CUTTING TOOLS

Various types of HAND SNIPS/HAND SHEARS are used for cutting and notching sheet metal. Hand snips are necessary because the shape, construction, location, and position of the work to be cut frequently prevents the use of machine-cutting tools.

Hand snips are divided into two groups. Those for straight cuts are as follows: straight snips, combination snips, bulldog snips, and compound lever shears. Those for circular cuts are as follows: circle, hawk's bill, aviation, and Trojan snips. These snips are shown in figure 2-15. The following is a brief description of each type of snip.

STRAIGHT SNIPS (fig. 2-15, view A) have straight jaws for straight line cutting. To ensure strength, they are not pointed. These snips are made in various sizes and the jaws may vary from 2 to 4 1/2 inches. The overall length will also vary from 7 to 15 3/4 inches. The different size snips are made to cut different thicknesses of metal with 18 gauge steel as a minimum for the larger snips. These snips are available for right- or left-hand use.

COMBINATION SNIPS (fig. 2-15, view B) have straight jaws for straight cutting but the inner faces of the jaws are sloped for cutting curves as well as irregular shapes. These snips are available in the same sizes and capacities as straight snips.

BULLDOG SNIPS (fig. 2-15, view C) are of the combination type, They have short cutting blades with long handles for leverage. The blades are inlaid with special alloy steel for cutting stainless steel. Bulldog snips can cut 16 gauge mild steel. The blades are 2 1/2 inches long and the overall length of the snip varies from 14 to 17 inches.

COMPOUND LEVER SHEARS (fig. 2-15, view D) have levers designed that give additional leverage to ease the cutting of heavy material. The lower blade is bent to allow the shears to be inserted in a hole in the bench or bench plate. This will hold the shear in an upright position and make the cutting easier. The cutting blades are removable and can be replaced. The capacity is 12 gauge mild steel. It has cutting blades that are 4 inches long with an overall length of 34 1/2 inches.

CIRCLE SNIPS (fig. 2-15, view E) have curved blades and are used for making circular cuts, as the name implies. They come in the same sizes and capacities as straight snips and either right- or left-hand types are available.

HAWK'S BILL SNIPS (fig. 2-15, view F) are used to cut a small radius inside and outside a circle. The narrow, curved blades are beveled to allow sharp turns without buckling the sheet metal. These snips are useful for cutting holes in pipe, in furnace hoods, and in close quarters work. These snips are available with a 2 1/2-inch cutting edge and have an overall length of either 11 1/2 or 13 inches and have a 20 gauge mild steel capacity.

AVIATION SNIPS (fig. 2-15, view G) have compound levers, enabling them to cut with less effort. These snips have hardened blades that enable them to cut hard material. They are also useful for cutting circles, for cutting squares, and for cutting compound curves and intricate designs in sheet metal. Aviation snips come in three types: right hand, left hand, and straight. On right-hand snips, the blade is on the left and they cut to the left. Left-hand snips are the opposite. They are usually color-coded in keeping with industry standards-green cuts right, red cuts left, yellow cuts straight. Both snips can be used with the right hand. The snips are 10 inches long and have a 2-inch cut and have a 16 gauge mild steel capacity.

TROJAN SNIPS (fig. 2-15, view H) are slim-bladed snips that are used for straight or curved cutting. The blades are small enough to allow sharp turning cuts without buckling the metal. These snips can be used to cut outside curves and can also be used in place of circle snips, hawk's bill snips, or aviation snips when cutting inside curves. The blades are forged high grade steel. These snips come in two sizes: one has a 2 1/2-inch cutting length and a 12-inch overall length and the other has a 3-inch cutting length and a 13-inch overall length, They both have a 20 gauge capacity.

Modern snips are designed to cut freely with a minimum curling of the metal. The snips are generally held in the right hand at right angles to the work (fig, 2-16). Open the blades widely to obtain maximum leverage. Do not permit the ends to close completely at the end of a cut or a rough

Figure 2-15.-Hand snips.

Figure 2-16.-Proper method of cutting with snips.

edge will result. Cut circular sections from the right side (fig. 2-17).

When making internal circular cuts, you make a small opening near the center of the opening, insert the snips, and cut from the upper side, gradually increasing the radius of the cut until the opening is completed (fig. 2-18).

Large sheet-metal sections are cut on SQUARING SHEARS that are discussed later in this chapter.

The COMBINATION NOTCHER, COPER, and SHEAR (fig. 2-19) is ideal for notching corners or the edge of sheet metal. The blades are adjustable for conventional notching or for piercing, starting inside the blank.

PORTABLE POWER SHEARS make it possible to do production work. They are designed to do straight or circular cutting (fig. 2-20).

Small diameter openings can be made with a SOLID PUNCH (fig. 2-21) or a HOLLOW PUNCH

Figure 2-17.-Making a circular cut.

Figure 2-19.-Combination notcher, coper, and shear.

(fig. 2-22). Locate the position of the hole; select the correct size punch and hammer; then place the metal section on a lead cake or on the end grain of a block of hard wood (fig. 2-23). Strike the punch firmly with

the hammer. Turn the punched section over so the burred section is up, then smooth it with a mallet.

FOOT-ACTUATED SQUARING SHEARS (fig. 2-24) make it possible to square and trim large sheets. Do not attempt to cut metal heavier than the designed capacity of the shears. The maximum capacity of the machine is stamped on the manufacturer's

Figure 2-24.-Foot-actuated squaring shears.

specification plate on the front of the shears. Check the gauge of the metal against this size with a SHEET-METAL GAUGE (fig. 2-25). This figure shows the gauge used to measure the thickness of metal sheets. The gauge is a disc-shaped piece of metal, having slots of widths that correspond to the U.S. gauge numbers from 0 to 36. Each gauge number is marked on the front and the corresponding decimal equivalent marked on the back.

Do NOT cut wire, band iron, or steel rods with the squaring shears.

Figure 2-23.-Correct method of backing sheet metal for making a hole with a punch.

Figure 2-25.-Sheet-metal guage.

The length of the cut is determined by the position of the BACK GAUGE when the metal is inserted from the front of the shears. The FRONT GAUGE controls the length of the cut when the metal sheet is inserted from the rear. The front gauge is seldom used and is usually removed from the shears. A BEVEL GAUGE permits angular cuts to be made.

To make a cut, set the back gauge to the required dimension by using the graduated scale on the top of the extension arms or on the graduated section on the bed top. Hold the piece firmly against the SIDE GAUGE with both hands until the HOLD-DOWN comes into position, and apply pressure to the FOOT PEDAL.

NOTE: KEEP HANDS CLEAR OF THE BLADE AND FEET FROM BENEATH THE FOOT PEDAL. RING AND CIRCULAR SHEARS (fig. 2-26) are intended for cutting inside and outside circles in sheet metal. The CLAMPING HEAD is positioned for the desired diameter and the blank is inserted. Lower the CUTTING DISC and make the cut.

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