Wing jack pad assembly FIGURE 11-41. Jacking a complete aircraft.
Prior to jacking, determine if the aircraft configuration will permit jacking. There may be equipment or fuel which has to be removed if serious structural damage is to be avoided during jacking. If any other work is in progress on the aircraft, ascertain if any critical panels have been removed. On some aircraft the stress panels or plates must be in place when the aircraft is jacked to avoid structural damage.
Extend the jacks until they contact the jack pads. A final check for alignment of the jacks should be made before the aircraft is raised, since most accidents during jacking are the result of misalined jacks.
When the aircraft is ready to be raised, a man should be stationed at each jack. The jacks should be operated simultaneously to keep the aircraft as level as possible and to avoid overloading any of the jacks. This can be accomplished by having the crew leader stand in front of the aircraft and give instructions to the men operating the jacks.
Figure 11-41 shows an aircraft being jacked.
Caution should be observed, since on many jacks the piston can be raised beyond the safety point;
therefore, never raise an aircraft any higher than is necessary to accomplish the job.
The area around the aircraft should be secured while the aircraft is on jacks. Climbing on the aircraft should be held to an absolute minimum, and no violent movements should be made by persons who are required to go aboard. Any cradles or necessary supports should be placed under the fuselage or wings of the aircraft at the earliest possible time, particularly if the aircraft is to remain jacked for any length of time.
On collet-equipped jacks, the collet should be kept within two threads of the lift tube cylinder during raising, and screwed down firmly to the cylinder after jacking is completed to prevent settling.
Before releasing jack pressure and lowering the aircraft, make certain that all cribbing, workstands, equipment, and persons are clear of the aircraft, that the landing gear is down and locked, and that all ground locking devices are properly installed.
Jacking One Wheel of an Aircraft When only one wheel has to be raised to change a tire or to grease wheel bearings, a low single-base jack is used. Before the wheel is raised, the remaining wheels must be chocked fore and aft to prevent movement of the aircraft. If the aircraft is equipped with a tailwheel, it must be locked. The wheel should be raised only high enough to clear the concrete surface. Figure 11-42 shows a wheel being raised using a single-base jack.
COLD WEATHER SUGGESTIONS When an aircraft is to be exposed to extreme cold for any length of time, extra care should be taken to see that the aircraft is prepared for winter. All covers for engines, air-conditioning system intakes, pitot and static system openings, and ram air inlets should be installed to prevent snow and ice accumulations. Small covers should be conspicuously marked or tagged so that they are not likely to be overlooked betore flight.
If the aircraft is to be parked in snow or ice 525
Main landing gear jack pad Nose landing gear jack pad FIGURE 11-42. Jacking one wheel.
conditions, it sometimes saves time and man-hours to paint around doors and frequently opened access panels with one of the inhibited glycol antifreeze compounds. The glycol may be painted on surfaces under snow covers to prevent the cover freezing to the surface. It can also be used full strength on wing or tail surfaces themselves to prevent frost. However, if snow is expected, painting exposed surfaces is rarely useful, since the slush that forms will be more troublesome than dry snow.
Another timesaver can be parking the wheels on planking rather than on ice or packed snow, or when sleet or slush may be expected to freeze tires to the ground. Sand can be used for such a purpose but should be confined to wheel areas and not distributed where it may be drawn into the engines on starting.
Flaps and spoilers should be retracted. Aircraft with movable horizontal stabilizers should have them set at approximately zero. All water and waste systems should be drained or serviced with an antifreeze solution when applicable.
If an aircraft is to be parked for a long period of time, leaving a window partially open will permit circulation of the air inside and help prevent frosting of the windows. The best way to remove snow is to sweep off as much as possible. One method is to throw a line over the fuselage and drag the snow off. A brush or broom can be used on wing and tail surfaces. Do not damage vortex generators on aircraft that have them.
A certain amount of snow may freeze to the aircraft surfaces which cannot be brushed off. It is important that all surfaces are entirely free of ice, snow, or frost before takeoff.
Most commercial facilities have spray equipment for applying deicing fluids, which are usually diluted with water and sometimes heated. Glycol antifreeze compounds, often identified by military specification numbers, have been materially improved. The compound recommended for commercial use is MIL-A-8243A. This is ethylene glycol and propylene glycol in approximately 3:1 ratio, with added corrosion inhibitor and a wetting agent. It has low toxicity, causes no damage to aircraft metals, and has no effect on most plastics, paint, or rubber.
If hot air is used for deicing, particularly from a ground starter unit, skin areas should not be overheated. A large flow of warm air is more effective than a blast of hot air. Any temperature under the boiling point of water is safe.
Should the last layer of ice or snow be melted from the fuselage, or from the leading edges of the wing, by internal heating from ground sources, the water will probably run down and refreeze in unheated areas, and must be removed again.
Whatever the deicing method, inspect the trailing edge mechanism areas of the wing and tail to be sure that water or slush has not run down inside to refreeze.
When conditions warrant, preheating is used on the following sections or parts of the aircraft:
accessory section, nose section, Y-drain valve, all oil lines, oil tank sump, starters, instruments, tires, cockpits, and elevator trim tabs.
Check all drain valves, oil tank sumps, oil drains, fuel strainers, vent lines, and all main and 526
auxiliary control hinges and surfaces, for the existence of ice or hard snow. Thoroughly check all deicing equipment to ensure proper operation.
Alcohol tanks must be checked for proper level of deicing alcohol.
The use of an external heater is permissible at temperatures below 0° C. for heating oil and engine(s). If a heater is not available for heating the oil, the oil can be drained, heated, and put back into the system.
When starting a reciprocating engine in cold weather, try to catch the engine on the first starting attempt to prevent ice forming on the spark plugs. If ice should form, remove the spark plugs, bake, and reinstall.
In freezing weather, ice may form on the propellers while the engine is warming up. Using the propeller deicer (if available) during warm-up eliminates this condition. The turbine engine should be easier to start in very bad weather than the average piston engine. Turbine engines do not require oil dilution, priming, or lengthy warm-up.
Turbine engine compressor rotors should be checked to see that ice has not formed inside. This is particularly necessary when an engine has shut down in driving rain or snow. Be very careful when running engines if icy conditions exist. With icy pavement, chocks slide very easily, and once the aircraft is in motion it is difficult to stop.
After a flight, the oil is diluted prior to shutdown of reciprocating engines equipped with an oil dilution system, if temperatures near or below freezing are expected before or at the time of the next start. When it is necessary to dilute the oil, consult the manufacturer's instructions for the applicable aircraft. These instructions should be strictly followed; otherwise the engine can be When fueling aircraft, the fuel tanks should be left about 3 to 5 percent below maximum capacity.
This allows for expansion in the event the aircraft is brought into the hangar prior to the next flight.
Fuel expands approximately 1 percent for each 10° C. increase in temperature. If fuel tanks are filled to the normal levels, at a temperature of approximately 0° C. to 10° C., and later brought into a warm hangar (20° C.), the ensuing expansion will overflow the tanks, causing a fire hazard.
Tires should be inflated to load standards, regardless of possible rise in pressure under warmer conditions. Underinflation quickly causes overheat that would result in more tire damage and more possibility of blowout than a slight amount of overinflation. If a tire is frozen to the ground, it should be thawed with warm air or water and, moved before it re-freezes.
It is easy to exceed nose gear towing load limits in snow or slush. If the airplane must be towed in deep snow, it should be pulled by cables attached to the main landing gear lugs.
The aircraft battery should require no special attention other than the normal routine servicing.
CHAPTER 12
HANDTOOLS AND MEASURING DEVICES
INTRODUCTION This chapter contains information on some of the handtools used by an aviation mechanic. It outlines the basic knowledge required in using the most common handtools and measuring instruments used in aircraft repair work. This information, however, cannot replace sound judgment on the part of the individual. There are many times when ingenuity and resourcefulness can supplement the basic rules. A sound knowledge is required of these basic rules and of the situations in which they apply. The use of tools may vary, but good practices for safety, care, and storage of tools remain the same.
GENERAL-PURPOSE TOOLS Hammers and Mallets Figure 12-1 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 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.
Ball peen Straight peen Cross peen Tinners mallet Riveting hammer FIGURE 12-1. Hammers.
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 rough work. Striking punch heads, bolts, or nails will quickly ruin this type hammer.
A mallet is a hammerlike tool with a head made of hickory, rawhide, or rubber. It is handy for shaping thin metal parts without denting them.
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.
Always keep the faces of hammers and mallets smooth and free from dents to prevent marring the work.
The screwdriver can be classified by its shape, type of blade, and blade length. It is made for only one purpose, i.e., for loosening or tightening screws or screwhead bolts. Figure 12-2 shows several different types of screwdrivers. When using the common screwdriver, select the largest screwdriver whose blade will make a good fit in the screw which is 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 worthless. A screwdriver with the wrong size blade may slip and damage adjacent parts of the structures.
The common screwdriver is used only where slotted head screws or fasteners are found on aircraft. An example of a fastener which requires the use of a common screwdriver is the airlock fastener which is used to secure the cowling on some aircraft.
The two types of recessed head screws in common use are the Phillips and the Reed and Prince.
be seated or loosened even when the swinging space is limited. Offset screwdrivers are made for Square shank Common both standard and recessed head screws. 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 useless. In some cases, an electric arc may fuse the blade to the unit being checked.
Screw holding When using a screwdriver on a small part, always driver hold the part in the vise or rest it on a workbench.
Compression of spring holds Do not hold the part in the hand, as the screwscrew firmly against tip of driver. driver may slip and cause serious personal injury.
The ratchet or spiral screwdriver is fast acting in that it turns the screw when the handle is pulled back and then pushed forward. It can be set to turn the screw either clockwise or counterclockwise, Reed & Prince or it can be locked in position and used as a standdriver ard screwdriver. The ratchet screwdriver is not a heavy-duty tool and should be used only for light work. A word of caution: When using a spiral or ratchet screwdriver, extreme care must be used to maintain constant pressure and prevent the blade from slipping out from the slot in the screw head Phillips head driver If this occurs, the surrounding structure is subject to damage.
Offset driver Ratchet and spiral driver FIGURE 12-2. Typicai screwdrivers.
Both the Phillips and Reed and Prince recessed heads are optional on several types of screws. As shown in figure 12-2, the Reed and 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 Philips screwdriver is not interchangeable with the Reed and Prince. The use of the wrong type screwdriver results in mutilation of the screwdriver and the screwhead. When turning a recessed head screw, use only the proper recessed head screwdriver of the correct size.
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 Pliers and Plier Type Cutting Tools There are several types of pliers, but those used most frequently in aircraft repair work are the diagonal, adjustable combination, needlenose, and duckbill. The size of pliers indicates their overall length, usually ranging from 5 to 12 inches.
The 6-inch slip-joint plier, is the preferred size for use in repair work. The slip-joint permits the jaws to be opened wider at the hinge for gripping objects with large diameters. Slip-joint pliers come in sizes from 5 to 10 inches. The better grades are drop-forged steel.
Flatnose pliers are very satisfactory for making flanges. The jaws are square, fairly deep, and usually well matched, and the hinge is firm.
are characteristics which give a sharp, neat bend.
Roundnose pliers are used to crimp metal. They are not made for heavy work because too much pressure will spring 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 shaped like a duck's bill. They are used exclusively for twisting safety wire.
Water pump (channel locks) pliers are slip-joint pliers with the jaws set at an angle to the handles.
The most popular type has the slip-joint channeled, hence the name channel locks. These are used to grasp packing nuts, pipe, and odd shaped parts.
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 indispensible 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 are:
1. Do not make pliers work beyond their ca- The longnosed variety are especially delicate. It is easy to spring or break them, or nick the edges. If this occurs, they are practically useless.
2. Do not use pliers to turn nuts.
few seconds, a pair of pliers can damage a nut more than years of service.
Punches 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.
Genter punch Prick punch Starting punch Pin punch Aligning punch Hollow shank gasket punch FIGURE 12-3. Punches.
Solid or hollow punches are the two types generally used. Solid punches are classified according to the shape of their points. Figure 12-3 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, that 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 which 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 ⅛ inch to ¼ inch.
Pin punches, often called drift punches, are similar to drive punches and are used for the same purposes. The difference in 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 16 to 8 inch in diameter.
In general practice, a pin or bolt which 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 531
punch will spread the object and cause it to bind even more.
The transfer punch is usually about 4 inches long. It has a point that tapers, 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.
Wrenches The wrenches most often used in aircraft maintenance are classified as open-end, box-end, socket, adjustable, and special wrenches. The allen wrench, although seldom used, is required on one special type of recessed screw. One of the most widely used metals for making wrenches is chromevanadium steel. Wrenches made of this metal are almost unbreakable.
Solid, nonadjustable wrenches with open parallel jaws on one or both ends are known as open-end wrenches. These wrneches may have their jaws parallel to the handle or at an angle up to 90°;
most are set at an angle of 15°. Basically, the wrenches are designed to fit a nut, bolthead, or other object which makes it possible to exert a turning action.
Box-end wrenches are popular tools because of their usefulness in close quarters. They are called box wrenches since they box, or completely surround, the nut or bolthead. Practically all box-end wrenches are made with 12 points so they can be used in places having as little as 15° swing. In figure 12-4, point A on the illustrated double broached hexagon wrench is nearer the center line of the head and the wrench handle than point B, and also the center line of nut C. If the wrench is inverted and installed on nut C, point A will be centered over side "Y" instead of side "X". The center line of the handle will now be in the dotted line position. It is by reversing (turning the wrench over) the position of the wrench that a 15° arc may be made with the wrench handle.
Although box-end wrenches are ideal to break loose tight nuts or pull tight nuts tighter, time is lost turning the nut off the bolt once the nut is broken loose. Only when there is sufficient clearance to rotate the wrench in a complete circle can this tedious process be avoided.
After a tight nut is broken loose, it can be completely backed off or unscrewed more quickly with an open-end than with a box-end wrench. In this case, a combination wrench is needed, which has a box-end on one end and an open-end wrench of FIGURE 12-4. Box-end wrench use.
the same size on the other. Both the box-end and combination wrenches are shown in figure 12-5.
A socket wrench is made of two parts: (1) The socket, which is placed over the top of a nut or bolthead, and (2) a handle, which is attached to the socket. Many types of handles, extensions, and attachments are available to make it possible to use socket wrenches in almost any location or position. Sockets are made with either fixed or detachable handles. Socket wrenches with fixed handles are usually furnished as an accessory to a machine. They have either a four-, six- or twelvesided recess to fit a nut or bolthead that needs regular adjustment.
Sockets with detachable handles usually come in sets and fit several types of handles, such as the T, ratchet, screwdriver grip, and speed handle. Socket wrench handles have a square lug on one end that fits into a square recess in the socket head. The two parts are held together by a light spring-loaded poppet. Two types of sockets, a set of handles, and an extension bar are shown in figure 12-6.
Box-end The adjustable wrench is a handy utility tool which has smooth jaws and is designed as an openend wrench. One jaw is fixed, but the other may be moved by a thumbscrew or spiral screwworm Open-end adjustment in the handle. The width of the jaws may be varied from 0 to ½ inch or more. The angle of the opening to the handle is 22½° on an adjustable wrench. One adjustable wrench does the work of several open-end wrenches. Although versatile, they are not intended to replace the standard open-end, box-end, or socket wrenches.
When using any adjustable wrench, always exert the pull on the side of the handle attached to the fixed jaw of the wrench.
Special Wrenches The category of special wrenches includes the spanner, torque, and allen wrenches. The hook spanner is for a round nut with a series of notches cut in the outer edge. This wrench has a curved arm with a hook on the end which fits into one of the notches on the nut. The hook is placed in one of these notches with the handle pointing in the direction the nut is to be turned.
Some hook spanner wrenches are adjustable and will fit nuts of various diameters. U-shaped hook spanners have two lugs on the face of the wrench to fit notches cut in the face of the nut or screw plug. End spanners resemble a socket wrench but Box-end wrench have a series of lugs that fit into corresponding notches in a nut or plug. Pin spanners have a pin in place of a lug, and the pin fits into a round hole in the edge of a nut. Face pin spanners are similar to the U-shaped hook spanners except that they have pins instead of lugs.
Combination wrench There are times when definite pressure must be FIGURE 12-5. Box end and combination wrenches. applied to a nut or bolt. In such cases a torque Speed handle Ratchet handle Hinge handle Socket and Socket universal joint combined Extension bar FIGURE 12-6. Socket wrench set.
wrench must be used. The torque wrench is a precision tool consisting of a torque-indicating handle and appropriate adapter or attachments.
It measures the amount of turning or twisting force applied to a nut, bolt, or screw.
The three most commonly used torque wrenches are the deflecting beam, dial-indicating, and micrometer-setting types. When using the deflecting beam and the dial-indicating torque wrenches, the torque is read visually on a dial or scale mounted on the handle of the wrench. The micrometer-setting torque wrench is preset to the desired torque. When this torque is reached, a sharp impulse or breakaway is noticed by the operator.
Before each use, the torque wrench should be visually inspected for damage. If a bent pointer, cracked or broken glass (dial type), or signs of rough handling are found, the wrench must be tested. Torque wrenches must be tested at periodic intervals to ensure accuracy.
Most headless setscrews are the allen type and must be installed and removed with an allen wrench. Allen wrenches are six-sided bars in the shape of an I. They range in size from 64 to 2 inch and fit into a hexagonal recess in the setscrew.
METAL CUTTING TOOLS Hand Snips There are several kinds of hand snips, each of which serves a different purpose. Straight, curved, hawksbill, and aviation snips are in common use (figure 12-7). 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.
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 one-thirty-second inch from the layout line and finished by hand-filing down to the line.
Straight hand snips Circle snips Hawks-bill snips Trojan snips Aviation snips FIGURE 12-7. Snips.
Hacksaws The common hacksaw has a blade, a frame, and a handle. The handle can be obtained in two styles, pistol grip and straight (figure 12-8).
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 FIGURE 12-8. Hacksaws.
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 a 32-teeth-per-inch blade for cutting thin-walled tubing and sheet metal.
When using a hacksaw, observe the following procedures:
speed not more than 40 to 50 strokes per minute.
8. After completing the cut, remove chips from the blade, loosen tension on the blade, and return the hacksaw to its proper place.
Chisels A chisel is a hard steel cutting tool which 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 12-9).
60°-70°
1. Select an appropriate saw blade for the job.
2. Assemble the blade in the frame so that Flat cold the cutting edge of the teeth points away chisel Convex from the handle.
3. Adjust tension of the blade in the frame to prevent the saw from buckling and drifting.
4. Clamp the work in the vise in such a way that will provide as much bearing surface Single bevel as possible and will engage the greatest point number of teeth.
5. Indicate the starting point by nicking the surface with the edge of a file to break any sharp corner that might strip the teeth. Double This mark will also aid in starting the saw bevel point at the proper place.
6. Hold the saw at an angle that will keep 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, Round nose relieve the pressure and draw the blade back. (The cut is made on the forward stroke.)
7. After the first few strokes, make each stroke as long as the hacksaw frame will Diamond allow. This will prevent the blade from point 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 FIGURE 12-9. Chisels.
The size of a flat cold chisel is determined by the width of the cutting edge. Lengths will 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 which have fillets should be cut with a roundnose chisel. This chisel is also used to recenter a drill which has moved away from its intended center.
The diamond point chisel is tapered square at the cutting end, then ground at an angle to provide the sharp diamond point. It is used for cutting B-grooves and inside sharp angles.
Files 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, file holes and slots, and smooth rough edges.
Files have three distinguishing features: (1) Their length, measured exclusive of the tang (figure 12-10); (2) their kind or name, which has reference to the relative coarseness of the teeth;
and (3) their cut.
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 which 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 and not so deep as the overcut.
Files-Care and Use Files and rasps are cataloged 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, or 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 (see figure 12-11) Hand files. These are parallel in width and tapered in thickness. They have one safe edge (smooth edge) which 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.
Tang - Length Heel Face Edge Point FIGURE 12-10. Hand file.
Flat files. 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.
Mill files. 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 drawfiling and to some extent for filing soft metals.
Square files. 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.
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.
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, Half-round files. These files cut on both the fat and round sides. They may be single- or double-cut. Their shape permits them to be used where other files would be unsatisfactory.
Lead float files. These are especially designed for use on soft metals. They are single-cut and are made in various lengths.
Warding file-Rectangular in section and tapers to narrow point as to width. Used for narrow space filing where other files cannot be used.
Knife file-Knife-blade section. Used by tool and die makers on work having acute angles.
Wood file-Same section as flat and half round files. Has coarser teeth and is especially adaptable for use on wood.
Vixen (Curved tooth files)-Curved tooth files are especially designed for rapid filing and smooth finish on soft metals and wood. The regular cut is adapted for tough work on cast iron, soft steel, copper, brass, aluminum, wood, slate, marble, fibre, rubber, etc. The fine cut gives excellent results on steel, cast iron, phosphor bronze, white brass, and all hard metals. The smooth cut is used where the amount of material to be removed is very slight, but where a superior finish is desired.
Hand-taper width, parallel thickness.
Mill-taper width, parallel thickness.
Pillar-taper thickness, parallel width.
Wurding-much taper width, parallel thickness.
Square, round and three square-taper.
Half round-taper.
Knife-taper.
Vixen-parallel edges and sides.
FIGURE 12-11. Types of files.
The following methods are recommended for using files:
I. Crossfiling. Before attempting to use a file, place a handle on the tang of the file. This is essential for proper guiding and safe use. In moving the file endwise across the work (commonly known as crossfiling), grasp the handle so that its end fits into and against the fleshy part of the palm with the thumb lying along the top of the handle in a lengthwise direction. Grasp the end of the file between the thumb and first two fingers. To prevent undue wear, relieve the pressure during the return stroke.
2. Drawfiling. A file is sometimes used by grasping it at each end, crosswise to the work, then moving it lengthwise with the work. When done properly, work may be finished somewhat finer than when crossfiling with the same file. In drawfiling, the teeth of the file produce a shearing effect. To accomplish this shearing effect, the angle at which the file is held with respect to its line of movement varies with different files, depending on the angle at which the teeth are cut. Pressure should be relieved during the backstroke.
3. Rounding Corners. The method used in filing a rounded surface depends upon its width and the radius of the rounded surface. If the surface is narrow or only a portion of a surface is to be rounded, start the forward stroke of the file with the point of the file inclinded downward at approximately a 45° angle. Using a rocking chair motion, finish the stroke with the heel of the file near the curved surface. This method allows use of the full length of the file.
4. Removing Burred or Slivered Edges. Practically every cutting operation on sheet metal produces burrs or slivers. These must be removed to avoid personal injury and to prevent scratching and marring of parts to be assembled. Burrs and slivers will prevent parts from fitting properly and should always be removed from the work as a matter of habit.
Lathe filing requires that the file be held against the work revolving in the lathe. The file should not be held rigid or stationary but should be stroked constantly with a slight gliding or lateral motion along the work. A standard mill file may be used for this operation, but the long angle lathe file provides a much cleaner shearing and self-clearing action. Use a file with "safe" edges to protect work with shoulders from being marred.