JSS 2 SECOND TERM BASIC TECH Week 11
Topic: CUTTING TOOLS
The tools used in cutting metal include chisels, files and saws.
a. Chisels
Chisels are made of octagonal tool steel. They are forged to shape, filed, hardened and tempered. They are called cold chisels because they are used to cut cold metals. There are four main types.
i. Flat chisel
It is used for general purpose, cutting sheet and plate metal and removing surplus metal from surfaces.
ii. Cross out chisel
It is used for cutting square grooves such as slot, channels and key-ways.
iii. Half-round chisel
In the case, the cutting edge is ground half-round. It is used for cutting grooves and for drawing over the centres of holes that have run off during drilling.
iv. Diamond point chisel
This chisel is drawn down to a square section. The end is ground off at an angle and this produces the diamond shape. It is used for squaring holes and clearing corners.
b. Files
Files are made of cast steel. The blade is hardened and tempered but the tang is soft. Files are classified according to their cut, shape and length.
I. The cut
The cut of the file refers to the teeth. The teeth may be single-cut or double-cut. It is used when a fair amount of metal requires removing. It could also be used for finishing or when working to fine limits. Then the cuts will be smooth or dead-smooth.
Needle or Swiss files
Needle files are used for very fine work. Handles are not required because the end is curled to form a grip. It comes in different shapes.
Riffler files
These are used for engraving, die sinking and silver smiting. They are mainly used for filing intricate shapes.
Abrafile
An abrafile is a file but it is used as a saw. It is circular in cross-section like a piece of wire of about 1.5mm diameter. It has teeth all round its circumference. It is normally fitted into an abrafile frame or hacksaw frame. It is useful for sawing profiles.
Round or rat-tail file
This tapers for the last third of its length.
Triangular or three square file
This is an equilateral triangle in cross-section. It tapers towards the tip.
Knife file
This resembles the blade of a knife and is useful for cleaning corners.
II. Shape
There are six shapes for the files
Hand flat file
This is parallel with but tapers in thickness slightly for the last two shuds. One edge is without teeth. This is called the safe edge.
Flat file
This has the last two thirds paper in width and thickness. It also has teeth on both edges.
Pillar file
In its own case is narrower. It tapers in thickness slightly for the last two thirds. Only one edge has teeth.
Warding file
This is to flat the file but it is thinner. It is used by locksmiths.
Half-round file
It has one flat and one curved surface. The curved surface is single cut.
Square file
It is our on all four sides and tapers towards the tip.
c. Saws
There are a number of saw used for cutting metals in the workshop. They include:
i. Hacksaw
The replaceable blade of the hacksaw is held in tension in an adjustable frame. The blades have various widths, lengths and thickness, but the common ones are 250 or 300mm long and 13mm wide and 0.65mm thick. They are made of high steel or low-tungsten steel.
ii. Junior hacksaw
The junior hacksaw is used for fine work. The blade is held under tension by the natural spring in the frame.
iii. Brass back-saw
This saw is used for fine work in soft metals. The blade is supported along its length and this enables it to produce a straight cut. New blades can be inserted.
Piercing saw
An adjustable frame allows a very fine blade to be held in a clamp-like grip and tension. The saw is useful for curved work can be passed through a hole for pierced work.
