Hammers and Mallets
Figure 11-1 shows some of the hammers that the aviation mechanic may be required to use. Metal head hammers are usually sized according to the weight of the head alone without the handle.
Occasionally, it is necessary to use a soft-faced hammer, which has a striking surface made of wood, brass, lead, rawhide, hard rubber, or plastic. These hammers are intended for use in forming soft metals and striking surfaces that are easily damaged. Soft-faced hammers should not be used for striking punch heads, bolts, or nails, as using one in this fashion quickly ruins this type of hammer.
A mallet is a hammer-like tool with a head made of hickory, rawhide, or rubber. It is handy for shaping thin metal parts without causing creases or dents with abrupt corners. Always use a wooden mallet when pounding a wood chisel or a gouge.
When using a hammer or mallet, choose the one best suited for the job. Ensure that the handle is tight. When striking a blow with the hammer, use the forearm as an extension of the handle. Swing the hammer by bending the elbow, not the wrist. Always strike the work squarely with the full face of the hammer. When striking a metal tool with a metal hammer, the use of safety glasses or goggles is strongly encouraged. Always keep the faces of hammers and mallets smooth and free from dents, chips, or gouges to prevent marring of the work.
The screwdriver can be classified by its shape, type of blade, and blade length. [Figure 11-2] It is made for only one purpose, loosening or tightening screws or screw head bolts. When using the common screwdriver, select the largest screwdriver whose blade makes a good fit in the screw that needs to be turned.
A common screwdriver must fill at least 75 percent of the screw slot. If the screwdriver is the wrong size, it cuts and burrs the screw slot, making it unusable. The damage may be so severe that the use of a screw extractor may be required. A screwdriver with the wrong size blade may slip and damage adjacent parts of the structure as well.
The common screwdriver is used only where slotted head screws or fasteners are found on aircraft. An example of a fastener that requires the use of a common screwdriver is the camlock style fastener that is used to secure the cowling on some aircraft.
The two types of recessed head screws for common use are the Phillips and the Reed & Prince. Both the Phillips and Reed & Prince recessed heads are optional on several types of screws. As shown in Figure 11-2, the Reed & Prince recessed head forms a perfect cross. The screwdriver used with this screw is pointed on the end. Since the Phillips screw has a slightly larger center in the cross, the Phillips screwdriver is blunt on the end. The Phillips screwdriver is not interchangeable with the Reed & Prince. The use of the wrong type of screwdriver results in mutilation of the screwdriver and the screw head. When turning a recessed head screw, use only the proper recessed head screwdriver of the correct size. The most common crosspoint screwdrivers are the Number 1 and Number 2 Phillips. Each of these are designed to be used for specific sized screws. A Number 1 Phillips screwdriver is used on 2, 3, and 4 screws, while a Number 2 Phillips is used for screw sizes 5, 6, 7, 8, and 9.
An offset screwdriver may be used when vertical space is limited. Offset screwdrivers are constructed with both ends bent 90° to the shank handle. By using alternate ends, most screws can be seated or loosened even when the swinging space is limited. Offset screwdrivers are made for both standard and recessed head screws. Ratcheting right angle screwdrivers are also available and often prove to be indispensable when working in close quarters.
A screwdriver should not be used for chiseling or prying. Do not use a screwdriver to check an electric circuit since an electric arc will burn the tip and make it ineffective. In some cases, an electric arc may fuse the blade to the unit being checked, creating a short circuit.
When using a screwdriver on a small part, always hold the part in the vise or rest it on a workbench. Do not hold the part in the hand, as the screwdriver may slip and cause serious personal injury.
Replaceable tip screwdrivers, commonly referred to as “10 in 1” screwdrivers, allow for the quick changing of a screwdriver tip and economical replacement of the tip when it becomes worn. A wide variety of screwdriver tips, including flat, crosspoint (Reed & Prince, Phillips), Torx (6-point star-shaped pattern), and square drive tips are available for use with the handles. [Figure 11-3]
The cordless hand-held power screwdriver has replaced most automatic or spiral screwdrivers for the removal of multiple screws from an airframe. Care must be exercised when using a power screwdriver. If the slip clutch is set for too high a setting when installing a screw, the screwdriver tip will slip and rotate on top of the screw head, damaging it. The screw should be started by hand to avoid driving the screw into the nut or nut plate in a cross-threaded manner. To avoid damaging the slot or receptacle in the head of the screw, the use of cordless power drills fitted with a removable tip driver to remove or install screws is not recommended, as the drill does not have a slip-clutch installed.
Pliers and Plier-Type Cutting Tools
As shown in Figure 11-4, the pliers used most frequently in aircraft repair work are the diagonal, needlenose, and duckbill. The size of pliers indicates their overall length, usually ranging from 5 to 12 inches.
Roundnose pliers are used to crimp metal. They are not made for heavy work because too much pressure springs the jaws, which are often wrapped to prevent scarring the metal.
Needlenose pliers have half round jaws of varying lengths. They are used to hold objects and make adjustments in tight places.
Duckbill pliers resemble a “duck’s bill” in that the jaws are thin, flat, and have the shape of a duck’s bill. They are used exclusively for twisting safety wire.
Diagonal pliers are usually referred to as diagonals or “dikes.” The diagonal is a short-jawed cutter with a blade set at a slight angle on each jaw. This tool can be used to cut wire, rivets, small screws, and cotter pins, besides being practically indispensable in removing or installing safety wire. The duckbill pliers and the diagonal cutting pliers are used extensively in aviation for the job of safety wiring.
Two important rules for using pliers:
- Do not make pliers work beyond their capacity. The long-nosed variety is especially delicate. It is easy to spring or break them or nick the edges. If this occurs, they are practically useless.
- Do not use pliers to turn nuts. In just a few seconds, a pair of pliers can damage a nut more than years of service.
Punches are used to locate centers for drawing circles, to start holes for drilling, to punch holes in sheet metal, to transfer location of holes in patterns, and to remove damaged rivets, pins, or bolts.
Solid or hollow punches are the two types generally used. Solid punches are classified according to the shape of their points. Figure 11-5 shows several types of punches.
Prick punches are used to place reference marks on metal. This punch is often used to transfer dimensions from a paper pattern directly on the metal. To do this, first place the paper pattern directly on the metal. Then go over the outline of the pattern with the prick punch, tapping it lightly with a small hammer and making slight indentations on the metal at the major points on the drawing. These indentations can then be used as reference marks for cutting the metal. A prick punch should never be struck a heavy blow with a hammer because it may bend the punch or cause excessive damage to the material being worked.
Large indentations in metal, which are necessary to start a twist drill, are made with a center punch. It should never be struck with enough force to dimple the material around the indentation or to cause the metal to protrude through the other side of the sheet. A center punch has a heavier body than a prick punch and is ground to a point with an angle of about 60°.
The drive punch, which is often called a tapered punch, is used for driving out damaged rivets, pins, and bolts that sometimes bind in holes. The drive punch is therefore made with a flat face instead of a point. The size of the punch is determined by the width of the face, which is usually 1⁄8 inch to 1⁄4 inch.
Pin punches, often called drift punches, are similar to drive punches and are used for the same purposes. The difference between the two is that the sides of a drive punch taper all the way to the face while the pin punch has a straight shank. Pin punches are sized by the diameter of the face, in thirty-seconds of an inch, and range from 1⁄16 to 3⁄8 inch in diameter.
In general practice, a pin or bolt that is to be driven out is usually started and driven with a drive punch until the sides of the punch touch the side of the hole. A pin punch is then used to drive the pin or bolt the rest of the way out of the hole. Stubborn pins may be started by placing a thin piece of scrap copper, brass, or aluminum directly against the pin and then striking it with a hammer until the pin begins to move.
Never use a prick punch or center punch to remove objects from holes because the point of the punch spreads the object and causes it to bind even more.
The transfer punch is usually about 4 inches long. It has a point that tapers and then turns straight for a short distance in order to fit a drill locating hole in a template. The tip has a point similar to that of a prick punch. As its name implies, the transfer punch is used to transfer the location of holes through the template or pattern to the material.