aviation hand tools for cutting, drilling, machining

Note: If you are looking for the band saw page, find it here.

BASIC CUTTING TOOLS HACKSAWS The aircraft structures mechanic may be called upon to use a hacksaw to cut mild steel, metal tubing, plasticsor sheet metal. The hacksaw consists of a metal frame, handle and saw blade. The adjustable type hacksaw (Figure 2-1)accommodates different sizes of blades, from 8" to 16" in length. The non-adjustable type holds only the onesize of blade it was made for. A good hacksaw has a protective handle in case the blade breaks or your handslips while you are using the saw.

Figure 2-1 Adjustable Hacksaw

Hacksaw BladesHacksaw blades are made of hard, tempered steel. The blade may be “all-hard” or flexible. The flexible bladehas had only the teeth of the blade hardened, while the all-hard blade has been tempered throughout. Sincehacksaw blades have been tempered, they are too hard to be re-sharpened. Once a blade becomes dull, it mustbe discarded. The pitch (number of teeth per inch) may be 14, 18, 24 or 32. The part number stamped on each blade is acode number indicating the blade length and number of teeth per inch (Figure 2-2). For example, Code number1018 identifies a blade 10" long, with 18 teeth per inch, while code number 1032 identifies a 10" blade with 32teeth per inch.

Figure 2-2 Code Number

Note: Be sure the hacksaw blade is placed on the pins with the arrow on the blade pointing forward, awayfrom the handle. If the arrow is not visible, ensure that the teeth of the blade face forward as all cuttingis done on the forward stroke.

There is no such thing as an all-purpose hacksaw blade. The right blade must be chosen for the specific job. A good rule of thumb to remember in choosing the right blade is to be sure that at least two teeth of the bladeare in contact with the material being cut at all times (Figure 2-3). Soft materials such as aluminum, brass, softsteel and copper should take a 14-pitch blade. Hard materials like drill rod, and thin materials like sheet

Aviation hand tools for cutting, drilling, machining http://www.mlevel3.com/BCIT/Basic Cutting Tools.htm

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aluminum or thin wall tubing, should take a 32-pitch saw blade. To avoid ruining a hacksaw blade, always test the material to be cut first by taking the edge of a file andrunning it along the area you are going to cut. If the material cannot be filed, it cannot be cut with a hacksaw. The teeth of a hacksaw blade are alternately set in opposite directions from the sides of the blade, similar to theteeth of a carpenter's saw (see bottom of Figure 2-3). This angle is necessary so that the slot cut by the teethwill be slightly wider than the blade, thus providing the clearance necessary to prevent the blade from binding. As the blade wears and the points of the teeth become dull, they straighten slightly and the cut made by theblade becomes narrower. A dull blade has a tendency to stick in the material being cut and breaks easily.

Figure 2-3

A new blade should be started carefully in a cut that has been partially completed with a dull blade, to avoidjamming and breaking the teeth and/or blade.Using a Hacksaw1. Be sure the material to be cut is held securely in a vise or C-clamp (Figure 2-4). Secure the workpiece low

in the vise. If the material shifts while you are attempting a cut, the blade may break or the material will bedamaged. Be sure, too, that the blade is held tightly in the hacksaw frame to prevent any wandering of theblade during the cutting stroke. A notch put in the work edge with a sharp file corner may be useful foraccurate starting (maintain the two teeth in contact rule).

Figure 2-4 Using a Hacksaw

2. Never start a cut with a piece of material held at a sharp angle. This will break or dull the blade teeth, and

also violate the rule of thumb mentioned earlier about at least two teeth contacting the material to be cut at


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all times. Figure 2-5 shows the correct starting angle.

CORRECT STARTING ANGLE INCORRECT STARTING ANGLE

Figure 2-53. Grasp the hacksaw securely, one hand on the grip or handle and one hand on the frame. In starting the cut,

guide the blade with the thumb of your other hand (Figure 2-5) until the cutting slot is established. Like afile, a hacksaw cuts only on the forward stroke.

4. Use a little downward pressure on the forward stroke, but lift the saw slightly on the return stroke so that

the teeth scarcely touch the material being cut. 5. The stroke should be long and steady so that practically all the teeth on the blade are used. Lighter

pressure should be used on soft metals and thin materials than is used on hard metals and heaviermaterials. Insufficient pressure on the forward stroke will dull the teeth by rubbing them against the metalwithout cutting it.

6. Be sure to keep the saw blade moving in a straight line by keeping your shoulder, elbow and forearm in line

with the saw. The straight line is important to avoid any twisting or wobbling of the blade. 7. Do not rush when using a hacksaw. Most beginners saw too rapidly. Approximately 60 forward strokes

per minute is maximum. A good mechanic uses approximately 40 to 50 forward strokes per minute, witheven pressure.

By following correct hacksawing procedures you will use less effort, your cuts will be made faster, and theblades will last longer.

FILES Of all metalworking hand tools, files are the most widely used. There are more than 3,000 different kinds, sizesand cuts of files available today. We will attempt to cover only the more common ones. As illustrated in Figure 2-6, each part of a file has a particular name. Become familiar with these names asthey will be referred to in the descriptions of the different kinds of files and their characteristics.

Figure 2-6 Parts of the File

The size of the file is not measured in total length; the tang is not included. The size is determined by thelength from the point to the heel only. Teeth are cut into the faces, and sometimes the edges, of the file body.


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Files have the following general uses: · to remove extra material· to fit material together more accurately· to correct errors resulting from inaccurate machining (threads of screws and bolts, etc.)· to file a flat or smooth surface· to file an edge, such as on sheet metal· to file a notch, slot or square or round hole. Types of FilesThere are different kinds of files to give the best results with different types of metal. All files are classified in two ways, by shape and by cutting face. ShapesThe three most popular shapes of files are the flat file, the round file and the triangular, or more correctly, thethree-square or three-cornered file. In Figure 2-7, notice how the flat file tapers at the point. Generally, the flat file has teeth on both edges. Flatfiles are used for general-purpose filing. The round file, also known as the rat-tail file (Figure 2-7), is tapered throughout its length, with teeth coveringthe full circumference. This file is used primarily for enlarging circular openings or filing curved surfaces.

Figure 2-7 File Types

The three-square file, also known as the three-cornered file (Figure 2-7), is used to clean out corners of asquare shape or to file at odd angles. The file is tapered its full length to the point. All faces have teeth, andthe corners between the faces are left sharp. Cutting FacesThe types of cutting faces can again be divided into two different classifications. First of all, they are classedas either single cut or double cut (Figure 2-8), which refers to the actual design of the cutting edges on the fileface. The single-cut file has one unbroken course of teeth running across the face of the file. The double-cut file hastwo broken courses of teeth crossing each other. Curved tooth, “vixen” or “body files” are used for smoothing soft materials such as aluminum, plastics or autobody filler.


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For both single and double cut files, the second classification identifies the grade of the file teeth. There are sixdifferent grades of file in either the single or double cut:

Figure 2-8

· rough cut · second cut· coarse cut · smooth cut· bastard cut · dead-smooth cut

The only difference among the grades is the spacing between the teeth. Naturally, the rough-cut file has thegreatest space between the teeth. As the cut becomes smoother, the spacing decreases. Remember, though,the spacing is in relation to the overall size of the file. For example, a large bastard-cut file has more spacebetween the teeth and larger teeth than a small bastard-cut file has, even though both are bastard-cut files. The single-cut file is used when a smooth finish is desired. The double-cut file is used for rough, fast metalcutting or where large amounts of material must be filed off.File HandlesFiles are sold without handles, so the first step in using a file is to fit it with the proper handle. Always select ahandle to properly fit the file - neither too large nor too small for the file tang. Note: There are two excellent reasons for using a file handle on all files. The first and most important is your

safety. The tang of a file is usually pointed. If you meet an obstruction while filing and the file stopssuddenly, your hand could be severely punctured (Figure 2-9). Secondly, the handle helps guide thefile and the work can be done more accurately and more quickly if a good file handle with a strongferrule, or metal collar, is used (Figure 2-10).

Figure 9 Figure 10 File Handles How to Use Files


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If you are new to working with files, the best advice is for you to take your time, check your work frequentlyand do the job correctly. Some very commonly made mistakes are: · rocking the file from left to right as the material is being filed, creating a curved, rather than a flat surface.

· bearing down too hard in the middle of long cuts, thereby creating a dip in the middle of the material.

· filing for too long without checking the material. You may fail to detect the removal of too much material

or incorrect filing methods.

· filing with arm movement only. Your body should lean forward slightly during the forward stroke, thenreturn to an upright position during the backward stroke.

With practice, you will soon feel the work through the file. Just by feel, you will be able to tell how muchmaterial is being removed, whether you are filing at too great an angle, coming too close to an edge or even ifthere is any unevenness in the surface of the material. Remember, a file is not a crude tool. In the hands of anexpert, it becomes almost a precision tool. Note: Your workpiece should be placed in a bench vise, and you should be sure to protect the workpiece from

the vise jaws by placing pieces of wood, plastic or soft metal between the vise jaws and the workpiece. When moving the file across any work, hold the file as shown in Figure 2-11 and move it straight ahead or atjust a slight angle. Hold the handle so that the handle end fits into the heel of your hand, with your thumb lyingalong the side of the file. Your forearm and the file should form a straight line.

Figure 2-11 Filing Technique

The point of the file is held by your thumb and first two fingers of the other hand. For heavy filing strokes, thewhole underside of your thumb should press down. On lighter strokes, your thumb can be placed more at aright angle to the file. Draw FilingDraw filing (Figure 2-12) is used when you wish to finish a smooth surface and only small amounts of materialare to be removed at a time. Only the single-cut file should be used for this purpose, never the double-cut file.


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Figure 2-12 Draw FilingHold the file in both hands with your thumbs approximately 13 mm to 38 mm (2" to 12") from each side of thematerial being cut. Then either push or pull the file straight across the surface on a forward stroke. Again, raise the file slightly on the back stroke, as with ordinary filing, except in the case of soft metals such asaluminum, brass, copper or lead. With these metals you can apply pressure on the backstroke withoutdamaging the file. In using different grades of files, the angle at which the file is moved across the material will vary slightly. Trial filing angles will provide which is best for the type of material being cut. When filing a piece of material, always stop and check your work for even cutting and squareness as you file. If you are filing incorrectly or at the wrong angle, you will discover the problem before the material has beenruined. A more accurate method of checking your work for even cutting is with a steel square (Figure 2-13). Hold thebody of the square firmly against one edge of the material and check that no clearance is visible between thebottom of the blade and the top edge of the material. If clearance is visible, your filing methods are incorrect.

Figure 2-13 Checking for Square

SHAPES OF FILESClass Trade Name Grade Shape of Cross Section


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Single Cut Mill File (Saw File)

CourseBastard

Double Cut Machinist Second CutSmooth

CurvedTooth

Metalworker StandardFineSmooth

Figure 2-14

Another method for checking the file accuracy of a flat surface is a method known as crossing the stroke. Theangle of the normal filing stroke Figure 2-14 (A) is changed to approximately 45° Figure 2-14 (B). Changingthe filing angle from the previous stroke immediately shows the presence of any high spots by file markvariations and new shiny areas on the surface of the material. Cleaning FilesBefore starting any filing operation, especially the filing of mild steel or soft non-ferrous metals, the file shouldbe coated with chalk. The chalk prevents metal cuttings from becoming pinned or trapped in the teeth of thefile. Metal particles trapped in the teeth of a file not only reduce the file's ability to remove metal from theworkpiece, but may also cause damage to the surface of the workpiece.As soon as you notice a build-up of particles on your file, brush them off with a file card. A file card (Figure2-15) has wire bristles on one side and fiber bristles on the other.

Figure 2-15 File Card

Begin cleaning the file with the fiber bristles. Then, if necessary, remove any particles still left in the teeth withthe wire bristles. Sometimes after filing soft metals such as aluminum copper and lead, filings will remain stuck between theteeth even after using the file card. If this happens, you should use a sharp, pointed piece of hard wood of soft


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iron to pick the remaining filings from between the teeth. Note: Never use a piece of hardened steel (such as a pointed punch or chisel) to pick file teeth clean.

Damage to the teeth can result. Storing FilesMore files wear out from abuse than from use. When not in use, files should be kept separated from each otherand from other tools to prevent damage to the file teeth. A simple method for safely carrying your files in a tool box (or any place for that matter) is to fold a piece ofcardboard into an accordion shape (Figure 2-16). Each fold should be just wide enough to entirely cover thefile blade. Place a file in each fold of the cardboard and fold the accordion together. Using a strip of old innertube, cut approximately 13 mm (2") wide, secure the folds of cardboard.

Figure 2-16 File Compartments

Once your files have been securely wrapped, always store them in a dry place. Rust will adversely affect thecutting edge of the file teeth.

Figure 2-17

Files Available in Stores

4" flat smooth4" flat bastard4" round smooth

4" mill bastard4" warding smooth4" warding 2nd cut


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4" round 2nd cut4" round bastard

4" warding bastard

6" flat smooth6" flat bastard6" warding smooth6" warding 2nd cut6" warding bastard6" mill bastard6" hand smooth6" knife smooth6" cantsaw

6" half round smooth6" half round bastard6" round smooth6" round 2nd cut6" round bastard6" square smooth6" square bastard6" slim taper6" double extra slim taper

Files Available in Stores

8" flat smooth8" flat bastard8" mill bastard8" hand smooth8" hand 2nd cut8" hand bastard8" half round smooth8" half round 2nd cut8" half round bastard8" cantsaw

8" round smooth8" round 2nd cut8" round bastard8" square smooth8" square bastard8" slim taper8" extra slim taper8" double extra slim taper8" half round rasp8" woodcraft rasp

10" flat smooth10" flat 2nd cut10" flat bastard10" mill 2nd cut10" round bastard

10" half round smooth10" half round 2nd cut10" half round bastard10" square smooth10" square bastard

12" flat smooth12" flat 2nd cut12" flat bastard12" mill smooth12" mill 2nd cut12" mill bastard12" square smooth12" square bastard

12" half round smooth12" half round 2nd cut12" half round bastard12" round smooth12" round 2nd cut12" round bastard12" aluminum

14" flat smooth14" flat bastard14" mill smooth14" mill bastard14" square bastard

14" half round smooth14" half round 2nd cut14" half round bastard14" round smooth14" round bastard

16" flat smooth

16" half round bastard

EMERY CLOTH, WET AND DRY SANDPAPER


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Mechanics use emery cloth to finish and polish metals. The emery on emery cloth is a natural abrasive, animpure form of crystalline alumina. This emery grit is bonded to either paper or cloth backing, cloth being themost widely used. It usually comes in three grades or grits: fine (100-140), medium (80-100) and coarse(60-80). The cloth backed emery can be used wet (with oil) or dry. One characteristic of emery cloth that should be remembered is that, as it wears down from use, the crystallinestructure of the emery continuously breaks away and becomes smaller so the emery becomes finer and finer asyou use it. This is an advantage, as this is the natural progression you desire when polishing or finishing a pieceof metal. Emery cloth is economical to use, as it can be re-used repeatedly.

Figure 2-18 Surface Finish

To apply a smooth finish to a metal surface, perform the following steps (Figure 2-18): · Obtain a 2-inch strip of the proper grade of abrasive.

· Wrap the strip, Figure 2-18 (A), around the center of a file, Figure 2-18 (B), holding it with your thumbs.

· Apply a small amount of cutting oil to the metal, Figure 2-18 (C), being worked. Move the file back and

forth across the metal until the finish you desire is obtained. Always start with a rougher grade of abrasive, changing to a finer and finer abrasive cloth until the material isas smooth as you wish. A smooth finish on a metal surface can also be achieved by using wet and dry sandpaper in finer and finergrits. Wrap the sandpaper around the file in the same way as you would with the emery cloth. The sandpaperis best conserved if a full sheet is folded into four and ripped into four separate pieces and used a quarter at atime. As the name “wet and dry” implies, the job may be done using the paper dry or with water. The waterhelps float the particles away, but can lead to rusting of the file and the work if left too long. For that reason, itis best to use the paper dry. Wet and dry sandpaper may also be taped in the full sheet form to a very flatsurface and the project moved against the sheet. This will help create a very flat smooth finish.DRILLING OPERATIONS There are several operations involving holes that are often done on the drill press but that can be achieved byhand processes.


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Figure 2-19 Drilling-Machine Operations

Drilling is the operation of producing a circular hole by removing solid metal. The cutting tool used is called adrill. Reaming is an operation of sizing and finishing a hole by means of a cutting tool having several cutting edges. This tool is called a reamer. Reaming serves to make the hole smoother, straighter and more accurate. Boring is the operation of enlarging a hole by means of an adjustable cutting tool with only one cutting edge. Counterboring is the operation of enlarging the end of a hole cylindrically, as for a recess for a fillister-headscrew. Countersinking is the operation of making a cone-shaped enlargement of the end of a hole, as for a recess fora flathead screw. Spot-facing is the operation of smoothing and squaring the surface around a hole, as for the seat for a nut orthe head of a cap screw. Tapping is the operation of forming internal threads by means of a tool called a tap. To withdraw the tap bypower in a drill press requires either a reversible motor or a reversing attachment or tapping attachment. Towithdraw a tap by hand, loosen the chuck or other holding device and remove.HAND AND BREAST DRILL Although it is very unlikely that an Aircraft Structures mechanic will be required to use a hand drill or breastdrill on a regular basis, there may be an occasion when doing an aircraft repair in the Amazon jungle or in anarctic snowbank when no other means of making a hole is available. Holes can be drilled by hand or by machine. When drilling by hand, the brace, hand or breast drill can beused. The latter two are the more practical. The electric and pneumatic drills are portable and usuallyclassified as hand drills. Drilling by machine is done by power-operated drill presses. The hand drills,including the electric and pneumatic types, can be used in the shop or on the job. However, the latter needselectricity or air for power. Description of the Hand and the Breast DrillThe hand drill consists of a metal frame, gears and a chuck. The chuck holds the twist drill and is turned by acrank and gears (Figure 2-20). Most of the hand drills are single speed with a ball thrust bearing and adjustablegears to prevent play of the larger gear. The end handle is usually wood with a hollow compartment to hold thedrills. A detachable wooden side handle is provided for convenience when drilling. The capacity is from 1/64"to 3" diameter straight shank drills.


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Figure 2-20 Hand Drill

The breast drill is similar to the hand drill, but will take a larger drill. Instead of the wooden end handle, thebreast drill has an adjustable breast plate (Figure 2-21). This drill can be obtained in two speeds; the low speedis used for the larger drills and the high speed for the smaller drills. The capacity varies from 1/64" to 2"diameter straight shank drills.

Figure 2-21 Breast Drill

The chuck contains jaws which hold the twist drills. These jaws are contracted or expanded by turning thesleeve (Figure 2-22).

Figure 2-22 Chuck

DRILLS Parts of a Twist DrillThe twist drill is the most common type of drill in the aircraft industry.

Made of hardened Tool Steel, the twist drill is designed to produce around hole in materials sometimes as hard as the drill itself. A drill consists of the following parts (Figure 2-23):

· Margin (A), the cutting edge around the body· Flutes (B)· Shank (F)· Body (G)· Heel (I)· Dead center (H)· Axis (E), the centerline of the drill· Lip (D), the cutting edge· Body clearance (C)· Web (J), width of dead center


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Figure 2-23 A drill and its parts function as follows: The lips, Figure 2-23 (D), are the parts of the drill which perform the cutting. The flutes, Figure 2-23 (B), help to form the proper cutting angle to the lip, Figure 2-23 (D), and permit the drillto cut freely. They cause the chip to curl tightly within itself and spiral out of the hole. The flute, Figure 2-23(B), allows cutting lubricant to flow to the cutting lips. The second angle that forms the cutting edge on the lip, Figure 2-23 (D), is the heel, Figure 2-23 (I). For themost part, this is the only surface that is reground when a drill becomes dull and will not cut. Body clearance, Figure 2-23 (C), is smaller in diameter than the margin, Figure 2-23 (A). This is to reducefriction between the drill and the walls of the hole. However, the margin, Figure 2-23 (A), is the full diameterof the drill and extends the full length of the flute, Figure 2-23 (B). The dead center, Figure 2-23 (H), is the sharp edge at the extreme tip of the drill. It is formed by theintersection of the two cone-shaped surfaces of the point and should always run true to the axis, Figure 2-23(E), of the drill. Damage to the shank, Figure 2-23 (F), the part of the drill that is held in a drill chuck, is the most commoncause of drill failure. If such damage occurs, the drill will not run concentric (true) about its axis, Figure 2-23(E). Note: Be sure that the shank, Figure 2-23 (F), is free of burrs (rough edges) that might cause the drill to runout (wobble). Types of Common DrillsInexpensive drills are made of Carbon Steel. The more expensive drills, especially those designed to cut thetougher metals, are made of high-speed alloy (two or more metals) steel. The latter last longer and thereforeare most widely used.

Figure 2-24

The twist of the flutes, Figure 2-24 (A), and the thickness of the web, Figure 2-23 (J), determine the type ofwork for which the drill is best suited.


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Drill Figure 2-24 (B) is an all-purpose drill. It can be used on most materials, such as cast iron, steel, steelforgoings, sheet metals, plastics, aluminum and wood. Drill Figure 2-24 (D) has “fast” spiral flutes, Figure 2-24 (E). That is, there are more twists per inch than areused on a general-purpose drill Figure 2-24 (B). This drill is used on thick aluminum sections die-cast metal,copper, slate, etc. On such metals as mentioned earlier, it helps if the drill flutes are polished, along with the fast spiral flutes. The drill can then eject chips quickly and easily. Drill Figure 2-24 (F), however, has a longer twist to its flutes, Figure 2-24 (G). This type of drill is used onsuch materials as Bakelite, hard brass, fiber, hard rubber and various molded plastics. Drill Figure 2-24 (H) is suitable for heavy-duty drilling in tough metals. The flutes, Figure 2-24 (I), on this typeof drill have more twists per inch than that of the general-purpose drill, Figure 2-24 (B), and not quite as manytwists as that of drill Figure 2-24 (D). They also have a heavier web that enables them to withstand theincreased strains produced in drilling heat-treated alloy steel forgoings. Drill Figure 2-24 (J) is especially useful in the automotive industry on sheet metals; using air or hand drills. This drill is of heavier construction than a general-purpose drill and has a smooth finish that prevents thematerial from binding or building up on the drill when in use. The toughest of all drills, Figure 2-24 (K), is designed for drilling types of stainless steel and iron that aredifficult to machine. It has a shorter overall length than the common drill, Figure 2-24 (B), and a thicker web,Figure 2-24 (C), enabling this drill to withstand the pressures involved in drilling tough metals. Special Drills

Figure 2-25 Multi-Groove Drill (Core Drills)The drills in this section have special features designed to perform special tasks in a more efficient manner. Drill Figure 2-25 (C) has three flutes, Figure 2-25 (B), a shallow angle and a flat point, Figure 2-25 (A). DrillFigure 2-25 (E) has all the same features as drill Figure 2-25 (C), except that drill Figure 2-25 (E) has fourflutes, Figure 2-25 (D). Both of these drills are used to follow a hole already made by a smaller drill (pilothole), thereby enlarging cored holes (these are holes that already exist in castings). Straight-Flute Drills

Figure 2-26 Drill Figure 2-26 (B) has straight flutes, Figure 2-26 (A), which are designed to work in soft materials like brassand soft cast alloys. They are also suitable for use on thin sheet materials. This drill will not “grab” thematerial as it breaks through the surface, thus producing a true hole with little risk of breaking the drill.


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Extension Drills

Figure 2-27

Extension drills, Figure 2-27 (C), are available in different lengths, Figure 2-27 (A); 12 inches is the mostcommon. The flutes, Figure 2-27 (B), of a 12-inch extension drill will occupy only about 2 inches of the drill'stotal length. The remaining stock is devoted to the shank, Figure 2-27 (C). Extension drills are used for drillingholes in places which cannot be reached by the standard drill, Figure 2-27 (D), of ordinary length. This drill should not be used unless absolutely necessary. Use a drill guard (an aluminum tube slipped over thedrill) to protect adjacent structure from drill whip, and to make it possible to guide the drill by hand. Hold thedrill guard as near the drill point as possible. Note: Use of drills over 3 inches long is not safe at speeds over 6,000 rpm.

Figure 2-28

Skin Drills

Figure 2-29

A skin drill may be used in manufacturing, Figure 2-29 (B), has flutes, Figure 2-29 (A), extending over most ofits length and has a very short shank, Figure 2-29 (C). This drill is much shorter than the common drill. Theadvantage of the skin drill is that it can be sharpened a great many times; thousands of holes can be drilledbefore discarding it. The purpose and design of the skin drill is for production drilling a great many holes inquick succession in aircraft skin, auto bodies and situations where sheet stock is used extensively. Split Point Drill


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Figure 29a

Split point drills are specially designed for use in the aircraft sheetmetal industry. The background pointreduces the size of the dead center and improves the starting accuracy of the drill when free-hand drilling. With care, a sharp split point drill can be started accurately without the use of a center punch. Determining Drill Size

Figure 2-30

The decimal equivalent table, Figure 2-30 (A), shows how drill sizes are expressed. They are expressed innumber, letter and fractional size of drills as well as metric. Starting at the upper left corner of this table atcolumn, Figure 2-30 (B), reading down in each of the columns and moving to the right, you will find the drillsnumbered from 80 to 1 inclusively. The number 80 drill is the smallest size given, having a diameter of.0135-inch as indicated in column (C) Figure 2-30. The number 1 drill is the largest of the number series andhas a diameter of .2280-inch. At intervals in the numbered series, you will find certain drill sizes expressed in fractions of an inch, such as1/64-inch, 1/32-inch, 3/64-inch, etc. Notice that the fractional drills increase in size by steps of 1/64-inch; inother words, a 1/32-inch drill is 1/64 inch larger than a 1/64-inch drill, a 3/64-inch drill is 1/64-inch larger thana 1/32-inch drill and so on throughout the table.


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Directly under drill No. 1 in column (D) of Figure 2-30, you will find the letter “A” used to designate anotherseries of drills; the actual diameter of drill “A” is given in column (E) of Figure 2-30, shown here as .2340. It islettered instead of numbered, ranging from size “A” at .2340-inch to size “Z” at .4130-inch, Figure 2-30 (F). Throughout the balance of this table, the drill sizes are arranged according to their actual diameters and areexpressed in fractions of an inch. That is, starting with a 27/64-inch drill directly under “Z”, Figure 2-30 (F),each succeeding drill size is 1/64-inch larger in diameter than the one preceding it. The table ends with a drillof 1.00-inch diameter. However, the diameters of all drills larger than 1 inch are also expressed in inches andfractions of an inch and increase in steps of 1/64-inch. Example: The next size over 1 inch would be 11/64-inches, then 11/32-inches and 13/64-inches.

Figure 2-31

The decimal table (Figure 2-30) not only gives the drill sizes but also supplies the exact diameter of each drill,expressed in decimals of an inch. The size, Figure 2-31 (A), of most drills listed in the table is stamped on theshank, Figure 2-31 (B), either as a letter or as a fraction of an inch. Drill Size Gauges

Figure 2-32

Drill size gauge, Figure 2-32 (A), is made to fit all the drills that exist in a NUMBER set (from 80 to 1). Drill size gauge, Figure 2-32 (D), is designed to fit all LETTER-size drills. There is also a gauge made to fitFRACTIONAL drills. No. 80 is the smallest size drill that exists in the three drill sets mentioned. This drill has a diameter of.0135-inch. As you can see, it is not possible to stamp the number 80 on this drill, hence the drill gauge.The drill gauge, Figure 2-32 (A), is one way of differentiating one size of drill from another. In order to do this,pass the drill, Figure 2-32 (B), into a hole, Figure 2-32 (C), of the gauge until the drill fits snugly. At this point,the size given on the drill gauge is the size of the drill being tested. Drill SetsSo that no time will be lost in selecting a drill of the size required for a certain job, drill set, Figure 2-33 (B), isused. The drill set shown in Figure 2-33 holds drills from 1 to 60. The shank, Figure 2-33 (A), of each drill fitssnugly in its proper hole. Each hole is marked with its size.


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Figure 2-33

How to Sharpen DrillsThe importance of correctly grinding twist drills cannot be too strongly emphasized. A drill, no matter howwell designed or heat-treated, will fail in its performance if the point is not ground properly. The greatestpercentage of failures experienced in drilling are caused by hand sharpening and incorrect repointing. Drillssmaller than ¼” in diameter should not be sharpened by hand for this reason. For best results, a drill should be reground or repointed at the first sign of dullness along the cutting lip Figure2-34 (A). Failure to do so may cause the drill to break due to the increased load imposed on the cutting edgesby the dullness.

Figure 2-34

Note: If a drill is allowed to become too dull before repointing, it will be necessary to grind off a considerable

amount of material before a new and correct point can be obtained, which is obviously wasteful. When grinding a drill, the following three factors must be considered: 1. Lip clearance angle, Figure 2-35 (B).2. Length of the lips, Figure 2-35 (C).3. Location of the point or dead center, Figure 2-35 (D), in relation to the axis, Figure 2-35 (E).


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Figure 2-35

Grinding Lip ClearanceLip clearance, Figure 2-36 (A), is the most misunderstood angle of a drill. It is the angle and face that must bereground when a drill becomes dull. A drill that has no lip clearance, Figure 2-36 (B), could not cut into a piece of steel, because the surface, Figure2-36 (C), would always be in contact with the metal. Such a drill would merely rub on the steel surfacewithout penetrating it.

Figure 2-36

Therefore, if the lip (B) on Figure 2-37 is to penetrate (if its edge is to cut), we must grind away the surface (A)on Figure 2-37 back of the lips (B) on Figure 2-37. Grinding away surface (A) on Figure 2-37 gives a drill“relief” so that the lip can penetrate the metal. Surface (A) on Figure 2-37 is referred to as the heel and should be ground away at an angle of 12°, Figure 2-37(C). In all cases, this angle of 12° is the angle at the circumference (D) on Figure 2-37, that is, the outer edgeof the drill. Looking down on the drill point, if the correct clearance of 12° is given to the lip (E) on Figure 2-37, an anglewill have been produced between the point on dead center, Figure 2-37 (F), and the lip, Figure 2-37 (E). Thisangle should be between 120° and 135°, Figure 2-37 (G).

Figure 2-37


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Note: If the angle of the lip clearance is too great, the edges of the cutting lips will break down because they

will not have sufficient material backing them to support the lip.

If not enough lip surface is ground away, the clearance of the point will be so reduced that it will ceaseto be a cutting edge and refuse to bite into the metal. This condition can result in splitting the drill upthe center.

Using Drill Point GaugesAfter the point has been properly ground so that the angle of lip clearance is correct, the point must be checkedto ensure that:

Figure 2-38

1. The two lips, Figure 2-38 (A), are the same length. 2. The angles, Figure 2-38 (B), of both lips in relation to the axis, Figure 2-38 (D), of the drill are equal at

59°. This angle is recommended for general-purpose use. 3. The angle, Figure 2-38 (E), between the dead center, Figure 2-38 (F), and the lip, Figure 2-38 (G), is

between 118°and 135°. Drill point gauges, Figure 2-38 (C) and (H), are fixed-angle gauges produced forthis purpose. However, different types are available. Some of them provide a means whereby the settingof the angle can be varied, as is sometimes done when grinding drill points for special purposes.

Note: If the drill point is not equal from one side to the other (if the 59° angle is not equal and the lips are not

the same length), the drill will produce a hole larger than the drill. Excessive wear to the drill anddamage to the material will result.

A quick way to check the correct heel angle, Figure 2-39 (A), of a drill is to use a piece of paper, Figure 2-30(B), 82 inches long and 2 inches wide. Place a mark 13 inches, Figure 2-39 (D), along one edge of the paper. Wrap the paper around the drill, keeping one edge of the paper along the heel angle. The edge, Figure 2-39(C), of the paper should line up with the mark on the paper if the heel angle is correct.


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Figure 2-39

Rake AngleRake angle, Figure 2-40 (B), is designed into a drill. As stated earlier, it is produced by the twist of the flutes,Figure 2-40 (A). However, this angle and others will change in some series in order to function better incutting some materials. Be sure to select the right drill for the cutting job.

Figure 2-40

Note: When attempting to grind anything on a bench grinder, safety glasses must be worn. To produce a drill point correctly by hand requires a lot of practice. Practice is required because two or moremovements take place at the same time. To sharpen a drill on a conventional grinder (emery wheel Figure 2-41 (A)), hold the drill, Figure 2-41 (C),against the face of the wheel so that the centerline, Figure 2-41 (E), of the drill will be at a 59° angle, Figure2-41 (G), with the face of the wheel. This will produce the correct angle on the drill lip, Figure 2-41 (B). Press the point of the drill, Figure 2-41 (C), against the wheel lightly. Be careful not to hold the drill againstthe emery wheel too long or the metal will burn. Frequently dip the drill end into water to preserve the temper(hardness) of the drill. During this procedure, use your left hand as the fulcrum and place your right hand nearthe end of the shank so that you can control the angular (up and down, Figure 2-41 (D)) position of the drill.


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Figure 2-41

While contacting the face of the wheel, move the drill slowly downward in the direction of the arrow (D) onFigure 2-41 to an angle of about 30°. At the same time rotate the drill in the direction of arrow (F) on Figure2-41. Repeat this movement for both sides of the drill until all the conditions and angles described earlier areproduced. Drill Grinding AttachmentIn shops where a great deal of drill grinding is required and a high degree of accuracy is a must, it is generallythe practice to use a precision drill grinding attachment, Figure 2-42 (A). There are many different typesavailable today. For the proper procedure in the use of the attachment, refer to the manual supplied with theattachment.


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Figure 2-42

COUNTERSINKS Hole Preparation for Flush RivetsIt is extremely important for high-speed aircraft that the skin be as smooth as possible. In order to have therivet heads fit flush with the surface, we must prepare the skin by either cutting away a portion of the metal tomatch the taper of the rivet head, or bending, or forming, the edges of the hole to fit the rivet head.

Figure 2-43 The MS20426 rivet has a head angle of 100 degrees.

The flush rivet used almost exclusively in modern aircraft is the AN426 (MS20426) rivet. It has a head angleof 100 degrees. CountersinkingIf the top sheet of the metal being joined is thicker than the tapered portion of the rivet head, the materialshould be countersunk. That is, it should be cut with a tapered cutter. The thinnest material that can becountersunk for the various rivets is given here:

Rivet Diameter Minimum Skin Thickness3/32-inch1/8-inch

5/32-inch3/16-inch

0.032-inch0.040-inch0.051-inch0.064-inch

A standard countersink can be used in a drill motor, but the difficulty in cutting the hole to the correct depthmakes this tool impractical when you have more than a few holes to countersink.

Figure 2-44


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The stop countersink or microstop countersink is used when a large number of holes must be countersunk. Acutter shaft fits into the chuck of a quarter-inch air or electric drill motor, and the cutter screws onto this shaft. Pilots are available for all of the popular rivet sizes and the shank of all of the pilots are the same. Because ofthis, one cutter will work for all size rivets; you need only replace the pilot to countersink holes of differentsizes. The body and stop fit over the cutter shaft and may be held still while the cutter is driven by the drillmotor. Adjust the countersink to cut the proper depth, by using a piece of scrap metal the thickness of the top sheetbeing riveted. Drill some holes the size used for the rivet and adjust the stop of the countersink by screwing itup or down on the body and locking it with the locknut. Hold the stop with one hand and run the countersinkinto a hole until the fiber collar touches the sheet, and then take it out. Slip the proper rivet into the hole. Itshould fit so its top is flush with the skin. When the stop is adjusted and the locknut is tightened against it, thecountersink should cut all of the holes to a uniform depth. When using it, be sure to keep the stop fromspinning and marking the metal.

Figure 2-45

METAL-CUTTING SNIPS AND SHEARS

Figure 2-46


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Figure 2-46a

Aviation snips, Figure 2-46, as they are known, are used for cutting aircraft aluminum sheet alloys. They willalso cut stainless steel and mild steel sheet in the .050 range. The compound leverage action makes them easyto use. They are also used for cutting sheet brass, copper, etc. The right- and left-cutting snips are useful forcutting curves and circles in metal. Aviation snips should not be used for cutting wire or rod as damage to thecutting edge will result. For cutting aluminum sheet and light sheet steel, gasket material and rubber, the straight snip or duckbill snip,Figure 2-46a, is recommended. Like the aviation snips, the straight snip, cuts in a straight line, and the duckbillsnip, cuts in a curve (in either direction). When cutting sheet metal with snips, it is often advisable to cut away the scrap in one or two small cuts. Thiswill leave less distortion in the part you are making. DEBURRING TOOLS Deburring tools are used to remove burrs or rough edges from material, parts, drilled holes, etc. Burr QwikThe Burr Qwik (Figure 2-47) is used for deburring holes.

Figure 2-47

Edge Breaker (ST 907)The edge breaker (ST 907) (Figure 2-48) is used for removing burrs from sheet material edges.

Figure 2-48

Machinist's Triangular BladeThe machinist's triangular blade is a general-purpose deburring tool (Figure 2-49). Do not use it for deburringholes.


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Figure 2-49

Chip ChaserThe chip chaser (Figure 2-50) is inserted edgewise between sheets in a stackup to remove burrs in holes nearthe sheet edge and to remove chips. It must be used with care to avoid scratching skins; apply skin tape asneeded.

Figure 2-50

WHITNEY PUNCH This hand punch (Figure 2-51) is sometimes used in assembly areas for pickup work. The tool is issued as a kitthat contains interchangeable punches and dies ranging from 0.094 (3/32) inch to 0.281 (9/32) inch in diameter,in 0.031 (1/32) inch gradations.

Figure 2-51

The punch is changed by removing the intermediate screw and sliding the intermediate arm forward, thusdisengaging the slotted shank of the punch. The die is mounted in a threaded hole through the lower jaw, anarrangement that provides both easy interchangeability and quick adjustability. A throat-depth gauge with alocking screw is mounted on the side of the frame. Approximate punch capacity in 7075BT6 aluminum alloy is 0.281 (9/32) inch-diameter holes in material up to0.048 inch thick and 0.188 (3/16) inch-diameter holes in material up to 0.075 inch thick. Punch capacities inother alloys may be estimated from this. It should be noted that Whitney punch holes are acceptable as pilot holes only. Holes must then be drilled orreamed to size. As a general rule, punched holes must be increased by at least 0.031 (1/32) inch by drillingand/or reaming. This is necessary to remove the probability of cracks developing from the punched holes. CHASSIS PUNCHES The chassis punch, once used only for installing radios and other avionics appliances, has become a useful tool


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for the sheet metal mechanic because of its ability to make neat holes. Chassis punches are used to makelightening holes in newly formed ribs or access holes for inspection purposes. Drill a hole to accept the drive bolt. Run the drive bolt through the die, through the hole in the metal andthread it into the cutter. Turn the drive bolt with the correct size wrench, and the cutter will shear a holethrough the material.

Figure 52 RIVET CUTTER A rivet cutter (Figure 2-53) is used to cut rivets to the proper length for a particular installation. The cutter ishand-operated, has sized holes so that the rivets are not distorted when cut, and has a gauge which can be setto the desired length of the cut rivet.

Figure 2-53 Rivet Cutter

SOLID-JOINT DIAGONAL CUTTING PLIERS As the name implies, diagonal cutting pliers, Figure 2-54, are pliers made with a diagonally cut head or face,(A), and a hard steel cutting edge to cut wire or other metal objects close to the surface.


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Figure 2-54 Solid-Joint Diagonal Cutting Pliers

Figure 2-55

With the back of the cutter tip ground flatter, Figure 2-55 (A), diagonal cutters make useful rivet cutters, whena small number of rivets must be shortened. Once the back is ground flat, however, the cutting edge is nolonger strong enough to cut wire and must be used only for cutting rivets. HAND NIBBLING TOOL A hand nibbling tool (Figure 2-56) is used to remove metal from small areas by cutting out small pieces ofmetal with each “nibble”. This tool is most useful in confirmed areas where using snips is not possible andwhere a minimum amount of metal distortion is desired.

Figure 2-56 Hand Nibbling Tool TAPS AND DIES


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Figure 2-57 The tap and die are tools for cutting internal and external threads. The tap cuts threads for a screw or bolt bycutting threads in a hole drilled in some material (usually metal). The die cuts threads on a rod or bolt to accepta nut. The tap is a formed tool used for the cutting of internal threads. Taps are available in both hand and machinetypes. Hand taps, however, may also be used in machines and operated under power. Practically the onlydifference between most hand and machine-operated taps is the type of shank. The hand tap has a square end. Taps are highly tempered for strength, thus making them very brittle. If you break a tap off in a hole, it is verydifficult to remove, so use them carefully. Taps are made from two types of steel, carbon steel and high-speed steel. Carbon steel is simply purified ironto which carbon has been added to produce hardness. Carbon steel taps are less expensive than high-speedsteel, will not cut some materials and will not last as long for general use. High-speed steel is a combination of iron, carbon, tungsten, chromium, vanadium, manganese, molybdenumand sometimes cobalt. These elements provide the steel with the properties of hardness and toughness and theability to withstand high cutting temperatures and resist wear. High-speed steel taps will operate attemperatures up to 1100°F without the cutting edges breaking down. This is approximately 700°F more heatthan the carbon steel tool will stand. The tap threads most commonly used in the aircraft industry are the National Coarse (NC) and National Fine(NF) threads, but you should be aware of two other types of threads. They are the National Pipe Thread (NPT)and the Special Thread (NS or national extra fine thread).

Figure 2-58

The bottoming, plug and taper taps shown here are identical in the size of the thread and the length of the tap. Their only difference is in the chamfered (tapered) threaded portion, Figure 2-58 (D), at the end of the tap. When the thread must be cut to the very bottom of a blind hole, all three taps are generally used; that is, thethread is started with the taper tap, Figure 2-58 (A), cut further into the hold with the plug tap, Figure 2-58 (B),and finished to the bottom of the hole with the bottoming tap, Figure 2-58 (C). The taper tap, Figure 2-58 (A),has the longest chamfer of all the taps and usually extends approximately 10 threads back from the point. Theplug tap, Figure 2-58 (B), has approximately a five-thread chamfer, while the bottoming tap has a one-threadchamfer.


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Figure 2-59

The bottoming tap, Figure 2-59 (A), is used when it is necessary to cut full threads to the bottom of a closedhole (a hole which has not been drilled through the material). Plug taps, Figure 2-59 (B), or bottoming tapsshould never be used to start a thread. The plug tap, Figure 2-59 (B), is used when one end of the hole is closed and a full thread is not required at thebottom of the hole. The taper tap, Figure 2-59 (C), is used to start all threads and may be used to finish the tapping operation whenthe tap can be run entirely through the material. The machine screw tap, Figure 2-59 (E), is used for fine-thread, small-diameter tapping operations. Thecone-shaped end, Figure 2-59 (D), of the material screw tap is made that way for manufacturing purposes andis usually found at the threaded end of small taps only. The machine screw tap also comes in the bottomingtap, plug tap and taper tap.

Tap TermsAdditional terms must be known before proceeding with the discussion oftaps. The more important tap terms are explained here. Refer to Figure2-61. Square: The squared end (A) at the top of the tap.Axis of Tap: An imaginary line (B) passing through the exact center alongthe full length of the tap.Shank: The part (C) behind the threaded and fluted section (D) of the tap.Chamfer: The tapered outside diameter (E) at the front end of thethreaded section.Cutting Face: The front of the land (F) of the threaded section.Flute: The four grooves or flutes (G) provided for the cutting faces (H) ofthe threads for chip passage and lubrication.External (Male) Center: The cone-shaped end (I) of the tap. It is usedfor manufacturing purposes in holding the tap and is usually found at thethreaded end of small taps only.Internal (Female) Center: A small drilled, countersunk hole (J) at theend of the tap necessary for manufacturing purposes.


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Body: The threaded and fluted section (D) of the tap.

Figure 2-60 Figure 2-61Hand-Operated DiesThe threading die is a tool used in cutting external threads. Generally speaking, the threading die is constructedto permit the cutting edges of four cutters or chasers to do an equal share in cutting a thread on a cylindrical(round) rod. Some dies are made solid, some are split to provide a thread adjustment and other dies are in two halves whichfit into a special handle. Solid dies have no means of adjustment to control the fit of the thread they cut and forthis reason are seldom used. The most popular dies for hand use today are the adjustable round split type. The two most used forms of adjustable round split dies are the open-adjusting type (A) on Figure 2-62 and thescrew-adjusting type (B) on Figure 2-62. Tightening the adjusting screw, Figure 2-62 (C), of the screw-adjusting type of die forces the split opening, Figure 2-62 (D), of this die wider apart, causing a thread of lesserdepth to be cut. When using the open-adjusting type of die, the depth of cut is regulated by tightening a seriesof set screws in the die handle. This process will be explained later. Dies are available for cutting threads for all standard bolt, screw and pipe sizes, such as NC, NF, machinescrew, pipe and other special threads.


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Figure 2-62 Die HandlesThe most common die handles used with adjustable round split dies are shown in Figure 2-63. The die isplaced in the opening, Figure 2-63 (E), (with recess (B) on Figure 2-63 facing set screw(s) with recess) of thedie handle. The die is locked securely in position by one or more set screws, Figure 2-63 (C). The singleset-screw type of handle, Figure 2-63 (D), is designed to accommodate round dies of the screw-adjusting type,Figure 2-63 (A). The set screw in the die handle is located in such a position that it enters a recess, Figure 2-63(B), provided for it in the side of the die. The die will fit in the handle closely, thus finger pressure on the setscrew is sufficient to secure it firmly. The three-screw kind of handle, Figure 2-63 (F), is designed to hold round, adjustable dies of any construction,although they are specifically manufactured for holding dies of the open-adjusting type, Figure 2-63 (G). Tightening the three set screws, Figure 2-63 (C), secures the die in place and also exerts sufficient pressure atthe right points to close the die teeth for a deeper cut.

Figure 2-63 Using the Hand DieThe correct method of holding and operating thread-cutting dies is as follows: It is important that the part being threaded by supported securely so it will not move during the threading


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process. Before using adjustable dies, always check first to see that the die is properly set. Never assume thatthe die is set correctly for the thread it is required to cut. To be safe, back off the adjusting screw(s) and makea trial cut on the rod to be threaded. Then test the fit of the thread on a nut or other internal thread into whichit is to be screwed. If the fit is too tight, turn the adjusting screw(s) on the die head (or die handle) so a deeper cut will be takenwith the next trial cut. After running the die over the threads again, make another trial fit and repeat thisprocedure until the threads have been cut to the correct depth. Remember, when too much metal has beencarelessly removed by a single cut of too great a depth, it is too late to correct the error. The damage is done. Note: Be sure to keep the die handle straight on the material being cut or damage to the material can result.

Figure 2-64

When cutting a thread on a rod, make sure the die is set properly. Place the tapered ends of the die, Figure2-64 (A), on the rod. Then turn the die handle slowly in a clockwise direction. The die should be backed offafter every two or three turns to break the chips, and lubricant should be applied freely to the dies in the samemanner as for taps. In cutting, the die operates just like the tap. The chips that are formed in the cutting are eliminated with thelubricant down the flutes, Figure 2-64 (B), of the die. Helpful Hint: When it is necessary to cut the full depth of thread up to the very end of a rod or bolt, first cutthe thread as far down as possible in the usual manner. Then back the die completely off, reversing it in thehandle so the tapered end of the die points away from the rod or bolt. Rethread it on the rod or bolt and turn itall the way down as far as possible. Never attempt to use the die in this manner without first having started thethread in the conventional way described above; this would be the same as using a bottoming tap in a holewithout preceding it with a taper or plug tap.


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TAP DRILL SIZES

NATIONAL COARSE THREAD SERIES MEDIUM FIT, CLASS 3 (NC)

Size and threads Dia. of body Body drill Preferred dia. of hole Tap drill

1-642-563-484-405-40

6-328-32

10-2412-241/4-20

5/16-I63/8-16

7/16-14½-13

9/16-12

5/8-11¾-107/8-91-8

.073

.086

.099

.112

.125

.138

.164

.190

.216

.250

.3125.375

.4375.500

.5625

.625

.750

.875I.000

4742373129

2718102

1/4

5/163/8

7/16½

9/16

5/8¾

7/81

.0575

.0682.078.0866.0995

.1063.1324.1476.1732.1990

.2559.3110.3642.4219.4776

.5315.6480.7307.8376

No. 53No. 515/64 in.No. 44No. 39

No. 36No. 29No. 26No. 17No. 8

F

5/16 in.U

27/64 in.31/64

17/32 In.41/64 in.49/64 in.

7/8 in.

NATIONAL FINE THREAD SERIES MEDIUM FIT, CLASS 3 (NF)

Size andthreads

Dia. of bodyBodydrill

Preferreddia. of hole

Tap drill

0-801-722-643-564-48

5-446-408-36

10-3212-28

1/4-28

5/16-243/8-24

7/16-201/2-20

9/16-185/8-183/4-167/8-141-14

.060

.073

.086

.099

.112

.125

.138

.164

.190

.216

.250.3125.375

.4375.500

.5625.625.750.875I.000

5247423731

292718102 F

5/163/8

7/16½

9/165/8¾

7/81

.0472

.0591

.0700

.0810

.0911

.1024.113.136.159.180

.213.2703.332.386.449

.506.568.6688.7822.9072

3/64 in.No. 53No. 50No. 46No. 42

No. 38No. 33No. 29No. 21No. 15

No. 3

IQW

7/16 in.

1/2 in.9/16 in.

1 1/16 in.5 1/64 in.59/64 in.

NATIONAL TAPER PIPE THREAD

Size pipethread, in.

No. oftlireadsper inch

Outside dia. of pipe for threadingSize pipe

reamer, in.Size tap drill, in.Decimal

inch

Nearestfractionof inch

1/8¼

3/81/23/4

2718181414

.405

.540

.675

.8401.050

13/3235/6443/6437/3213/64

1/8¼

3/8½¾

21/647/169/16

45/6429/32

REAMERS


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It is seldom possible to produce a hole that is perfectly straight and exactly the same diameter as a drill. Forcertain types of work, slight inaccuracies in producing holes are of little importance and the finished holesproduced with drills are satisfactory. On the other hand, when a high degree of accuracy is required, othermeans must be used to finish the holes. The most common method of doing this is by reaming.

Figure 2-65

When reamers are used for the accurate sizing of holes, the material is first drilled to a few thousandths of aninch under the desired size and then finished to the exact diameter with a reamer.

Figure 2-66Reamers are classified into two types: the hand reamer, Figure 2-66 (D), and the machine reamer, Figure 2-66(E). As the name implies, the hand reamer, Figure 2-66 (D), is used by hand. The shank, Figure 2-66 (C), is straightand has a square tang so it can be held and operated with a wrench (usually a tap handle). Reamer (E) onFigure 2-66 has a tapered shank and is used in power machines such as a drill press or lathe. The hand reamercan always be identified by its square tang. The small area (B)on Figure 2-66 is called the neck and (A) onFigure 2-66 is the body of the reamer. Hand reamers are available with tapered flutes, Figure 2-66 (F), orspiral flutes, Figure 2-66 (H). The flutes of a reamer area similar to those used in drills. They extend along the length of the body betweenthe blades, which form the cutting edges of the tool, and provide chip space when cutting. The shank, Figure2-66 (C), of a straight reamer is always one or two thousandths of an inch smaller in diameter than the body,Figure 2-66 (A), of the reamer, so the reamer can pass completely through the holes it makes without bindingon the shank.The spiral reamer, Figure 2-66 (G), yields the best results. This reamer will not chatter (vibrate) during thereaming operation. The straight-fluted reamer, Figure 2-66 (D), will occasionally chatter and produce anout-of-round hole by gouging out pieces of metal along the length of the hole. Spiral-Flute Reamers


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Figure 2-67

A much superior cutting action is obtained with spiral-flute reamers, Figure 2-67 (F), since the angle of thecutting edge to the work procedures a shearing cut and reduces the tendency of the tool to chatter. Also, incertain instances a hole, Figure 2-67 (B), to be reamed may have had a keyway, Figure 2-67 (A), machined init. In such a case it would be impossible to ream the hole with a straight-flute reamer, Figure 2-67 (G), becausethe cutting edges of the reamer would fall into the keyway, Figure 2-67 (A), jamming or breaking the reamer. A spiral-flute reamer, Figure 2-67 (F), however, permits its cutting edges to pass over a keyway withoutdifficulty. Spiral-flute reamers are made with either a right-, Figure 2-67 (E), or left-handed, Figure 2-67 (D), spiral toadapt to different types of work. A right-hand spiral, Figure 2-67 (E), turns to the right, or clockwise, when viewed from the end, Figure 2-67(C), of the reamer; a left-hand spiral, Figure 2-67 (D), turns in the opposite direction. ALWAYS operate the reamer in a right-handed or clockwise direction, whether it has a right- or left-handspiral. A left-hand spiral is best suited for most types of work, since the direction of the spiral resists the feed of thereamer into the work C a desirable feature. A right-hand spiral tends to draw the reamer into the work so thatit advances too rapidly and causes the cutting edges to take more of a cut than they can stand. Expandable Hand Reamers

Figure 2-68

Expandable hand reamers are used where the fitting of parts in a final assembly is required. The expansionreamer, Figure 2-68 (D), is made of a solid piece of tool steel and has from three to six slots, Figure 2-68 (C),cut in the bottoms of the flutes around the body. These slots extend into the hollow center of the tool, which isdrilled and reamed on a slight taper. A screw, Figure 2-68 (A), with a tapered end screws into the body, Figure2-68 (B), of the reamer. When the screw is forced against the inner, tapered portion, it pushes out or expandsthe blades of the reamer. The second type of expansion reamer, Figure 2-68 (J), is the adjustable blade reamer. The body of the reameris threaded, Figure 2-68 (I), throughout its entire length. Tapered slots to receive the blades are also machinedon the reamer body, Figure 2-68 (G). The blades are tapered along one edge to correspond with the taperedslots. Once in position, the cutting edges of blades opposite each other are parallel. The diameter of the reamer blades, Figure 2-68 (G), is set by means of the adjusting nuts, Figure 2-68 (E) and(H), which also hold the blades in the slots, Figure 2-68 (F). By loosening one nut and tightening the other, the


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blades can be moved in either direction. Moving the blades in the direction of the threaded shank, Figure 2-68(I), expands them. One complete revolution of the adjusting nuts, Figure 2-68 (E) and (H), expands orcontracts the reamer approximately four thousandths of an inch. The expansion reamer is used by mechanics. It is useful in assembling parts where bushings must be reamed to suit the size of pins, spindles, etc. Eachreamer has sufficient expansion to increase its diameter to the next larger size reamer.How to Use Hand Reamers

Figure 2-69When a hole is to be reamed by hand, first place the tapered end, Figure 2-69 (A), of the reamer, Figure 2-69(B), in the hole, Figure 2-69 (G). Then apply a wrench, Figure 2-69 (C), usually a tap handle, to the squaretang, Figure 2-69 (D), of the reamer. Next, set the reamer square with the work (at right angles to thematerial). If the top of the work is flat, place a square, Figure 2-69 (E), against the side of the reamer. Checkthe reamer position again, 90°, Figure 2-69 (H), from the first position. The blades of the reamer should beexactly parallel with the blade of the square, Figure 2-69 (E), in each position. If the top of the work is not flat,the reamer must be aligned to the hole by sight. In this case it is sighted from two positions, 90° apart.


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After the reamer, Figure 2-69 (J), has been aligned to the hole, turn it slowly and carefully with the wrench,Figure 2-69 (I), in a right-hand or clockwise direction. Note: Never turn a reamer to the left. They are made to turn to the right and will not cut when turned in thereverse direction. Turning a reamer to the left dulls the cutting edges of the blades. When the reamer has been turned slightly, check it again from two positions 90° apart to be sure it is startingstraight. Continue in this manner, applying an even pressure to the wrench, Figure 2-69 (I), with both hands sothe reamer will not move to one side while turning it. Allowing the reamer to move to one side will result in anoversized hole. Reamer Positive Rake and Negative Rake

Figure 2-70 When a reamer is to be used in soft metal such as aluminum, the tooth, Figure 2-70 (A), is cut on a line, Figure2-70 (B), back of the reamer center point, Figure 2-70 (C), to produce what is known as a positive rake angle. The cutting edge formed is quite sharp and enables the reamer to cut freely. In negative rake angle, the line, Figure 2-70 (D), of the cutting edge falls ahead of the reamer center point,Figure 2-70 (E). This type of construction provides a strong cutting edge and is used for cutting very hardsteel. The negative-reamer rake is also used for removing brass, even though it is a soft metal, because the negativerake prevents the tool from becoming clogged or gouging into the work. This rake produces a scraping ratherthan a cutting action; the cutting edges do not bite deeply into the metal. Care of ReamersThe quality of the finish and accuracy of holes produced, as well as the useful life of the reamer, depend to avery large extent on the care the tool receives both in operation and in storage. The smallest burr on thecutting edge, Figure 2-71 (A), of a reamer will produce a rough hole; therefore, a reamer must always beinspected by feeling along the cutting edge. If any burrs are found, they must be removed with an oilstone.

Figure 2-71

Always use a lubricant such as lard oil when reaming steel. Lard oil is also used in reaming aluminum andmonel metal. Oil should be applied when working brass, bronze and copper, though bronze is sometimesreamed dry. Lubricant is not generally used in reaming cast iron.


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Never start a reamer on an uneven surface. The reamer will tend to drift toward the point of least resistance. This not only produces a hole that is out-of-round and otherwise lacking in trueness, but also subjects thereamer to severe strains. Never stack reamers in bins or tool boxes without some separating layer of cardboard or wood. The edges areso hard and sharp that even a light impact against each other or some other hard object will chip the edges. Individual cardboard or plastic tubes make excellent holders for reamers in storage. See that reamers are properly coated with oil when not in use to prevent rusting at the cutting edges. Even asmall rust spot will leave a pit or nick. If careful attention is given to the above precautions, your reamer will have a long and useful life.


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aviation hand tools for cutting, drilling, machining

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