Care of Files There are several precautions that any good craftsman will take in caring for his files.
1. Choose the right file for the material and work to be performed.
2. Keep all files racked and separated so they do not bear against each other.
3. Keep the files in a dry place--rust will cor-
4. Keep files clean-Tap the end of the file against the bench after every few strokes, to loosen and clear the filings. Use the file card to keep files clean-a dirty file is a dull file.
Particles of metal collect between the teeth of a file and may make deep scratches in the material being filed. When these particles of metal are lodged too firmly between the teeth and cannot be removed by tapping the edge of the file, remove them with a file card or wire brush (figure 12-12).
Draw the brush across the file so that the bristles Card Pneumatic drills are preferred for use around flammable materials, since sparks from an electric drill are a fire or explosion hazard.
Twist Drills A twist drill is a pointed tool that is rotated to cut holes in material. It is made of a cylindrical hardened steel bar having spiral flutes (grooves) running the length of the body, and a conical point with cutting edges formed by the ends of the flutes.
Twist drills are made of carbon steel or highspeed alloy steel. Carbon steel twist drills are satisfactory for the general run of work and are relatively inexpensive. The more expensive highspeed twist drills are used for the tough materials such as stainless steels. Twist drills have from one to four spiral flutes. Drills with two flutes are used for most drilling; those with three or four flutes are used principally to follow smaller drills or to enlarge holes.
Lip or cutting edge Lip clearance (125°-135°) Brush Slot for pick . Flute Pick FIGURE 12-12. File Card. Land Drills There are generally four types of portable drills used in aviation for holding and turning twist Heel angle drills. Holes ¼ inch in diameter and under can be (12°-15° ) drilled using a hand drill. This drill is commonly called an "egg beater." The breast drill is designed Lip angle (normally 59°) to hold larger size twist drills than the hand drill.
In addition a breast plate is affixed at the upper Lips or cutting edges end of the drill to permit the use of body weight to increase the cutting power of the drill. Electrie and pneumatic power drills are available in various shapes and sizes to satisfy almost any requirement. FIGURE 12-13. Twist drill.
- Point
- Margin
- Flute Straight shank Size stamped here Taper shank Square shank (used in brace) FIGURE 12-14. Drills.
The principal parts of a twist drill are the shank, the body, and the point, illustrated in figure 12-13.
The drill shank is the end that fits into the chuck of a hand or power drill. The two shank shapes most commonly used in hand drills are the straight shank and the square or bit stock shank (figure 12-14). The straight shank generally is used in hand, breast, and portable electric drills;
the square shank is made to fit into a carpenter's brace. Tapered shanks generally are used in machine shop drill presses.
The metal column forming the core of the drill is the body. The body clearance area lies just back of the margin, slightly smaller in diameter than the margin, to reduce the friction between the drill and the sides of the hole. The angle at which the drill point is ground is the lip clearance angle.
On standard drills used to cut steel and cast iron, the angle should be 59° from the axis of the drill.
For faster drilling of soft materials, sharper angles are used.
The diameter of a twist drill may be given in one of three ways: (1) By fractions, (2) letters, or (3) numbers. Fractionally, they are classified by sixteenths of an inch (from 6 to 3½ in.), by thirty-seconds (from ⅔2 to 2/½ in.), or by sixtyfourths (from 64 to 1¾ in.). For a more exact measurement a letter system is used with decimal equivalents: A (0.234 in.) to Z (0.413 in.). The number system of classification is most accurate:
No. 80 (0.0314 in.) to No. 1 (0.228 in.). Drill sizes and their decimal equivalents are shown in figure 12-15.
The twist drill should be sharpened at the first sign of dullness. For most drilling, a twist drill with a cutting angle of 118° (59° on either side of center) will be sufficient; however, when drilling soft metals, a cutting angle of 90° may be more efficient.
Typical procedures for sharpening drills (figure 12-16) are as follows:
1. Adjust the grinder tool rest to a convenient height for resting the back of the hand while grinding.
2. Hold the drill between the thumb and index finger of the right or left hand. Grasp the body of the drill near the shank with the other hand.
3. Place the hand on the tool rest with the center line of the drill making a 59° angle with the cutting face of the grinding wheel. Lower the shank end of the drill slightly.
4. Slowly place the cutting edge of the drill against the grinding wheel. Gradually lower the shank of the drill as you twist the drill in a clockwise direction. Maintain pressure against the grinding surface only until you reach the heel of the drill.
5. Check the results of grinding with a gage to determine whether or not the lips are the same length and at a 59° angle.
Reamers Reamers are used to smooth and enlarge holes to exact size. Hand reamers have square end shanks so that they can be turned with a tap wrench or similar handle. The various types of reamers are illustrated in figure 12-17.
A hole that is to be reamed to exact size must be drilled about 0.003- to 0.007-inch undersize. A cut that removes more than 0.007 inch places too much load on the reamer and should not be attempted.
Reamers are made of either carbon tool steel or high-speed steel. The cutting blades of a high-speed steel reamer lose their original keenness sooner than those of a carbon steel reamer; however, after the first super-keenness is gone, they are still serviceable. The high-speed reamer usually lasts much longer than the carbon steel type.
Milli- Meteı ............. Frac- Num tional ber ........ Frac- tional Num ber Milli- Meter Equiv. tional ber Dec. Frac-Num Milli- Dec. Frac- Num bes 22 .2677 .15 50 .2716 .2 21 .2720 .25 20 .2756 .3 49 .2770 J 80 .2795 .35 48 19 .2811 79 .2812 9/32 .39 1/64 5/64 .2835 47 18 .2854 78 11/64 .2874 .45 17 .2900 77 46 .5 45 16 .2950 76 75 15 19/64 .55 44 74 14 .3020 IN 13 43 3/16 12 42 11 5/16 3/32 10 69 41 .75 68 40 8 P .79 1/32 39 7 13/64 21/64 6 .85 37 Q 5 .9 36 R 7/64 .95 35 11/32 62 3 34 33 1/32 S 32 2 T 31 23/64
1.1 ı/8
1.15 .19 3/64 30 .95 15/64 U B 29 3/8 55 78 28 54 9/64 D 27 1/4 W 26 F 1/16 25 .3937 G 52 24 .4040 Y
1.65 17/64
1.7 23 .4130 51 5/32 H .4134 FIGURE 12-15. Drill sizes.
Straight reamer (Hand) Spiral taper reamer Taper reamer (Power) (Hand) Straight reamer (Power) Expansion reamer Adjustable reamer FIGURE 12-17. Reamers.
Reamer blades are hardened to the point of being brittle and must be handled carefully to avoid chipping them. When reaming a hole, rotate the reamer in the cutting direction only.
Turn the reamer steadily and evenly to prevent chattering, or marking and scoring of the hole walls.
Reamers are available in any standard size. The straight-fluted reamer is less expensive than the spiral-fluted reamer, but the spiral type has less tendency to chatter. Both types are tapered for a short distance back of the end to aid in starting.
Bottoming reamers have no taper and are used to complete the reaming of blind holes.
For general use, an expansion reamer is the (D) (E) 12°-15° most practical. This type is furnished in standard sizes from ¼ inch to l inch, increasing in diameter by ⅓2-inch increments.
Taper reamers, both hand- and machineoperated, are used to smooth and true tapered holes and recesses.
Countersink A countersink is a tool which cuts a coneshaped depression around the hole to allow a rivet or screw to set flush with the surface of the material. Countersinks are made with various FIGURE 12-16. Drill sharpening procedures. angles to correspond to the various angles of the 541
Cutter shaft Cutter Pilot Body
• Lock nut 100° Stop Chip opening Standard countersink Stop countersink Fiber collar FIGURE 12-18. Countersinks.
countersunk rivet and screwheads. The angle of the 7/18 - - 9/16 standard countersink shown in figure 12-18 is 100°. 5/167 • 11/16 Special stop countersinks are available. Stop 3/16 - - 13/16 countersinks (figure 12-18) are adjustable to any desired depth, and the cutters are interchangeable 1/16 - 15/16 so that holes of various countersunk angles may be made. Some stop countersinks have a micrometer set arrangement (in increments of 0.001 inch) 2 for adjusting the cutting depths.
When using a countersink, care must be taken not to remove an excessive amount of material since this reduces the strength of flush joints.
1/8.
LAYOUT AND MEASURING TOOLS • 7/8 3/8 3/4 Layout and measuring devices are precision tools. They are carefully machined, accurately 1/2 5/8 marked and, in many cases, are made up of very 3/64 5/64 delicate parts. When using these tools, be careful not to drop, bend, or scratch them. The finished product will be no more accurate than the 1/64 - 7/64 measurements or the layout; therefore, it is very important to understand how to read, use, and care for these tools.
32 Rules Rules are made of steel and are either rigid or flexible. The flexible steel rule will bend, but it 1/32- • 6/32 should not be bent intentionally as it may be broken rather easily. 2/32 - 5/32 In aircraft work the unit of measure most commonly used is the inch. The inch may be 3/32 4/32 divided into smaller parts by means of either common or decimal fraction divisions. The frac- FIGURE 12-19. Rules.
Scriber Level Protractor head
• Center head Stock head FIGURE 12-20. Combination set.
tional divisions for an inch are found by dividing the inch into equal parts--halves (½), quarters (¼), eighths (⅛), sixteenths (%), thirty-seconds
32), and sixty-fourths (⅙4) -as shown in figure
12-17.
The fractions of an inch may be expressed in decimals, called decimal equivalents of an inch;
for example, ⅛ inch is expressed as 0.0125 (one hundred twenty-five ten-thousandths of an inch).
Rules are manufactured in two basic styles, those divided or marked in common fractions (figure 12-19) and those divided or marked in decimals or divisions of one one-hundredth of an inch. A rule may be used either as a measuring tool or as a straightedge.
Combination Sets The combination set (figure 12-20), as its name implies, is a tool that has several uses. It can be used for the same purposes as an ordinary trisquare, but it differs from the tri-square in that the head slides along the blade and can be clamped at any desired place. Combined with the square or stock head are a level and scriber. The head slides in a central groove on the blade or scale, which can be used separately as a rule.
The spirit level in the stock head makes it convenient to square a piece of material with a surface and at the same time tell whether one or the other is plumb or level. The head can be used alone as a simple level.
The combination of square head and blade can also be used as a marking gage to scribe lines at a 45° angle, as a depth gage, or as a, height gage.
A convenient scriber is held frictionally in the head by a small brass bushing.
The center head is used to find the center of shafts or other cylindrical work. The protractor head can be used to check angles and also may be set at any desired angle to draw lines.
Scriber The scriber is designed to serve the aviation mechanic in the same way a pencil or pen serves a writer. In general, it is used to scribe or mark lines on metal surfaces. The scriber (figure 12-21) is made of tool steel, 4 to 12 inches long, and has two needle-pointed ends. One end is bent at a 90° angle for reaching and marking through holes.
Before using a scriber always inspect the points for sharpness. Be sure the straightedge is flat on the metal and in position for scribing. Tilt the scriber slightly in the direction toward which it will be moved, holding it like a pencil. Keep the scriber's point close to the guiding edge of the straightedge. The scribed line should be heavy enough to be visible, but no deeper than necessary to serve its purpose.
FIGURE 12-21. Scriber.
Dividers and Pencil Compasses Dividers and pencil compasses have two legs joined at the top by a pivot. They are used to scribe circles and arcs and for transferring measurements from the rule to the work.
Pencil compasses have one leg tapered to a needle point; the other leg has a pencil or pencil Spring inside calipers lead inserted. Dividers have both legs tapered to needle points.
When using pencil compasses or dividers, the Hermaphrodite calipers following procedures are suggested:
1. Inspect the points to make sure they are sharp.
2. To set the dividers or compasses, hold them with the point of one leg in the graduations on the rule. Turn the adjustment nut with the thumb and forefinger;
adjust the dividers or compasses until the point of the other leg rests on the gradua- Firm joint screw tion of the rule which gives the required adjusting inside measurement. calipers
3. To draw an arc or circle with either the pencil compasses or dividers, hold the thumb attachment on the top with the thumb and forefinger. With pressure exerted on both legs, swing the compass in a clockwise direction and draw the desired arc or circle.
The tendency for the legs to slip is avoided by inclining the compasses or dividers in the direction in which they are being rotated. In working on metals, the dividers are used only to scribe arcs or circles that will later be removed by cutting. All other arcs or circles are drawn with pencil compasses to avoid scratching the material.
5. On paper layouts, the pencil compasses are used for describing arcs and circles.
Dividers should be used to transfer critical measurements because they are more accurate than a pencil compass.
Calipers Calipers are used for measuring diameters and distances or for comparing distances and sizes. The three common types of calipers are the inside, the outside, and the hermaphrodite calipers, such as gear-tool calipers. (See figure 12-22.)
Outside calipers are used for measuring outside dimensions, for example, the diameter of a piece of Spring outside calipers Firm joint screw adjusting outside calipers FICURE 12-22. Calipers.
round stock. Inside calipers have outward curved legs for measuring inside diameters, such as diameters of holes, the distance between two surfaces, the width of slots, and other similar jobs.
A hermaphrodite caliper is generally used as a marking gage in layout work. It should not be used for precision measurement.
Micrometer Calipers There are four types of micrometer calipers, each designed for a specific use. The four types are 544
Thread play Thimble cap Micrometer screw Fixed nut adjusting nut Anvil Spindie Measuring faces Barrel Thimble Ratchet stop Clamp ring Frame FIGURE 12-23. Outside micrometer.
commonly called outside micrometer, inside micrometer, depth micrometer, and thread micrometer. Micrometers are available in a variety of sizes, either 0 to ½ inch, 0 to 1 inch, 1 to 2 inch, 2 to 3 inch, 3 to 4 inch, 4 to 5 inch, or 5 to 6 inch sizes.
The outside micrometer (figure 12-23) is used by the mechanic more often than any other type.
It may be used to measure the outside dimensions of shafts, thickness of sheet metal stock, diameter of drills, and for many other applications.
The smallest measurement which can be made with the use of the steel rule is one sixty-fourth of an inch in common fractions, and one one-hundredth of an inch in decimal fractions. To measure more closely than this (in thousandths and ten-thousandths of an inch), a micrometer is used.
If a dimension given in a common fraction is to be measured with the micrometer, the fraction must be converted to its decimal equivalent.
All four types of micrometers are read in the same way. The method of reading an outside micrometer is discussed later in this chapter.
Micrometer Parts The fixed parts of a micrometer (figure 12-23) are the frame, barrel, and anvil. The movable parts of a micrometer are the thimble and spindle. The thimble rotates the spindle which moves in the threaded portion inside the barrel. Turning the thimble provides an opening between the anvil and the end of the spindle where the work is measured.
• The size of the work is indicated by the graduations on the barrel and thimble.
Reading a Micrometer The lines on the barrel marked 1, 2, 3, 4, etc., indicate measurements of tenths, or 0.100 inch,
0.200 inch, 0.300 inch, 0.400 inch, respectively (see figure 12-24).
Each of the sections between the tenths divisions (between 1, 2, 3, 4, etc.) is divided into four parts of 0.025 inch each. One complete revolution of the thimble (from zero on the thimble around to the same zero) moves it one of these divisions (0.025 inch) along the barrel.
The bevel edge of the thimble is divided into 25 equal parts. Each of these parts represents one twenty-fifth of the distance the thimble travels along the barrel in moving from one of the 0.025- inch divisions to another. Thus, each division on the thimble represents one one-thousandth (0.001) of an inch. These divisions are marked for convenience at every five spaces by 0, 5, 10, 15, Barrel Thimble .300 .200→ → 100 / 1/10 of an inch Horizontal line FIGURE 12-24. Micrometer measurements.
and 20. When 25 of these graduations have passed the horizontal line on the barrel, the spindle (baving made one revolution) has moved 0.025 inch.
The micrometer is read by first noting the last visible figure on the horizontal line of the barrel representing tenths of an inch. Add to this the length of barrel between the thimble and the previously noted number. (This is found by 20 multiplying the number of graduations by 0.025 .025 inch.) Add to this the number of divisions on the = .150 -.100 → .025 bevel edge of the thimble that coincides with the line of the graduation. The total of the three (A) .150 in. figures equals the measurement. (Figure 12-25 shows several sample readings.)
Vernier Scale Some micrometers are equipped with a vernier 001 scale which makes it possible to read directly the fraction of a division that may be indicated on the thimble scale. Typical examples of the vernier scale as it applies to the micrometer are shown in figure 12-26.
.025 = .151 All three scales on a micrometer are not fully
- .100 - .025 visible without turning the micrometer; but the examples shown in figure 12-26 are drawn as (B) .151 in though the barrel and thimble of the micrometer were laid out flat so that all three scales can be seen at the same time. The barrel scale is the lower horizontal scale; the thimble scale is vertical on the right; and the long horizontal lines (0 through 9 and 0) make up the vernier scale.
09670990414 (C) .160 in. 20 20 Barrel scale
0.2947
0.2944 20 15 (D) .175 in.
0.2153 0.1005 FIGURE 12-25. Reading a micrometer. FIGURE 12-26. Vernier scale readings.
In reading a micrometer, an excellent way to remember the relative scale values is to remember that the 0.025-inch barrel scale graduations are established by the lead screw (40 threads per inch). Next, the thimble graduations divide the
0.025 inch into 25 parts, each equal to 0.001 inch;
then the vernier graduations divide the 0.001 inch into 10 equal parts, each equal to 0.0001 inch.
Remembering the values of the various scale Adjusting screw graduations, the barrel scale reading is noted. The thimble scale reading is added to it; then the A Adjustable round split die vernier scale reading is added to get the final reading. The vernier scale line to be read is always the one aligned exactly with any thimble graduation.
In the first example in figure 12-26, the barrel reads 0.275 inch and the thimble reads more than
0.019 inch. The number 1 graduation on the thimble is alined exactly with the number 4 graduation on the vernier scale. Thus, the final reading is 0.2944 inch.
In the second example in figure 12-26, the barrel reads 0.275 inch, and the thimble reads more than 0.019 inch and less than 0.020 inch. On the vernier scale, the number 7 graduation coincides with a line on the thimble. This means that the thimble reading would be 0.0197 inch. Adding this to the barrel reading of 0.275 inch gives a total measurement of 0.2947 inch.
The third and fourth examples in figure 12-26 are additional readings that would require use of the vernier scale for accurate readings to tenthousandths of an inch.
Using a Micrometer The micrometer must be handled carefully. If it is dropped, its accuracy may be permanently affected. Continually sliding work between the Taper B Plain round split die FIGURE 12-28. Types of dies.
anvil and spindle may wear the surfaces. If the spindle is tightened too much, the frame may be sprung permanently and inaccurate readings will result.
To measure a piece of work with the micrometer, hold the frame of the micrometer in the palm of the hand with the little finger or third finger, whichever is more convenient. This allows the thumb and forefinger to be free to revolve the thimble for adjustment.
TAPS AND DIES A tap is used to cut threads on the inside of a hole, while a die is for cutting external threads on round stock. They are made of hard-tempered steel and ground to an exact size. There are four types of threads that can be cut with standard taps and dies. They are: National Coarse, National Fine, National Extra Fine, and National Pipe.
Hand taps are usually provided in sets of three taps for each diameter and thread series. Each set contains a taper tap, a plug tap, and a bottoming tap. The taps in a set are identical in diameter and cross section; the only difference is the amount of taper (see figure 12-27).
Plug The taper tap is used to begin the tapping process, because it is tapered back for 6 to 7 threads. This tap cuts a complete thread when it is cutting above the taper. It is the only tap needed when tapping holes that extend through thin Bottoming sections. The plug tap supplements the taper tap FIGURE 12-27. Hand taps. for tapping holes in thick stock.
The bottoming tap is not tapered. It is used to cut full threads to the bottom of a blind hole.
Dies may be classified as adjustable round split die, and plain round split die (see figure 12-28).
The adjustable-split die has an adjusting screw Tap wrenchs. that can be tightened so that the die is spread slightly. By adjusting the die, the diameter and fit of the thread can be controlled.
Diestock Solid dies are not adjustable; therefore, a variety of thread fits cannot be obtained with this type.
There are many types of wrenches for turning taps, as well as turning dies. The T-handle, the adjustable tap wrench, and the diestock for round split dies shown in figure 12-29 are a few of the more common types.
Information on thread sizes, fits, types, etc., is FIGURE 12-29. Diestock and tap wrenches. shown in figs. 12-30, 12-31 and 12-32.
NATIONAL COARSE THREAD SERIES NATIONAL FINE THREAD SERIES MEDIUM FIT. CLASS 3 (NC) MEDIUM FIT. CLASS 3 (NF) Tap Drill Tap Drill Dia. of Dia. of Size hody Pref'd Nearest Size body Pref'd Nearest and for Body dia. of stand'd and for Body dia. of stand'd Threads thread hole Drill Size threads thread Drill hole Drill Size 0-80 .060 52 .0472 3/64 1-64 .073 47 .0575 #53 1-72 .073 47 0591 #53 2-56 .086 42 .0682 #51 2-64 .086 42 0700 #50 3-48 _099 37 .078 5/64 3-56 .099 37 0810 #46 4-40 .112 31 0866 #44 4-48 .112 31 0911 #42 5-40 125 29 0995 #39 5-14 .125 25 .1024 #38 6-32 138 27 1063 #36 6-40 .138 27 113 #33 8-32 .164 18 1324 #29 8-36 .164 18 136 #29 10-24 .190 10 .1472 #26 10-32 .190 10 159 #21 12-24 .216 2 .1732 #17 12-28 .216 2 .180 #15 1/4-20 .250 • 1/4 .1990 #8 1/4-28 .250 F .213 #З 5/16-18 .3125 5/16 .2559 #F 5/16-24 .3125 5/16 .2703 3/8-16 375 3/8 .3110 5/16" 3/8-24 375 3/8 .332 7/16-14 .4375 7/16 .3642 7/16-20 .4375 7/16 .386 1/2-13 .500 1/2 .4219 27/64" 1/2-20 .500 1/2 449 7/16" 9/16-12 .5625 9/16 .4776 31/64" 9/16-18 .5625 9/16 ,506 1/2" 5/8-11 .625 5/8 .5315 17/32" 5/8-18 625 5/8 .568 9/16" 3/4-10 750 3/4 .6480 41/64" 3/4-16 .750 3/4 .6688 11/16" 7/8-9 .875 7/8 .7307 49/64" 7/8-14 .875 7/8 .7822 51/64" 1-8 1.000 1.0 .8376 7/8" 1-14 1.000 I.0 .9072 49/64" FIGURE 12-30. American (National) screw thread sizes.
Tap Drills for Pipe Threads Diameter Length Size Drill 27 R 18 18 14 14 8 3-1/2 8 4 4.38712 1.3000 844 4.500 4.23438 4-1/4 FIGURE 12-31. American (National) pipe thread dimensions and tap drill sizes.
Diameter Soft Mild Malleable Hard Cast Tool or Alloy Steel of Drill Metals Steel Iron Iron Hard Steel Cast Steel 300 F.P.M. 100 F.P.M. 90 F.P.M. 80 F.P.M. 60 F.P.M. 40 F.P.M.
1/16 (No. 53 to 80) 18320 3667 2445 3/32 (No. 42 to 52) 122:2 2442 1649 1/8 (No. 31 to 41) 9180 1833 1222 5/32 (No. 23 to 30) 7328 1465 977 3/16 (No. 13 to 22) 6106 1222 815 7/32 (No. I to 12) 5234 1047 698 1/4 (A to E) 4575 917 611 9/32 (G to K) 4071 814 542 9/16 (L, M, N) 3660 733 489 11/32 (O to R) 3330 666 444 3/8 (S, T, U) 3050 611 407 13/32 (V to Z) 2818 563 376 7/16 2614 1222 524 349 15/32 2442 1140 652 488 326 1/2 2287 1528 1070 764 688 611 458 306 9/16 2035 1357 950 678 611 543 407 .: 271 3/8 1830 1222 856 611 550 489 367 244 11/16 1665 1110 777 555 500 444 333 222 3/4 1525 1018 713 509 458 407 306 204 Figures are for High-Speed Drills. The spced of Carbon Drills should be reduced one-half.
Use drill speed nearest to figure given.
FIGURE 12-32. Drill speeds.