There are several kinds of hand snips, each of which serves a different purpose. Straight, curved, hawksbill, and aviation snips are in common use. Straight snips are used for cutting straight lines when the distance is not great enough to use a squaring shear and for cutting the outside of a curve. The other types are used for cutting the inside of curves or radii. Snips should never be used to cut heavy sheet metal. [Figure 11-13]
Aviation snips are designed especially for cutting heat-treated aluminum alloy and stainless steel. They are also adaptable for enlarging small holes. The blades have small teeth on the cutting edges and are shaped for cutting very small circles and irregular outlines. The handles are the compound leverage type, making it possible to cut material as thick as 0.051 inch. Aviation snips are available in two types: those which cut from right to left and those which cut from left to right.
Unlike the hacksaw, snips do not remove any material when the cut is made, but minute fractures often occur along the cut. Therefore, cuts should be made about 1⁄32 inch from the layout line and finished by hand filing down to the line.
The common hacksaw has a blade, a frame, and a handle. The handle can be obtained in two styles: pistol grip and straight. [Figure 11-14]
Hacksaw blades have holes in both ends; they are mounted on pins attached to the frame. When installing a blade in a hacksaw frame, mount the blade with the teeth pointing forward, away from the handle.
Blades are made of high-grade tool steel or tungsten steel and are available in sizes from 6 to 16 inches in length. The 10-inch blade is most commonly used. There are two types: the all-hard blade and the flexible blade. In flexible blades, only the teeth are hardened.
Selection of the best blade for the job involves finding the right type and pitch. An all-hard blade is best for sawing brass, tool steel, cast iron, and heavy cross-section materials. A flexible blade is usually best for sawing hollow shapes and metals having a thin cross-section.
The pitch of a blade indicates the number of teeth per inch. Pitches of 14, 18, 24, and 32 teeth per inch are available. A blade with 14 teeth per inch is preferred when cutting machine steel, cold-rolled steel, or structural steel. A blade with 18 teeth per inch is preferred for solid stock aluminum, bearing metal, tool steel, and cast iron. Use a blade with 24 teeth per inch when cutting thick-walled tubing, pipe, brass, copper, channel, and angle iron. Use the 32 teeth per inch blade for cutting thin-walled tubing and sheet metal. When using a hacksaw, observe the following procedures:
- Select an appropriate saw blade for the job.
- Assemble the blade in the frame so that the cutting edge of the teeth points away from the handle.
- Adjust tension of the blade in the frame to prevent the saw from buckling and drifting.
- Clamp the work in the vise in such a way that provides as much bearing surface as possible and engages the greatest number of teeth.
- Indicate the starting point by nicking the surface with the edge of a file to break any sharp corner that might strip the teeth. This mark also aids in starting the saw at the proper place.
- Hold the saw at an angle that keeps at least two teeth in contact with the work at all times. Start the cut with a light, steady, forward stroke just outside the cutting line. At the end of the stroke, relieve the pressure and draw the blade back. (The cut is made only on the forward stroke.)
- After the first few strokes, make each stroke as long as the hacksaw frame allows. This prevents the blade from overheating. Apply just enough pressure on the forward stroke to cause each tooth to remove a small amount of metal. The strokes should be long and steady with a speed not more than 40 to 50 strokes per minute.
- After completing the cut, remove chips from the blade, loosen tension on the blade, and return the hacksaw to its proper place.
A chisel is a hard steel cutting tool that can be used for cutting and chipping any metal softer than the chisel itself. It can be used in restricted areas and for such work as shearing rivets, or splitting seized or damaged nuts from bolts. [Figure 11-15] The size of a flat cold chisel is determined by the width of the cutting edge. Lengths vary, but chisels are seldom under 5 inches or over 8 inches long.
Chisels are usually made of eight-sided tool steel bar stock, carefully hardened and tempered. Since the cutting edge is slightly convex, the center portion receives the greatest shock when cutting, and the weaker corners are protected. The cutting angle should be 60° to 70° for general use, such as for cutting wire, strap iron, or small bars and rods. When using a chisel, hold it firmly in one hand. With the other hand, strike the chisel head squarely with a ball peen hammer.
When cutting square corners or slots, a special cold chisel called a cape chisel should be used. It is like a flat chisel except the cutting edge is very narrow. It has the same cutting angle and is held and used in the same manner as any other chisel.
Rounded or semicircular grooves and corners that have fillets should be cut with a round-nose chisel. This chisel is also used to re-center a drill that has moved away from its intended center.
The diamond point chisel is tapered square at the cutting end, and then ground at an angle to provide the sharp diamond point. It is used for cutting B-grooves and inside sharp angles.
Most files are made of high-grade tool steels that are hardened and tempered. Files are manufactured in a variety of shapes and sizes. They are known either by the cross section, the general shape, or by their particular use. The cuts of files must be considered when selecting them for various types of work and materials.
Files are used to square ends, file rounded corners, remove burrs and slivers from metal, straighten uneven edges, smooth rough edges, and file holes and slots.
Files have three distinguishing features:
- Their length, measured exclusive of the tang [Figure 11-16];
- Their kind or name, such as a hand file shown in Figure 11-16, that has reference to the relative coarseness of the teeth; and
- Their cut, such as a single- or double-cut file.
Files are usually made in two types of cuts: single cut and double cut. The single cut file has a single row of teeth extending across the face at an angle of 65° to 85° with the length of the file. The size of the cuts depends on the coarseness of the file. The double cut file has two rows of teeth that cross each other. For general work, the angle of the first row is 40° to 45°. The first row is generally referred to as “overcut,” and the second row as “upcut;” the upcut is somewhat finer than and not as deep as the overcut.
Care and Use
Files and rasps are catalogued in three ways:
- Length—Measuring from the tip to the heel of the file. The tang is never included in the length.
- Shape—Refers to the physical configuration of the file (circular, rectangular, triangular, or a variation thereof).
- Cut—Refers to both the character of the teeth or the coarseness—rough, coarse, and bastard for use on heavier classes of work and second cut, smooth, and dead smooth for finishing work.
Most Commonly Used Files
These are parallel in width and tapered in thickness. They have one safe edge (smooth edge) that permits filing in corners and on other work where a safe edge is required. Hand files are double cut and used principally for finishing flat surfaces and similar work. [Figure 11-17]
These files are slightly tapered toward the point in both width and thickness. They cut on both edges, as well as on the sides. They are the most common files in use. Flat files are double cut on both sides and single cut on both edges. [Figure 11-17]
These are usually tapered slightly in thickness and in width for about one-third of their length. The teeth are ordinarily single cut. These files are used for draw filing and to some extent for filing soft metals. [Figure 11-17]
These files may be tapered or blunt and are double cut. They are used principally for filing slots and key seats and for surface filing. [Figure 11-17]
Round or Rattail Files
These are circular in cross section and may be either tapered or blunt and single or double cut. They are used principally for filing circular openings or concave surfaces. [Figure 11-17]
Triangular and Three Square Files
These files are triangular in cross section. Triangular files are single cut and are used for filing the gullet between saw teeth. Three square files, which are double cut, may be used for filing internal angles, clearing out corners, and filing taps and cutters. [Figure 11-17]
These files cut on both the flat and round sides. They may be single or double cut. Their shape permits them to be used where other files would be unsatisfactory. [Figure 11-17]
These are especially designed for use on soft metals. They are single cut and are made in various lengths. [Figure 11-17]
Rectangular in section and tapers to narrow point in width. This file is used for narrow space filing where other files cannot be used. [Figure 11-17]
Knife blade section. This file is used by tool and die makers on work having acute angles. [Figure 11-17]