    [Fundamentals of Mechanical Drawing]
    [From the U.S. Government Publishing Office, www.gpo.gov]

    ﻿W i.-bS: I -1OSO
    Document Reserve
    TM 1-1050
    a
    WAR DEPARTMENT
    TECHNICAL MANUAL
    FUNDAMENTALS OF MECHANICAL DRAWING
    March 24, 1943
    NON-CIRCULATING
    LIBRARY
    OF
    NORTH TEXAS
    STATE TEACHERS COLLEGE
    DENTON, TEXAS
    TM 1-1050
    1
    TECHNICAL MANUAL No. 1-1050
    WAR DEPARTMENT, Washington, March 24,1943.
    FUNDAMENTALS OF MECHANICAL DRAWING
    Paragraphs
    Section I. General_____________________________________________ 1
    II.	Equipment and materials________________________ 2-16
    III.	Lettering and lines_____________________________17-18
    IV.	Geometric constructions_________________________19-34
    V.	Orthographic projection_________________________35-37
    VI.	Pictorial drawing_______________________________38-42
    VII.	Sectional views and threaded parts______________43-44
    VIII.	Scales, dimensions, and notes___________________45-47
    IX.	Technical sketching_______________________________ 48
    X.	Sheet metal drafting____________________________49-52
    XI.	Representative working drawings___________________ 53
    Section I
    GENERAL
    Paragraph General____________________________________________________________ 1
    1.	General.—a. (1) The design, construction, and repair of machines or structures involve a mass of detail with respect to specific parts. A complete written or oral description of detailed units would necessitate a lengthy, complex discussion which would tend to confuse and retard the progress of the workman. It is more efficient to present the various design1 features in the form of a drawing, showing various views, so that details of construction may be readily interpreted. The use of a drawing containing dimensions, notes, etc., for further simplification, presents to the workman clear, concise information.
    (2)	A drawing is made with the aid of instruments and other equipment, in which form it is known as a mechanical drawing, or it is made as a freehand sketch. The execution of such drawings requires skill, accuracy, and an understanding of the subject matter. In the various industries, practices may vary as to the manner of presentation of information in mechanical drawings, but the manner of execution of such drawings is common to all.
    513393°—43-1	1
    127947
    1
    ARMY AIR FORCES
    ______________________________________ SUPPLIES AND EQUIPMENT CLASSIFICATION let,	change	date CHECKER
    PATENT CLAUSE	___________________________________________________
    _____________________I_____________________________
    UNLESS OTHERWISE SPECIFIED DIMENSIONS ARE IN INCHES, LIMITS ON FRACTIONS	DECIMALS	ANOLES	------------------------------------------------------------
    Gf BUFF	ROUGH MACH FINISH_____________________________________________________________________________
    (gf HAND FINISH	of ROUGH FILE OR GRIND material finish [draftsman checker eng examined prooapp ho, refused on next assem.
    (ffSMOOTH MACH FINISH & SAND BLAST	AA* CORPS
    (jf REMOVE FINS ANO SPRUES	materiel div
     FINISH ALL SURFACES NOT OTHERWISE SPECIFIED. HEAI TREAT DRAW,NG S,ZE -------------------------- p.cce number
    Figure 1.—Army Air Forces drawing form.
    2
    127947
    FUNDAMENTALS OF MECHANICAL DRAWING	1
    (3)	The purpose of this manual is to familiarize the student mechanic with the basic principles of mechanical drawing and general practices relevant thereto. Only subject matter considered essential for use in basic courses in mechanical drawing has been included. Tables of limits, classes of fits, standard dimensions of threads, etc., have been omitted, as such subject matter more appropriately pertains to the more advanced and specialized courses in drafting. When the need arises for information of this type, reference should be made to handbooks containing such tables.
    b.	As a rule, the use of original drawings would be impractical. The circulation of the drawing would be limited and would soon be destroyed or rendered illegible as a result of wear. Therefore, duplicates are prepared for use in the work of production, maintenance, etc. The drawing is first traced in ink or pencil, using translucent cloth or paper; or in some instances, the original drawing is executed on tracing paper. The drawing may be duplicated by exposing it to an intense light while in contact with an especially prepared sensitized paper. After exposure to the light, the exposed paper is treated with certain chemicals which develop the image. There are numerous printing processes and types of paper which may be used for drawing reproduction. The final product or print may have white lines on a blue background, white lines on a brown background, black lines on a white background, or red lines on a white background, depending upon the process and type of paper used. Blueprints, Van Dyke prints, Ozalid prints, and photostat prints are some of the most common types of reproductions.
    c.	(1) There apparently is little uniformity in the size of drawings. In many instances the size of the sheet is selected to suit the object to be drawn. Often, however, the standard letter-size sheet of 8% by 11 inches is used for small drawings. For larger drawings, multiples of this size, as shown below, are used. This range facilitates folding prints into suitable sizes for filing in letter-size filing cabinets. The 42-inch size is an exception, but is used for purposes of economy.
    Width (inches)		8H	11	11	17	17	17	22	25	34	34	34	42	42
    Length (inches)		11	17	34	22	42	66	34	42	42	66	88	66	88
    (2)	In addition to dimensions and notes, certain other data are associated with a drawing. These data usually include the title, number, scale, material, finish, changes, patent clauses, etc., set out in blocks. Figure 1 shows the arrangement of such data on a drawing form used by the Army Air Forces.
    d.	The subject matter and illustrations contained in this manual,
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    1-3
    ARMY AIR FORCES
    with respect to line work, arrangement of views, symbols, sectional views, dimensioning, and screw thread representation, is generally in accordance with principles approved by American Standards Association in publication entitled “American Standard Drawings and Drafting Room Practice.” 1
    Se	ction II
    EQUIPMENT AND MATERIALS 2
    Paragraph
    Drawing board____________________________________________________________ 2
    Paper and cloth__________________________________________________________ 3
    Pencils____________________________________________________________.____ 4
    Erasers__________________________________________________________________ 5
    T-square_________________________________________________________________ 6
    Triangles---------------------------------------------------------------- 7
    Irregular curve__________________________________________________________ 8
    Triangular scale________________________________________________________  9
    Protractor-------------------------------------------------------------- 10
    Ruling pen-------------------------------------------------------------- 11
    Lettering pens________________________________________________________   12
    Compass_________________________________________________________________ 13
    Dividers________________________________________________________________ 14
    Bow instruments_________________________________________________________ 15
    Care of equipment------------------------------------------------------  16
    2.	Drawing board.—A drawing board or table is used to provide a flat, smooth surface for the paper while the drawing is being made, and also provides a straight edge for guiding the T-square. A typical drawing board, with T-square and drawing paper in place, is shown in figure 2.
    3.	Paper and cloth.—a. Drawing paper is available in a variety of grades, in sheets or rolls, in colors of white, cream, or buff. For general pencil work, a paper with slight grain and good erasing qualities is desirable. Thin, tough, translucent paper which is transparent with close contact is used to trace copies in pencil or ink. Tracing paper is also used for original pencil drawings. Fine linen cloth, treated so as to make it translucent and smooth, is generally used for ink tracing. The dull side of the cloth is used and, prior to inking, the surface is lightly sprinkled and rubbed with powdered chalk or soapstone. Where an erasure has been made, the cloth is again treated with chalk or soapstone.
    b. The paper should be placed with one edge near the left edge of
    1 Permission granted by American Society of Mechanical Engineers.
    2 The subject matter and illustrations on use of equipment are based upon information contained in publication “Use and Care of Drawing Instruments,” by Eugene Dietzgen Co., with their permission.
    4
    FUNDAMENTALS OF MECHANICAL DRAWING	3-4
    the table or board, and with its top edge parallel to the upper edge of the T-square blade when the head of the T-square is held firmly against the left edge of the board. The corners of the paper are then fastened by means of an adhesive (masking or cellulose tape), care being exercised to have the paper smooth. Thumbtacks are occasionally used but are not as suitable as tape.
    4.	Pencils.—a. Drawing pencils are graded by letters from 6B (softest) through 5B, 4B, 3B, 2B, B, HB (medium soft), F, H (me-
    Figure 2.—Drawing board with T-square.
    dium hard), 2H. 3H, 4H, 5H, 6H, 7H, 8H, to 9H (extremely hard). Grades 4H and 6H are generally used for drawing lines while grades F, H, and 2H are preferred for lettering and sketching.
    b. The pencil is sharpened with a knife or pencil sharpener so that approximately % to % inch of the lead is exposed. A conical point of desired fineness may be obtained by rubbing back and forth on a sandpaper pad (fig. 3) rotating the pencil at the same time to avoid irregularly shaped sides on the point. The double bevel wedge point may be used for straight-line work. This type of point does not require sharpening as frequently as a conical point.
    c. When drawing lines, the pencil is held almost vertically (slightly tilted away from draftsman) with only a slight incline in the direction
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    4-6
    ARMY AIR FORCES
    of pencil movement. If the pencil has a conical point, frequent rotation will help preserve the sharpness of the point.
    5. Erasers.—a. A soft rubber eraser is required for erasing pencil lines, while a medium hard rubber eraser is best for erasing ink lines. A soft gum eraser is satisfactory for cleaning finished drawings.
    A When using an eraser, light, firm strokes should be made in one
    Figure 3.—Method of pointing pencil lead.
    Figure 4.—Use of erasing shield.
    direction only, keeping the paper taut with the thumb and second (middle) finger. An erasing shield (fig. 4) should be used whenever practicable to protect parts of the drawing which are not to be erased.
    6. T-square.—a. The T-square (fig. 5®) generally consists of a wooden blade with transparent celluloid edges, securely fastened at right angles to a head by means of screws.
    A The T-square is used for drawing horizontal lines and as a guide for drawing lines with triangles. When placed on the board (or table), the head of the T-square is held firmly against the left edge of
    6
    FUNDAMENTALS OF MECHANICAL DRAWING
    the board, and only the upper, or working edge, of the blade is used. The T-square is moved by sliding the head along the edge of the board with the left hand. After the working edge is located as desired, the left hand may be used to steady the blade. Left-handed draftsmen use the right side of the board and the right hand. If a drawing is removed from the board before it is completed and the work is again resumed, the drawing should be trued with the T-square and one of the lines of the drawing, not with the edge of the paper.
    /] \ 30° \
    y | CELLULOID EDGE----____________ 45°\
    d EAD	45°	3O°-6O°
    (D T-SQUARE	(2) TRIANGLES 7 * * * * * *
    ____________________________o___
    HORIZONTAL	VERTICAL	15°
    @ DRAWING LINES WITH T-SQUARE AND TRIANGLES Figure 5.—T-square, triangles, and their application.
    7. Triangles.—a. Triangles commonly used are of two types, the
    45° and the 30° to 60° (fig. 5®), and are usually made of transparent
    celluloid.
    b. Triangles, in combination with the T-square, are used in the con-
    struction of vertical and inclined lines. Figure 5® illustrates the
    common angles constructed with the use of triangles and the T-square.
    Arrows indicate the direction in which the lines are drawn.
    7
    7-9
    ARMY AIR FORCES
    c. Two triangles may be used to draw a line parallel to a given line AB, figure 6Q. Place a triangle in position so that one of its edges coincides with the line and place a second triangle against an edge of the first triangle. Hold the second triangle firmly in place, slide the first triangle to the desired position (fig. 6(2)), and draw the parallel line. A line perpendicular to the parallel lines could be drawn with the same position of the triangle, as shown in figure 6@. A T-square blade may be used in place of the second triangle.
    8. Irregular curve.—a. The irregular or “French” curve is used to draw a smooth curve which is not a true circle or an arc thereof. Points are first determined to locate the curve which is to be drawn, and the irregular curve fitted to match these points (fig. 7). When drawing the curve, successive sections are blended into one another to form a smooth continuous outline. A common procedure is to
    PARALLEL LINE	PERPENDICULAR LINES
    A	/ /	/AZ’-GIVEN LINE AB
    GIVEN LINEAB-v/ f
    GIVEN LINE A	/ ff
    /	triangle held/^^^^X^]	/
    / s'	FIRMLY	/// --------------
    2—_____________ / ——~1
    / ® 6 @ ®
    Figure 6.—Method for drawing parallel and perpendicular lines.
    carefully draw the curve, freehand and lightly, before accomplishment with the irregular curve.
    A Individual irregular curves of various shapes are available in sets. Individual curves are used in the same manner as the composite curve shown.
    9. Triangular scale.—a. The mechanical engineer’s or architect’s triangular scale (fig. 8®) is generally used in the preparation of mechanical drawings. The scale is intended only for measuring and should not be used as a straightedge. It has eleven sets of graduations or scales. At each end of the scales (except the full-size scale) is a number indicating the size of the main divisions on that scale. Numbers (upright) at the right end are read to the left, and those (upright) at the left end are read to right. When a scale on the left end is used, foot measurements are read to the right of the zero point and inch measurements are read to the left (fig. 8@). Conversely, when a scale on the right end is used, foot measurements are read to the left of the zero point and inch measurements to the right (fig. 8@).
    8
    FUNDAMENTALS OF MECHANICAL DRAWING
    9
    b. The full-size scale is used for drawings of the same size as the objects they describe. This scale (fig. 8(2)) is indicated by its number, 16, which denotes that it is divided into sixteenths of an inch. An object which is too large to be drawn to full-size scale is drawn to reduced scale. A reduced scale permits the use of smaller measuring units on
    Figure 7.—Use of irregular curve.
    the drawing; however, dimensions are never divided mathematically to reduced values but are always given full size. All reduced scales, except the %2- and %-inch scales, are divided into twelve or more parts on the inch side of the zero point, representing the 12 inches and fractions of inches of that scale foot. The %2- and %-inch scales have only six subdivisions on the inch side of the zero point, each subdivision representing 2 inches. Care should be exercised in reading the inch divisions in order to determine the correct inch unit or fractional
    9
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    ARMY AIR FORCES
    inch unit for the particular scale. Examples of scale reductions are as follows:
    (1)	The scale of 3 inches equals 1 foot, marked “3” (fig. 80), is used when the representation of the object is to be reduced so that 3 inches on the drawing is to be equivalent to 1 foot on the object. Accordingly, the 3 inches on the scale is divided into twelve 1-inch
    divisions; each inch division is further divided into eighths. The figure shows how 8% inches would be measured using this scale.
    (2)	The %-inch scale reduces 1 foot on the full-size object to % inch on the drawing. To reduce a dimension of 3 feet 7 inches to this scale (fig. 80), count three of the foot divisions to the right of the zero for the foot measurement, and seven of the inch divisions to the left of the zero for the inch measurement.
    10
    #	\	0 I 2	12 I
    ff'	0 2 V 9 9 01 29
    //	1*2 02 91 21 9 V 01
    hmlilMililihiy
    (T) TRIANGULAR SCALE
    0 I 2 3 In 3	6 9
    (2) FULL SCALE	(3) 3" SCALE
    i*  l0- _ j
    jrn 1111 h bwwwiW]
    8 I 0	2	4	1	6	C ,0	3 e 4	2 O 4 I
    @ t" SCALE	(5) 1" scale
    I*—9-2°——	I----e'-’i
    •	t	lM
    £ 0	4	8	12	16	20 J >	o	4
    @ SCALE	(7) SCALE
    Figure 8.—Mechanical engineer’s or architect’s triangular scale.
    FUNDAMENTALS OF MECHANICAL DRAWING	9-11
    (3)	The }4-inch scale reduces 1 foot on the full-size object to 14 inch on the drawing. To reduce a dimension of 4 feet 10 inches to Uiis scale (fig. 8@), count four of the foot divisions to the left of the zero, and ten of the inch divisions to the right of the zero.
    (4)	The %-inch scale reduces 1 foot on the full-size object to y8 inch on the drawing. To reduce a dimension of 9 feet 2 inches to this scale (fig. 8@), count nine of the foot divisions to the right of zero and one 2-inch division to the left (each division is 2 inches).
    (5)	The %-inch scale reduces 1 foot on the full-size object to % inch on the drawing. To reduce a dimension of 2 feet 7y2 inches to this scale (fig. 8©), count two of the foot divisions to the left of zero and seven and one-half of the inch divisions to the right.
    c. The civil engineer’s scale (not illustrated) consists of inches subdivided into tenths, twentieths, thirtieths, etc., and is adaptable for work on charts, maps, etc.
    10. Protractor.—The protractor (fig. 9) is used for setting off or measuring angles. The protractor illustrated is graduated from 0° to 180° in divisions of 1°. Protractors are also available with smaller divisions. The protractor is placed with its reference line over the line on the paper and its center mark or hole at the point on the line where the angle is to be drawn. The required angle may then be found on the outer edge of the protractor and the paper marked at this division. With protractor removed, a straight line is drawn through the point just found and the point with which the center of the protractor coincided, thus giving the required angle.
    11. Ruling pen.—The ruling pen (fig. 10©) consists of steel blades attached to a handle, and a thumbscrew for adjusting the distance between the points (nibs) of the blades to obtain the desired width of line. The ruling pen is used for inking straight lines and irregular curves. The pen is filled with ink (fig. 10@) by means of a quill which is fastened to the stopper of the drawing ink bottle. The height of the column of ink in the point should not exceed *4 inch. The pen should be held in a nearly vertical position against the straightedge with the nibs parallel to the edge (fig. 10@), and the handle inclined slightly in the direction of line. If the pen point is inclined toward the straightedge it will raise the inside nib, causing the ink to run under the straightedge and resulting in a blotted line. If the pen point is inclined away from the straightedge, it raises the outside nib, resulting in a ragged line. The pen is supported by the second finger with the straight blade adjacent to the straightedge, and held between the thumb and first (index) finger as shown in figure 10@.
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    ARMY AIR FORCES
    '	a°	90 'oo	/ '
    X. The compass is used with one hand. It may be opened with the second finger and thumb (fig. 13®) and set to the desired radius by placing the needle point at the center mark, adjusting the spread with the second and third fingers (fig. 13®). After the radius is set, the thumb and first finger are raised to the handle (fig. 13®). The compass is started at the near side of the circle to be drawn and revolved clockwise as shown in figure 13®, inclined slightly in the direction
    12
    FUNDAMENTALS OF MECHANICAL DRAWING
    13
    (T) RULING PEN
    (2) FILLING THE PEN	(3) CORRECT AND INCORRECT
    POINT POSITIONS
    @ CORRECT POSITIONS OF RULING PEN
    Figure 10,—Ruling pen and method of use.
    PAYZANT	CROW QUILL
    HOLDER
    SPEEDBALL
    STUB
    BALL
    Figure 11.—Lettering pens.
    (T) COMPASS
    (2) pen	(5) EXTENSION BAR
    Figure 12.—Compass and its parts.
    13
    13-14
    ARMY AIR FORCES
    of the line. To draw a circle with a radius of approximately iy2 inches, the pencil leg may be straight. For a larger circle, and always when using the pen leg, the legs of the compass should be adjusted perpendicular to the paper (fig. 14®). The extension bar is used to lengthen the pencil or pen leg of the compass to permit the drawing of large circles. Adjustment of the compass, using the extension bar, is shown in figure 14®. To avoid changing the radius, a circle is never drawn by holding the legs of the compass.
    /
    3
    Figure 13.—Use of compass.
    14« Dividers. This instrument is similar to the compass except that both legs are equipped with points (fig. 15®). It is used to transfer measurements on drawings, and for dividing a line into equal parts. Figure 15® shows the method of dividing a line into three equal parts by use of the dividers. The spread of the instrument is adjusted to approximately one-third the length of the line. This spread of distance is stepped off as shown by alternately swinging the divideis to either side of the line. If three of such distances do not
    14

    FUNDAMENTALS OF MECHANICAL DRAWING
    14-16
    equal the length of line, the setting of the dividers is increased or decreased (as the case may be) by one-third of the error. This trial and error method is continued until exact division is obtained.
    15. Bow instruments.—The use of the bow instruments (fig. 16(f)) is confined to small dimensions. For major adjustment of the bow instrument (fig. 16®), time is saved and wear of the threads avoided by holding the legs together while turning the adjusting
    Q WITH PEN
    (2) WITH EXTENSION BAR AND PEN
    Figure 14.—Adjustments with pen leg and extension bar.
    nut. After adjustment, the legs are gently released. A minor adjustment is made with the instrument in position and the point slightly raised as shown in figure 16®. After use, the instrument is opened to almost its full spread to release spring tension.
    16. Care of equipment.—Proper care will lengthen the service of equipment and promote neat and accurate work.
    a.	Each drawing instrument should be kept in its proper place in the instrument case when not in use. The drafting table should not be cluttered with idle instruments and tools.
    b.	A knife edge or abrasive should never be used to clean instruments. Such cleaning should be accomplished frequently with a soft cloth.
    15
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    ARMY AIR FORCES
    c.	Ink should not be permitted to dry in the nibs of the ruling pen or ink leg. Dried ink should be removed with a moistened cloth.
    d.	A lettering pen is not dipped into the ink; use the quill for the ruling pen (fig. 10). Frequently wipe the points on a soft cloth to prevent clogging. Clean the pen before putting it away, using warm water, and thoroughly dry it with a soft cloth. Never change the kind of ink on one point without first cleansing the point.
    e.	The joints of the compass and dividers should not be oiled.
    (?) DIVIDERS
    (D USING THE
    Figure 15.—Dividers
    DIVIDERS
    and their use.
    /. After considerable usage, pen nibs may become dull and worn. The nibs may be restored to their slightly rounded original shape by stroking them (screwed together) with a pendulum sweep on a fine Arkansas stone. The nibs are then separated and individually sharpened on the outside with sliding and rolling motion. The nibs should match perfectly and should not be beveled or scratched on the inside. When the pen is properly sharpened-it will draw the finest lines without leaving ragged edges or cutting the paper.
    g. Care should be exercised to avoid damage to triangle and T-square edges. Celluloid equipment may be cleaned with a little soap and cold water.
    h. Care should be exercised when a compass or dividers are adjusted on the scale, as the needle points may damage the surface of the scale.
    16
    FUNDAMENTALS OF MECHANICAL DRAWING
    17
    @ MAJOR ADJUSTMENT
    (3) MINOR ADJUSTMENT
    Figure 16.—Bow instruments and manner of adjustment.
    Section III
    LETTERING AND LINES
    Paragraph
    Lettering___________________________________________________...----------- 17
    Lines_____________________________________________________________________ 18
    17. Lettering.—Lettering, in addition to numerals, is employed on drawings to provide legible presentation of notes, dimensions, and other information. Single stroke (lines forming the letters being the width of one stroke of the pencil or pen) vertical and single stroke inclined letters are commonly used in mechanical drawings. These styles of lettering may be easily accomplished, and present a simple,
    513393°—43---2
    17
    DIVIDERS	PENCIL	PEN
    Q THREE TYPES
    17
    ARMY AIR FORCES
    balanced appearance. Vertical capitals are generally used in the title block, while vertical or inclined capitals, or capitals and lower-case letters, are used for notes.
    a. Vertical.—The proportions, method of accomplishment, and spacing of vertical letters (and numerals) are shown in figure 17.
    (1)	To insure accurate alinement, light guide lines-are drawm to limit the overall height of letters. Guide lines may be drawn with the T-square or with a guide-line triangle (fig. 18).
    [ A V fc H* 1 K L W T W X V W i
    [ T Z - F © J © G F V - C '$ ]
    L 0 Q
    2 3 4 5 6
    L 9 T 135917351 £88168164163
    s-S-AVIATION ^AVIATION 1
    [ 6W	i j ih 'i| m ; a line drawn through C and D will bisect the line AB.
    21.	Bisecting an arc.—Arc AB (fig. 25®) is given. With A and B as centers, and with a radius greater than half of arc AB, draw arcs that intersect at C and D. A line drawn through the points C and D bisects the arc AB.
    22.	Bisecting an angle.—Angle ABC (fig. 25®) is given. With B as a center, draw an arc cutting the sides of the angle at D and E. With D and E as centers, and with a radius greater than half of arc DE, draw arcs intersecting at F. A line drawn from B through the point F bisects the angle ABC.
    23.	Trisecting a right angle.—Right angle ABC (fig. 25®) is given. With B as a center, draw an arc cutting the sides of the angle
    24
    FUNDAMENTALS OF MECHANICAL DRAWING 23-27
    at D and E. With D and E as centers, and with the same radius, draw arcs intersecting arc DE at F and G. Lines drawn from B through points F and G trisect the angle ABC.
    24.	Erecting a perpendicular to a given line from a point outside the line.—Point P and line AB (fig. 26©) are given. With P as a center, and with a radius greater than the distance from P to AB, draw an arc cutting the line AB at C and D. With C and D as centers, and with a radius either greater or less than the distance from P to C or Z>, draw arcs intersecting at E or F. A line drawn through E and P or F and P will be perpendicular to the line AB.
    25.	Erecting a perpendicular to a given line from a point in the line.—Point P and line AB (fig. 26©) are given. With P as
    Figure 26.—Geometric constructions.
    a center, draw arcs cutting the line AB at C and D. With C and D as centers, and with a radius greater than half of CD, draw arcs intersecting at E. A line drawn through E to point P is perpendicular to the given line AB. If the point P is near the end of the line, .the line is extended and the same procedure followed.
    26.	Dividing a line into equal parts.—The given line AB (fig. 27©) is to be divided into seven equal parts. Starting at end B of the given line AB, mark off seven equal divisions at any convenient angle ABC to the given line. Connect the last mark G of the divisions and the opposite end of the given line A. Draw parallels to the line AC through each of the division marks, thus obtaining the equal divisions on the given line.
    27.	Drawing a circle through three points not in a straight line.—a. The three points A, B, and C (fig. 27©) are given. Join points A and B, and B and C. Erect perpendicular bisectors to AB and BC, intersecting at O. The radius of the required circle is OA, or OB, or OC.
    5. To find the center of a circle or arc, assume three points on the circle or arc and proceed as above.
    25
    28-30
    ARMY AIR FORCES
    28.	Constructing a square—Line AB (fig. 28®) is given. With 4 as a center, and with a radius R equal to AB, draw the arc EB. Erect a perpendicular at point A. With C and B as centers, and with a radius equal to AB, draw arcs intersecting and BD to complete the square.
    Figure 27.—Geometric constructions.
    at D. Draw CD
    1
    29.	Constructing a regular pentagon.—The circle (fig. 28®) with center 0 is given. Draw a diameter AB, and a radius OC perpendicular to it. Bisect OB, and with point D as a center, and with a radius DC, draw the arc CE. With C as a center, and with a radius CE, draw the arc EF. CF is one side of the pentagon. With the same radius, mark off the remaining three points and connect them.
    Figure 28.—Geometric constructions.
    30.	Constructing a regular hexagon.—a. The distance AB (fig. 29®) across corners is given. Draw a circle with AB as a diameter. With A and B as centers, and with a radius equal to one-half of AB, draw arcs cutting the circle at C, E, D, and F, and connect these points.
    b. The distance between parallel sides (fig- 29®) is given. Draw
    26
    FUNDAMENTALS OF MECHANICAL DRAWING
    30-33
    a circle having a diameter equal to the distance between the parallel sides. With the T-square and 30° to 60° triangle, draw lines tangent to the circle at A, B, C, D, E, and F.
    31. Constructing a regular octagon.—The square ABCD (fig. 29®) is given. Draw the diagonals of the square. With the cor-
    Figure 29.—Geometric constructions.
    ners as centers, and with a radius of half a diagonal, draw arcs cutting the sides of the square and connect these points.
    32. Drawing an arc tangent to two lines.—Two lines, AB and CD, and a radius R (fig. 30®) are given. Draw lines parallel to AB and CD at a distance R from them. The intersection of these lines will be the center of the required arc EF. Locate the points of
    Figure 30.—Geometric constructions.

    tangency by drawing lines through the center of the arc perpendicular to the tangent lines.
    33. Drawing an arc in a right angle.—The right angle ABC, and the radius R (fig. 30®) are given. With B as a center and with a radius R, draw an arc intersecting the sides at D and E. With D and E as centers, and with the same radius, draw arcs intersecting at O. With 0 as a center, and with the same radius, draw arc DE. This arc will be tangent to the lines AB and BC.
    27
    ® ® @
    34-35
    ARMY AIR FORCES
    34. Drawing an ellipse.—The major diameter AB and the minor diameter CD (fig. 31) are given. With the intersection (C) of these diameters as a center, draw circles on the major and minor diameters. Draw a number of radial lines OP, OQ, etc., cutting the large circle at P and Q and the small circle at P' and Q'. From P' and Q' draw lines parallel to the major diameter (AB), and from P and Q draw lines parallel to the minor axis (CD). The points of inter-
    / \ D / \
    A r-- --- -k-XX._—-1--JB
    \ / c \ /
    Figure 31.—Geometric constructions.
    section of these lines, H and H', are two points on the ellipse. Find as many points as necessary, and through them draw the curve.
    Section V
    ORTHOGRAPHIC PROJECTION
    Paragraph
    General_________________________________________________________________ 35
    Detailed description____________________________________________________ 3g
    Arrangement of views____________________________________________________ 37
    35. General.—a. The representation of an object as seen by an observer (pictorial view) is considered inadequate for shop use, because the true shapes of some surfaces are not revealed and dimensions are difficult to locate. These difficulties are overcome through the process of orthographic projection.
    b. Orthographic projection is the process of projecting accurate outlines of views of an object and properly arranging them. This method may best be explained through a process of tracing views of an object on the sides of a transparent box, and then manipulating the sides of the box (and consequently the traced views) in a mechanical method simulating the theory controlling the location and arrangement of the views necessary to present a picture of the object.
    28
    FUNDAMENTALS OF MECHANICAL DRAWING	36
    36. Detailed description.—a. (1) To obtain the front view of an object, imagine a transparent sheet, called the plane of projection (fig. 32®), located vertically in front of the object. By sighting perpendicularly through the plane of projection, the lines of sight will serve to guide the transfer of points of intersection, and lines representing the outline of the object, from the object to the plane of projection. Sighting at right angles, or perpendicularly, to the plane of projection
    xA X X	fl	pOB JECT	.	\\ T	X \
    FRONT PLANE OF PROJECTION “FRONT PLANE OF PROJECTION------------------------------------------' V*---------------SIDE PLANE OF PROJECTION
    (i) obtaining front view on plane of projection
    @ OBTAINING SIDE VIEW ON PLANE OF PROJECTION
    UNES OF SIGHT
    I I I II I I I
    1	I >0'4.1 ।
    I >0 11 iSs. i
    /T I I I I I I
    s'	I	I I I	I I I	I	j^ror PLANE or PROJECTION
    s'	I	I I 11 I I	I
    s'	।	X	ill	I
    s'''
    FRONT PLANE OF PROJECTION•x-'—SIDE PLANE OF PROJECTION
    @ OBTAINING TOP VIEW ON PLANE OF PROJECTION
    Figure 32.—Method of obtaining orthographic projection.
    is essential, as this is the factor which determines the accuracy of projection. Thus, the eye moves successively over the outline of the object to project the various points. As shown in figure 32, the line of sight originating at A passes through the plane of projection to meet the object at a. The point ax where the line of sight A intersects the plane of projection is the location of the projected point a. In like manner, the line of sight B will guide the projection of point b on the object to point br on the plane of projection. By repeating this operation at any number of points, the entire view may be transferred to the plane of projection. The projection thus obtained is an exact
    29
    36
    army air forces
    outline of the front view of the object, and may be clearly and accurately dimensioned.
    (2) To obtain a side view of the object, join a second plane of projection at right angles to the first plane as shown in figure 32®. Move
    the lines of sight to a position perpendicular to the second or side plane of projection. If the procedure outlined for the front plane of projection is now repeated for the side plane of projection, the result will be the orthographic projection of the right side of the object. Edges
    30
    / Top
    / T0P
    Z._------------------OBJECT
    ----I 2 J g	run	rq
    FRONT	--- I -I 1	I__I
    ---11	8,06---FRONT	(,	SI0E plane Or U----L—	-I		-	I	_______
    OJECTlON side plane of projection
    Q REVOLVING PROJECTION SURFACES INTO ONE PLANE	© PROJECTION SURFACES IN ONE PLANE
    5, 4. 3.
    TOT ia^=B	nn—■ n
    FRONT	[]	SIDE
    @ RELATION OF PROJECTIONS	© PROJECTION PLANES REMOVED
    Figure 33.—Revolving projection surfaces, and relation of views.
    FUNDAMENTALS OF MECHANICAL DRAWING 36-37
    and surfaces which are invisible in the plane of projection are indicated by the conventional symbol for hidden lines.
    (3) To obtain a top view of the object, join a third plane of projection horizontally above and at right angles to the front and side planes (fig. 32®). Move the lines of sight to a position perpendicular to the third or top plane. The lines of sight will now be parallel to the front and side planes. Repeat the procedure heretofore outlined to obtain the orthographic projection of the top of the object.
    b. If the side and top planes are imagined to be hinged to the front plane and are revolved away from the object (fig. 33®) until they coincide with the front plane, the three views appear on the same plane, of projection (fig. 33®). Figure 33® illustrates the relationship of the three views; in figure 33® the views are shown, as on a drawing, with the projection planes removed.
    c. Occasionally a cylindrical part may be shown in only one view (fig. 34) if the required diameters and other dimensions are all indicated
    Figure 34.—Single-view drawing.
    thereon. Some objects, such as a bushing (fig. 35), require only two views, as the side view duplicates the front view. In figure 36, the objects pictorially represented have front and top views which are similar, demonstrating the need of a third view for a complete understanding of the shape of the objects.
    37. Arrangement of views.—a. Frequently more than three views of an object are necessary. Figure 37 shows the relative positions of the six principal views of an object. A bottom view is used instead of a top view when the shapes or operations to be shown are on the under side of the part. For example, for an object such as a punch
    31
    37
    ARMY AIR FORCES
    and die, the arrangement of views would be as shown in figure 38. with the view of the bottom of the punch placed in the position of the bottom view, and the top of the die in the position of the top view. If space
    (duplicate of front view)
    Figure 35.—Two-view drawing.
    does permit, the bottom view may be placed to the right of the top view. The side view may also be placed across from the top view (fig. 39) when space does not permit location in the usual position.
    Z>. Views of an object on a plane not parallel to any of the usual views are called auxiliary views. When an object has an inclined
    32
    FUNDAMENTALS OF MECHANICAL DRAWING
    37
    surface, the true shape and size of such surface is not shown in any of the regular views, and an auxiliary view is necessary. This is especially true where the inclined surface is of irregular outline. Figure 40(1) shows a pictorial representation of a block with an inclined surface. The usual three views are shown at (2), and a front
    TOP	TOR
    PICTORIAL	PICTORIAL
    FRONT	SIDE	FRONT	SIDE
    TOP	TOP
    PICTORIAL	PICTORIAL
    FRONT	SIDE	FRONT	SIDE
    Figure 36.—Necessity of third view.
    and auxiliary view at @. In the regular orthographic projection, none of the three views shows the true outline of the inclined surface. With the front and auxiliary views, the inclined plane is shown with its true inclination and outline. For an understandable drawing of the object shown in figure 41(1), only a front view (2), a partial top view @, and a partial auxiliary view @ is required.
    513393°—43---3
    3-3
    37
    ARMY AIR FORCES
    PICTORIAL
    REPRESENTATION \JL /Z i
    «—--------------Ll_
    TOP
    /t7Ry\ ■■
    . ~T W” T-~ -W
    Mt3 ciTFJ	[Mr3--	—lJtJ-------<=4* 	—JK L
    --<¥—4—	=P=h i- rp	i[r.	njn
    tr ||F Hr
    REAR	LEFT SIDE	FRONT	RIGHT SIDE
    rn--------------m
    -_i	j Y~
    " -----------_
    -A r f p
    BOTTOM
    Figure 37.—Principal views of an object,
    fo
    P [~A~|	~2
    TOP VIEW OF DIE
    n-E-0—Q—i	n n
    U. 7”" J I 11
    |	H j)	tiTT
    । r D|E	J—।	r 1111 |
    FRONT	S|D£
    BOTTOM VIEW OF PUNCH
    Figure 38.—Choice of views.
    34
    FUNDAMENTALS OF MECHANICAL DRAWING
    37
    if
    ।	llil
    TOP	SIDE
    :	1=^
    front	usual position of side view
    Figure 89.—Arrangement of side view in limited space.
    PICTORIAL
    n—t—0
    top	/
    FRONT	SIDE	FRONT AND AUXILIARY VIEWS
    O	®
    Figure 40.—Front, top, side, and auxiliary views.
    35
    38
    ARMY AIR FORCES
    co lx
    ® yy ®
    p^y
    Figure 41.—Front, top, and auxiliary views.
    Section VI
    General_____________
    Perspective drawing. Isometric drawing.. Oblique drawing_____
    Cabinet drawing_____
    PICTORIAL DRAWING
    Paragraph
    38
    39
    40
    41
    42
    38. General. Pictorial drawings are seldom used by themselves as working drawings, but are generally used as illustrations where details of orthographic projection would not be easily understood. They have the advantage of requiring less training of the imagination to visualize a complicated object, and, in some instances, require less time to draw. Designers find it necessary and many workmen find it helpful to be able to present their ideas to others either with pictorial sketches or with one of the various styles of pictorial mechanical drawings. These drawings have the disadvantages of not always showing the true lengths or shapes of objects and of not showing hidden lines. In some types of pictorial drawing, a distorted appearance is given to the object drawn. A comparison of the types of pictorial drawings is shown in figure 42.
    36
    FUNDAMENTALS OF MECHANICAL DRAWING
    39
    39. Perspective drawing.—a. A perspective drawing represents an object on a plane surface as it appears to the eye, and affords a better pictorial effect than other types of drawings.
    PERSPECTIVE	ISOMETRIC
    OBLIQUE
    CABINET
    Figure 42.—Comparison of types of pictorial drawings.
    b. (1) One-point, or parallel perspective, drawings (fig. 43®) are those in which the object to be drawn is viewed in such a manner
    37
    VANISHING HORIZON	POINT
    ——————
    /V / /
    /' /
    ■ / / /
    ©
    ©
    Figure 43.—Perspective drawings.
    39-40
    ARMY AIR FORCES
    that one face is parallel to the front plane. In this style of perspective the horizontal lines of the front plane remain parallel, but the lines of all planes perpendicular to it meet at one point. The point at which the converging lines of a perspective drawing meet is called the vanishing point.
    (2) Two-point, or angular perspective, drawings (fig. 43©) are those in which the object to be drawn is viewed from an angle and in which the two sets of horizontal lines meet at respective points on the horizon.
    40. Isometric drawing.—a. If a cube is tilted so that its front view appears as shown in figure 44®, in which the edges AB, AC,
    Z	c	J>D
    C <	■>! D
    ^-FORESHORTENED
    6	^©Xactual length
    B
    © ISOMETRIC PROJECTION	@ ISOMETRIC DRAWING	® ISOMETRIC AXES
    'Z''
    30"\	.	30'
    ----------J—______________
    --B
    LAYOUT
    B
    COMPLETION
    © MAKING ISOMETRIC DRAWING
    Figure 44.—Isometric projection and drawing.
    and AD are equally foreshortened, an isometric projection is represented. An isometric drawing (fig. 44©) shows the cube in the same position with the actual length of edges shown. The isometric axes (fig. 44©) are the three lines of the front corner of the cube, and make angles of 120° with one another.
    b. In learning to make an isometric drawing it is best to start with some simple object such as a rectangular block. Lay off three light lines of indefinite length representing the isometric axes (fig. 44®).
    38
    FUNDAMENTALS OF MECHANICAL DRAWING
    40
    Mark off on the axes the length, breadth, and thickness of the block. The isometric drawing is then completed by drawing, through the points marked off, lines parallel to the isometric axes.
    c. (1) Invisible lines are not shown in isometric drawings unless they are necessary for the understanding of the drawing.
    (2)	A nonisometric line is one which is not parallel to any of the isometric axes and does not show its true length in an isometric drawing. To make an isometric drawing of an object having nonisometric lines, as line AC (fig. 45®), drop a perpendicular from C on the front
    E__________
    A C	D	(	s'	/\
    >	J
    B	/A
    C	D	| //	/	/ I s^
    s\------ ..	| s'	/	/ I s'
    /\	।
    A	F	B	\	A
    ®	(g)	®
    Figure 45.—Isometric drawing with nonisometric lines.
    view, giving the line CF. Draw the isometric axes AE and AB (fig. 45@) the same length as their corresponding length in the front and top views. Lay off AF on lines AB equal to its corresponding length on the front view. At F construct a vertical line FC equal to FC in the front view. Connect the points A and C which will give the nonisometric line AC in an isometric view (fig. 45®). The remaining lines are then drawn and the block completed.
    (3)	Angles in isometric drawings do not show in their true size, and therefore cannot be measured in degrees.
    (4)	Circles are drawn as ellipses in isometric drawings. Figure 46® shows a cube with an isometric circle drawn in each of its visible planes or faces. The first step in drawing an ellipse representing an isometric circle is to draw the isometric square ABCD (fig. 46®), having sides equal to the diameter of the circle desired. Perpendiculars are erected at F, F\ G, and 27, the midpoints of the four sides of the isometric square. These perpendiculars intersect at J and K. With A and 0 as centers, and with a radius equal to AH or CF, construct arcs HG and FF, respectively. With J and K as centers, and with a radius JH or FF, construct arcs EH and CF, respectively, thus completing the isometric circle. This method of constructing an ellipse is known as the four-center approximate method.
    39
    40
    ARMY AIR FORCES
    (5)	Isometric arcs (fig. 46@) are drawn as follows:
    («) The true radius is measured from the intersection of the two lines forming the sides of the isometric square, and perpendiculars are erected at the points thus located; the intersection of these perpendiculars gives the center of the required isometric arc.
    Figure 46.—Isometric circles, arcs, and curves.
    40
    €
    °\ ^-Xj / kK	> a
    V /	\V/\ i/\J^
    A
    Q	®

    At 0| Ct
    FUNDAMENTALS OF MECHANICAL DRAWING 40-42
    (&)	The radius of the isometric arc is the length of the perpendicular to the point of intersection.
    (6)	Isometric curves other than circles are drawn by first locating a number of points on an orthographic projection (fig. 46©). These points are then transferred to the isometric drawing (fig. 46©), and the curve drawn through these points.
    41.	Oblique drawing.—a. When an object is placed with one face parallel to the plane of projection and is projected by oblique lines to the plane, an oblique view results. This differs from orthographic and isometric projections in which the projectors are perpendicular to the plane of projection. The angle which the oblique lines make with the plane of projection is generally 45° (known as cavalier projection), although any angle less than 90° may be used. In an oblique drawing, one face or plane is shown without distortion. For that reason, any object to be drawn should be placed with its irregular outline in the front plane; if the object is of regular shape, the longest side should face the front plane.
    b. An oblique (fig. 47) is drawn on three axes similar to an isometric drawing except that one axis is drawn horizontally, one vertically, and one at an angle. Measurements are laid out along these axes representing the length, breadth, and thickness of the object, and the object completed as shown. Oblique circles (fig. 48) are drawn as true circles in the front plane and as approximate ellipses in the other planes by erecting perpendiculars at midpoint of the sides of the squares inclosing them.
    42.	Cabinet drawing.—Cabinet drawing is oblique drawing with all measurements on the oblique axis reduced one-half so as to overcome the distorted’ appearance of oblique drawing. Any angle may be used for the oblique axis of a cabinet drawing, but angles of 45° or 30° are generally preferred.
    41
    Figure 48.—Oblique circles.
    42	ARMY AIR FORCES
    Figure 47.—Oblique drawing.
    42
    FUNDAMENTALS OF MECHANICAL DRAWING	43
    Section VII
    SECTIONAL VIEWS AND THREADED PARTS
    Paragraph Sectional views_____________________________________________ 43
    Threaded parts____________________________________________ 44
    43.	Sectional views.—a. Frequently the usual views do not give a clear picture of the object. The difficulty generally lies with the invisible object lines, in which case a view into the interior of the object would help clarify the drawing. Such a view may be obtained by imaging enough of the exterior of the object removed to expose the internal construction. The type of section is determined by the amount of exterior removed.
    &. A sectional view (fig. 49) is obtained by imaging the object cut away, as if by sawing. The path of the saw is considered the cutting plane, that is, the plane upon which the cut is made. If one portion of the object is then removed and a drawing made of the remaining portion, the lines formerly invisible are exposed to view. Since sectioning an object is an imaginary operation, the other necessary views are not changed. The only addition is a cutting plane line, which traces the path of the cutting plane. A pictorial view of the object with the path of the cut traced by diagonal lines is shown in figure 49®. An orthographic projection with the side view sectioned is shown in figure 49®. The position of the cutting plane is located on the projected view by a cutting plane line. The view to be exposed after passing the cutting plane through the object is indicated by the direction of the arrows on the cutting plane line. When the cutting plane line coincides with the center line representing the symmetrical axis of the object, the cutting plane line may be omitted.
    c. Uniformly spaced, 45°, fine, parallel lines, termed cross hatching or section-lining, are used to distinguish surfaces of material theoretically cut and exposed by the cutting plane. The spacing of cross hatching varies from %2 to % inch, depending upon the size of the drawing and the part. The symbols used to designate various materials in sectional view (and in outside view) are shown in figure 50. The rules governing the use of symbols and related principles are as follows:
    (1)	Assembly drawings are cross hatched with the symbol representing the actual material of each part in the assembly. In figure 51 different materials are shown—cast iron, babbit, bronze, and steel.
    (2)	Detail drawings are cross hatched with the symbol for cast iron regardless of the material used; this practice simplifies the cross
    43
    43
    ARMY AIR FORCES
    hatching. The material of which the object is made is specified as a note on the drawing.
    (3)	Invisible object lines and details beyond the cutting plane are not shown on sectional views unless required for the necessary description of the object.
    (4)	When a cutting plane passes through a rib, web, or similar parallel element, the cross hatching is omitted from those parts (A-A, fig. 52).
    (5)	(a) When adjacent parts are shown in section (fig. 53®) the cross hatching is shown in opposite directions. Where a third part
    Figure 49.—Sectional view.
    is adjacent to two other parts, the angle of its cross hatching is made 30° or 60°.
    (&)	Where a part is sectioned in more than one place, the spacing and direction of the cross hatching is the same.
    (c) If 45° cross hatching would closely approach being parallel to one of the sides of the object, a different angle of cross hatching is used.
    (6) Parts such as bolts, nuts, rods, rivets, pins, keys, and shafts, the axes of which lie in the cutting plane, are not considered as cut lengthwise by the cutting plane, and therefore are not sectioned (fig. 53®). When the cutting plane passes at right angles to such parts, they are cross hatched as are other parts of the object.
    d. (1) A full sectional view (fig. 49) is obtained by passing a cutting plane across the entire object. In this operation, one-half of the object is considered removed; the other half, with the interior exposed to view, is drawn or projected in the manner of any other orthographic view.
    (a) X. sectional view need not be taken along a single, continuous cutting plane. The cutting plane may be turned or offset (A-A, B-B,
    44
    FUNDAMENTALS OF MECHANICAL DRAWING
    43
    SOUND OR HEAT INSULATION, CORK, HAIR-FELT, WOOL, ASBESTOS, MAGNESIA, PACKING, ETC.
    CONCRETE
    FLEXIBLE MATERIAL, FABRIC, FELT, RUBBER, LEATHER, ETC.
    BRICK AND STONE MASONRY
    ALUMINUM AND ALUMINUM ALLOYS
    WOOD{
    A-ACROSS GRAIN B-WITH GRAIN
    FIRE B RICK AND REFRACTORY MATERIAL
    ELECTRIC INSULATION, VULCANITE, FIBER,MICA, BAKELITE, ETC. SOLID FOR NARROW SECTIONS.
    ELECTRIC WINDI NGS, EL'ECTRO MAGNETS, RESISTANCE, ETC.
    BRONZE,BRASS, COPPER, AND COMPOSITIONS
    MARBLE,SLATE,GLASS,	ROCK
    PORCELAIN, ETC.
    WHITE METAL, Zl NC» LEAD,BABBITT ANO ALLOYS
    WATER AND OTHER	SAND
    LI QUIDS.
    (T) SECTION-LINING SYMBOLS
    TRANSPARENT MATERIAL, GLASS. CELLULOID,ETC.
    UNCOURSED AND COURSED RUBBLE
    ASHLAR	WOOD
    (2) OUTSIDE VIEW SYMBOLS
    Figure 50.—Symbols for materials.
    45
    STEEL
    CAST IRON
    43
    ARMY AIR FORCES
    fig. 52) to pass through other features to show the construction to better advantage. The cutting plane line is lettered at the points of change of direction.
    BRONZE—\	r—BABBITT
    CAST IRON—/	~ sy
    Figure 51.—Materials as shown on assembly drawing.
    --7	'^>A
    ----/Z/Xz
    SECTION B-B	//\ /
    //£;	^X\\
    ____/	J (/ X X \\\	\
    z	JU- --
    (g>
    \gZ
    SECTION A-A
    Figure 52.—Method of showing rib or web in sectional view.
    (6) When the true projection of a piece would be misleading, parts such as ribs or arms should be rotated until parallel to the plane of the section or projection (figs. 52 and 54). Similarly, holes in a flange in section (or elevation) are shown at their true distance from the center rather than in true projection (fig. 55).
    46
    FUNDAMENTALS OF MECHANICAL DRAWING
    43
    Figure 53.—Adjacent parts, bolts, nuts, shafts, etc., in sectional view.
    Figure 54.—Rotation into plane of section.
    Figure 55.—Holes in flange shown at true distance from center.
    47
    43
    ARMY AIR FORCES
    (2) A half-sectional view (fig. 56) may be drawn for a symmetrical object. This type of section is accomplished by passing two cutting planes at right angles to each other along the center lines or symmetrical axes. Thus one-quarter of the object is considered removed and the interior exposed to view. Invisible outlines are generally
    Figure 56.—Half-sectional view.
    A//	BREAK'sX
    ON VIEW-7 I	n/
    Figure 58.—Revolved section.
    omitted from the sectioned and unsectioned portions of the object but are shown in the unsectioned portion if the object is thus more clearly described. The half section provides a view which shows the internal and external features of an object.
    (3) A broken-out, or partial, section (fig. 57) is employed when it is desired to show only a portion of the object in sectional view. Frequently a broken-out section will eliminate the necessity of showing
    48
    Figure 57.—Broken-out section.
    FUNDAMENTALS OF MECHANICAL DRAWING 43-44
    a full or half-sectional view. The broken-out section is bounded at the break by a short break line.
    (4)	A revolved section (fig. 58) is used to show cross sections of arms, spokes of wheels, brackets, etc. The section is obtained by passing a cutting plane perpendicularly through the axis of the part and then revolving the sectioned portion one-quarter turn, showing the cross section on the longitudinal view. The revolved section may be shown directly on the view or in a break in the view.
    (5)	A detail section (B-B, fig. 52) is shown at some convenient location on the paper, entirely separate and removed from the regular projected view. The detail section is locate^ on the view by a cutting plane line. In order to clarify the construction of small details,
    Figure 59.—Phantom and thin sections.
    this type of section is frequently drawn to a larger scale than the view on which the section is indicated.
    (6)	A phantom section (fig. 59®) is indicated on an outside view by dashed cross hatching, and is used to show interior construction; the use of an additional view may occasionally thus be eliminated. Phantom sections are also used to indicate adjacent parts.
    (7)	Sections such as sheet metal, structural members, packing, gaskets, etc., which are too thin for cross hatching, may be shown solid on the sectional view (fig. 59@), with a space between thicknesses of such parts.
    44. Threaded parts.—a. (1) The use of screw thread representation on working drawings is extensive. The features of a screw thread are shown in figure 60. The relative terms (fig. 60®) may be defined as follows:
    (a) A screw thread is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder or cone.
    (Z>) The pitch is the distance from a point on a screw thread to a corresponding point on the next thread measured parallel to the axis.
    513393°—43-
    49
    44
    ARMY AIR FORCES
    () Regular internal thread symbols are shown in figure 65.
    7.	When the threads are tapped through, the representation is as shown in figure 65®.
    •2. When the point of the tap drill does not extend through the part, the representation is as in figure 65®.
    52
    FUNDAMENTALS OF MECHANICAL DRAWING	44
    3. The representation in figure 650 is employed to indicate a bottoming tap, when depth of thread is the same as depth of drill, or when it is not necessary to specify both depth of thread and depth of drill.
    (c) Simplified symbols for external and internal threads are shown, respectively, in figures 66 and 67. At a depth approximately equal to
    53
    |"-IONC~2 k________________________________	—i—
    -lllllllllll iiliillllll '	'< ? ■
    F------d y
    ©THREADS TAPPED THROUGH
    V— f’’-IONC-2
    EjyXXVNN	I	—H~~I
    X VlT" 1
    © TAP DRILL SHOWN
    f"-IONC-2 1"DEEP
    \\	V	!''	""’O
    A	Z\	i/	\ T>
    <\\v7\\yj RkXkXd	LXl—
    ©TAP DRILL NOT SHOWN
    Figure 65.—Regular symbols for internal threads.
    hat of the thread, hidden lines are drawn parallel to the axis to represent the threads. The simplified method of representation is not rec-nnmended for either exteriors or sectional views of assembled parts.
    (<7) Pipe threads are represented as shown in figure 68. The taper leed not be indicated but may be shown if desired.
    (e) An assembly of threaded parts is shown in figure 69.
    'y-J -10 NC -2-
    XXwj (- jX jj /Ox frOuQJ TO
    Figure 66.—Simplified symbols for external threads.
    44
    ARMY AIR FORCES
    Figure 69.—Assembly of threaded parts.
    54
    J-IONC-2
    Qthreads tapped through
    <— j-IONC-2
    (2)	TAP DRILL SHOWN
    ir-J-IONC-2 1*DEEP
    *	(3) TAP DRILL NOT SHOWN
    Figure 67.—Simplified symbols for internal threads.
    —	2" AM. STD. PIPE THREAD—-j	R—	2"AM. STD. PIPE THREAD -7
    . 7 I" AM. STD. PIPE THREAD?- VZZYNN)	X f '"AM- ST0‘ PIPE THRE7'’
    . .--------- -	< ////^	— - ———------------A
    l" AM. STD. PIPE TAP^^^^^	__ l" AM. STD, PI PE TAP
    REGULAR METHOD	SIMPLIFIED METHOD
    Figure 68.—Representation of American standard pipe thread.
    FUNDAMENTALS OF MECHANICAL DRAWING 45-46
    Section VIII
    SCALES. DIMENSIONS, AND NOTES
    Paragraph
    Scale of drawings_________________________________________________ 45
    Dimensions________________________________________________________ 46
    Notes___________________________________________________._________ 47
    45. Scale of drawings.—a. (1) Objects are drawn full size when the details thereof are clearly shown and the size of the paper will conveniently permit.
    (2) Enlarged drawings of views or sections are made when the actual size of the object is so small that full-size representation would not clearly present the features of the object.
    (3) Reduced-scale drawings are made of large objects that can be shown clearly in the smaller scale. The prime object in reducing the scale of drawings is to reduce the size of the drawing; therefore, as small a sheet is used as is practicable without crowding the views. The scale of drawings should not be reduced to such an extent that sectional views, notes, or tabulations cannot be added. Considerable clear space should always be left below the change block for the enlargement of this block.
    6. (1) The scale of a drawing is generally noted in the title block. When all views on a drawing are actual size the scale may be stated as “Full size”; in some practice, when the object is drawn full size the scale is not shown.
    (2)	When one or more views or sections are enlarged the notation “Enlarged view” or “Enlarged section,” as the case may be, is placed under the enlarged representation.
    (3)	(a) When all views are in the same reduced scale, the scale is noted in accordance with such reduction, as “One-half size,” or 6"=1'.
    (7)	When the main views are in one reduced scale and other views or sections are in another scale, each view or group of views has its own scale shown.
    46. Dimensions.—a. (1) Information as to the shape of the object is provided by the various views on the drawing. These shape representations must have dimensions applied to the various features to indicate the size of the object. Dimensions, as given, refer to the actual size of the object to be constructed, regardless of the scale to which the drawing is made.
    (2) A drawing must be so dimensioned that the parts shown thereon can be made without necessity of scaling the drawing. Dimensions should not be duplicated on various views or on a single view except
    55
    46
    ARMY AIR FORCES
    where they will add to the clarity of the drawing, and no more should be given than those required to produce the part. Dimensions of parts that can be measured or that can be produced with sufficient accuracy by using an ordinary scale should be written in units or common fractions. Parts requiring greater accuracy should be dimensioned in decimal fractions. Wire, tubing walls, sheet metal,
    r——	p-. p _ ..
    i i i i
    itr----------------------------t~r
    1	r+n	rS	I
    1--------Lp__________Ljj_______LlJ I ii| i! I—L
    ^—EXTENSION LINE
    I
    r-n~-----------------;---------TitfrH
    I pr-®---------------£---------I
    DIMENSION LINE
    Figure 70.—Dimension and extension lines.
    /- TAPER PIN
    X../- THRUST COLLAR
    IT fr
    ._____J.-t. /-SHAFT	_ _
    (	I I	STAMPING—\	V KNURL
    ----A--—T- i fiAX)
    UjJ ______________
    NECK"^
    Figure 71.—Method of placing leaders.
    standard metal bars and shapes, etc., should be described by the commercial designation followed by the dimension in decimals of an inch.
    (3) (a) Dimensions up to and including 72 inches are preferably expressed in inches, and those greater than this length in feet and inches.
    (S) In structural drawings, dimensions of 12 inches or over should be expressed in feet and inches.
    56
    FUNDAMENTALS OF MECHANICAL DRAWING
    46
    () Holes which are to be machined after coring or casting should have finish marks and finished dimensions specified. For counterbored holes the diameters and depths should be given, and for countersunk holes the angles and diameters should be given (fig. 78®).
    59
    46
    ARMY AIR FORCES
    (11)	Accurate dimensions which are to be established with limit gage or micrometer should be expressed in decimals to at least three places, and the drawing should give the limits between which the actual measurements must come (fig. 79). For external dimensions, the
    © ~
    W

    50°	5Qo
    70° 70°
    ' I \	I) 1
    60°	60°
    @
    Figure 76.—Dimensioning unlimited space and angles.
    maximum limit is placed above the line and for internal dimensions the minimum limit is placed above the line. This method should be used for smaller parts and where gages are extensively employed. A second method, used for larger parts and where few gages are emploved, is to give the calculated size to the required number of decimal places,
    60
    FUNDAMENTALS OF MECHANICAL DRAWING	46
    followed by the tolerances plus and minus, with the plus above the minus, as 8.625D _ _
    —----—drill
    -- I ziw \
    h- C-U 4
    (T)
    /S \	---j/T” J.R
    / I	' ZV ”7C8
    ©
    \ 1 / \
    ©
    _____I 111
    (4)
    Figure 77.—Dimensioning circles, arcs, and curves.
    (12) The difference in diameter or width in 1 foot of length is known as the “taper per foot.”
    (a) With standard tapers, give one diameter or width, the length,
    61
    46
    ARMY AIR FORCES
    and insert a note on the drawing designating the taper by number taken from American Standards.
    (&) With special tapers, when the slope is specified, the length and
    only one diameter should be given, or the diameters at both ends of the taper should be given and the length omitted (fig. 80).
    () Arcs may be accomplished by drawing tangent to the blocking lines (fig. 81®).
    66
    FUNDAMENTALS OF MECHANICAL DRAWING
    48
    c. (1) When executing an orthographic (or pictorial) sketch, the proportions of the object are judged by eye. The various features of the object may be advantageously compared for purpose of determining size.
    ().
    (2) (a) Assume that the cylinder (fig. 88@) is cut off at an angle (truncated). Draw the side and top views, and project a horizontal line AB, indefinite in length, from the bottom of the side view. Divide the top view into a number of equal angles. Set the dividers equal to the distance between the points where the sides of the angle cut the
    71
    50
    ARMY AIR FORCES
    circle, and step off on the horizontal line AB as many spaces as there are angles in the top view. From each division point on the horizontal line AB, draw ascending vertical measuring lines of indefinite
    ■* DlA.-t-»-	■<- DIA. X 3.1416 -►
    l
    -------L-i । । । । i i । । । i । । .. ©
    8/f	A12	V
    7/	\i Zz VZK /
    —-----*■-'------ z6	----------------Q-^=--------------------F
    —• -_________________________	|	23	BREAK SHARP 64	CORNERS
    *--------------------------------------- 2___________________________~
    k	J4	---------------H
    Note.—Limits on dimensions ±.0075 unless otherwise specified. Material—S. A. E. 1025 steel; F. A. O.—Smooth machine.
    Figure 102.—Detail of screw.
    86
    FUNDAMENTALS OF MECHANICAL DRAWING
    53
    BREAK SHARP CORNERS
    8.
    jO co
    _____ ________________________________________________ EM	BLY	1
    M42-27-1		BZ	.SE			1
    M42-27-2		JZ		SV	ZIVEL	1
    M 42-27-3		Gl	IIDE			1
    M 4-2-27-4		JZ	W			1
    M42-27-5		SC	REX	\/-R	ETAINING	1
    M42-28		S<	REX	V A	SSEN1BLY	1
    M42-28;l			5<	?RE	TV	1
    M42-28-2			Hz	XND	LE	1
    M42-28-3			C	ILL	AR	1

    Figure 105.—Part list.
    88
    INDEX
    Angle: Bisecting ___________________________________________________
    Trisecting______________________________________________
    Arc:
    Bisecting_______________________________________________
    Drawing_________________________________________________
    Arc tangent_________________________________________________
    Assembly and detail drawings________________________________
    Bisecting___________________________________________________
    Board, drawing______________________________________________
    Bow instruments_____________________________________________
    Cabinet drawing ____________________________________________
    Circle______________________________________________________
    Cloth ______________________________________________________
    Compass ____________________________________________________
    Curve, irregular--------------------------------------------
    Detail drawings_____________________________________________
    Development by triangulation-. _____________________________
    Dimensions__________________________________________________
    Dividers ___________________________________________________
    Drawing board_______________________________________________
    Ellipse_____________________________________________________
    Equipment and materials-------------------------------------
    Erasers-----------------------------------------------------
    Geometric constructions_____________________________________
    Hexagon_____________________________________________________
    Instruments, bow____________________________________________
    Irregular curve_____________________________________________
    Isometric drawing___________________________________________
    Lettering___________________________________________________
    Lines:
    Bisecting_______________________________________________
    Dividing, into equal parts______________________________
    Erecting perpendicular__________________________________
    Instructions and uses___________________________________
    Parallel, development___________________________________
    Radial, development_____________________________________
    Paragraph	Page
    22	24
    23	24
    21	24
    32,33	27
    32	27
    53	79
    20-22	24
    2	4
    15	15
    42	41
    27	25
    3	4
    3	4
    8	8
    53	79
    52	76
    46	55
    14	14
    2	4
    34	28
    2-16	4
    5	6
    19-34	23
    30	26
    15	15
    8	8
    40	38
    17	17
    20	24
    26	25
    24, 25	25
    18	20
    50	69
    51	73
    89
    IN DEX
    Paragraph Page
    Notes------------------------------------------------------- 47	63
    Oblique drawing_____________________________________________ 41	41
    Octagon____________________________________________________  31	27
    Orthographic projection__________________________________ 35-37	28
    Paper and cloth______________________________________________ 3	4
    Pencils______________________________________________________ 4	5
    Pens:
    Lettering_______________________________________________ 12	12
    Ruling 1________________________________________________ 11	11
    Pentagon____________________________________________________ 29	26
    Perpendicular, erecting------------------------------------- 24	25
    Perspective drawing_________________________________________ 39	37
    Pictorial drawing________________________________________ 38-42	36
    Protractor__________________________________________________ 10	11
    Representative working drawings_____________________________ 53	79
    Ruling pen__________________________________________________ 11	11
    Scale of drawings___________________________________________ 45	55
    Scale, triangular_____________,__________________________ 9	8
    Sectional views_____________________________________________ 43	43
    Sheet metal drafting_____________________________________ 49-52	68
    Sketching, technical________________________________________ 48	65
    Square, constructing_______________________________________  28	26
    Tangent, arc________________________________________________ 32	27
    Technical sketching______________________________________    48	65
    Triangles__________________________________________________   7	7
    Triangulation, development by_____________________________   52	76
    Triangular scale_____________________________________________ 9	8
    Treaded parts_______________________________________________ 44	49
    Trisecting a right angle____________________________________ 23	24
    T-square-------------------------------------------------     6	6
    [A. G. 062.11 (2-4-43).]
    By order of the Secretary of War :
    G. C. MARSHALL, Chief of Staff.
    Official :
    J. A. ULIO,
    Major General.
    The Adjutant General.
    Distribution :
    Band Hl (2).
    (For explanation of symbols see FM 21-6.)
    U. S. GOVERNMENT PRINTING OFFICE: 1943
    90
    Date Due
    A fine o	will be charged
    for each day the book is kept over time.
    		1
    	0>
    		1

    (Form 14)
    UNT LIBRARIES DENTON TX 76203 iiiiiiiiiiiiiiiiiin 1001728946