at the same time. Both square and angular cuts can be made.
Circular saws are cut by means of a revolving disc. The disc may have large teeth or almost no teeth. Machines of this type are divided into three classifications as given before.
The cold saw has a circular blade with inserted teeth for cutting small or large bars to length. It cuts very rapidly because of the large diameter blades, but it, runs at relatively slow speed and is very powerful. The cut made is very smooth and accurate. Coolants may or may not be used with this typed of saw. Average thickness of the cut is 6 mm. A cold saw can be equipped with automatic bar-feeding mechanisms. The stock is held in a vise capable of handling one or a number of parts at the same time.
Friction discs are circular blades having almost no teeth. They operate at thigh speeds and generate heat. The heat of friction softens the metal of the woekpiece in contact with the disc, and the soft metal is rubbed away. Friction sawing is fast but leaves a heavier burr and a less accurate surface than cutting tooth does.
Abrasive disc, as the name implies, are thin flexible grinding wheels. Thin resionoid or rubber-bonded wheels rotating at high speeds are generally used. The cutting action is fast and accurate but this abrasive disc cutting is not a true sawing technique.
In band saw, a continuous saw blade or band runs over the rims of two wheels, one of which drives the saw at the desired cutting speed. The work is mounted on the table between the two wheels. In contrast to the reciprocating action of the hacksaw, which is idle on the return stroke, the band saw is never idle. This continuous cutting action makes the band saw more productive. They are mainly divided into two classifications as given before.
The contour band saw is the most versatile of all types of sawing machines in application. The work may be fed in any direction on the table, and the direction of feed is readily controlled and changed while cutting is in process to produce any desired outline. These machines are widely used for making dies or other parts with a contour internal shape.
A friction band saw operates on the same principle as the friction circular saw. The dull blade produces great friction and the kerf of the teeth removes small, softened particles of the work.
Selecting A Blade For Sawing Machine
Blade materials include standard carbon steel, high-speed steel and bimetallic high-speed steel. There are three tooth sets that can be used; raker, alternate and wavy fig. Shows these tooth sets, there are tooth forms also shown in fig. three tooth forms; standard, skip and hook.