chapter 3 · chapter 3 sketching and ... usually orthographic multiview drawings,but they are...
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Chapter 3Sketching and Lettering
IntroductionHighly developed manual drafting skills are not required for the
preparation of CAD drawings (Fig. 3-1); however, a competent CADoperator must possess a thorough understanding of the principles ofdrafting and be skilled in technical sketching.
Observe how the sketch shown in Figure 3-2 is used to describethe object shown in Figure 3-3.This is another example of theproverb,“A picture is worth a thousand words.”
ObjectivesThe student will be able to:
• use proper line weightsto sketch and letter
• complete a two-dimensional sketch ofsimple objects
• complete a three-dimensional sketch ofsimple objects
• file a record of sketchedideas
• select and sharpensketching and letteringpencils
• keep sketches in proportion
• dimension a sketch
• shade a sketch
• letter clearly on a sketch
Figure 3-1 No manual drafting was required for this CAD-generated working drawing.(Courtesy of Caterpillar Inc.)
Chapter 3 – Sketching and Lettering
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SuppliesSketching supplies consist
of a wide variety of pencils,erasers, and drawing media. Softpencils in the range shown inFigure 3-4 are used for sketch-ing. Pencil points (Fig. 3-5) arerounded for sketching com-pared to the sharp points usedfor instrument drawing.However, sharp points on softpencils are used for layout andlettering guide line sketching.Chisel points are used for shad-ing. Sketching pencils aresharpened with amechanical sharpener, orwith a knife and file, orsandpaper to shape thepoint.
Although many typesof drawing media areused for technical sketch-ing, grid paper is themost practical and easy touse (Fig. 3-6). Grids pro-vide guide lines for rough scaling and proper alignmentof perpendicular and parallel lines. Use light-colored sur-faces if sketches are to be photocopied, and use translu-cent surfaces if diazo prints are to be made.Translucentsurfaces are alsohelpful if progressivedesign sketches areto be traced.
Figure 3-2A freehand sketch is worth a thousand words.
7B 6B 5B 4B 3B 2B B HB F H 2H 3H 4H 5H 6H 7H 8H 9H
Figure 3-4Recommended pencil grades for sketching
ROUNDED
OBJECT LINES
CHISEL
SHADING
POINTED
LAYOUT ANDGUIDE LINES
Figure 3-5Recommended pencil points for sketching
Figure 3-3An industrial product (Courtesy of Black and Decker U.S.Power Tools Group)
Figure 3-6Drawing on grid paper is faster andneater.(Photo by Ann Ross Wallach)
Fundamentals of Modern Drafting
Working Drawing SketchesWorking drawing sketches are used as the major design refer-
ence in manufacturing and construction. Sketches are also used asworking drawings when time and conditions preclude the prepara-tion of instrument or CAD working drawings.These sketches areusually orthographic multiview drawings, but they are sometimesprepared as pictorial drawings.An orthographic drawing shows sev-eral views of an object on a drawing surface that is perpendicular toboth the view and the lines of projection.A pictorial drawing showsan object’s depth; three sides of an object can be seen in one view.
OrthographicMultiviewSketches
Multiview sketchesprovide the greatestamount of detail for man-ufacturing and construc-tion. Figure 3-7 shows thesteps recommended tocomplete a multiviewsketch.As with instrumentdrawing (see Chapter 18), blocking in the overall outline beforecompleting the internal details is the key to maintaining correctscales, angles, and proportions.
Pictorial SketchesBlocking in the basic outline is also the
recommended procedure for pictorialsketches.There are three types of pictorialsketches: isometric, oblique, and perspective.
Isometric sketches are prepared byestablishing a vertical corner line and pro-jecting receding lines 30° (Fig. 3-8).As withmultiview sketches, always block in theentire outline of the object before cuttingcorners or adding surface details such asholes and projections.
Oblique sketches are pictorials thatrecede on only one side of an orthographicview. In preparing an oblique sketch, firstsketch a front view of the object (Fig. 3-9).Then extend lines from each corner upward at 45° or 30°. Connectthe ends of these lines with lines that are parallel to the lines of the
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Figure 3-7Steps to sketch a multiview drawing
Figure 3-8Steps to sketch an isometric drawing
Chapter 3 – Sketching and Lettering
front view. Oblique sketchesare easy to dimension sincethe width and length of thefront view are sketched toactual scale. Only the depthdimension is foreshortenedby the receding lines.
Perspective sketches arepictorials that contain reced-ing sides designed to approximate the actual appearance of an object.There are three types of perspectives: one-point, two-point, andthree-point.
1. One-point perspective sketches are similar to oblique draw-ings, except the receding lines do not follow a consistent angle.Receding lines are connected to a vanishing point. A vanish-ing point represents the point at which all receding lines appearto come together. It is similar to road or train tracks disappear-ing on the horizon. In sketching a one-point perspective, firstoutline the front view, as in oblique sketching. Establish a van-ishing point andsketch lines from eachcorner to this point(Fig. 3-10). Sketchlines representing theback of the objectparallel to the lines onthe front view.Thisblocks in the sketch.Now any angular cutsand details can beadded.
2. Two-point perspective sketches are similar to isometricsketches, except side lines recede to two vanishing points. Firstsketch the front vertical corner (Fig. 3-11). Establish two vanish-ing points above or below the front corner line, and connect thetop and bottom of the front corner line to each of these points.Vanishing points on two-point perspective sketches must alwaysbe located on ahorizontal linerepresentingthe horizon.Next, establishthe depth ofthe sides andconnect the
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Figure 3-9Steps to sketch an oblique drawing
Figure 3-10Steps to sketch a one-point perspective drawing
Figure 3-11Steps to sketch a two-point perspective drawing
Fundamentals of Modern Drafting
back corner lines also to the vanishing points. In two-point per-spectives, vertical lines are all parallel.
3. In three-point perspectives, vertical lines are projected to athird vanishing point that is aligned with the vertical front cor-ner line.Three-point perspectives are usually used for architec-tural pictorials, and rarely for technical drawings.
SketchingGuidelines and Procedures
Line conventions and letter-ing for technical sketches are simi-lar to those used for instrumentdrawings (Fig. 3-12). Sketchingstandards differ only in the degreeof line raggedness. Lines are darkand wide for object lines, dark andthin for dimension and centerlines, and thin and light for layoutand guide lines. Figure 3-13 shows the applicationof line conventions to a technical sketch.
All sketches are comprised of straight lines,circles and arcs, irregular curves, and letters andnumerals (Fig. 3-14). Sketches cannot be preparedwith the precision and accuracy of an instrumentor CAD drawing. Care must be taken to insurethat dimensions are relatively proportional. Ifdimensional proportions are grossly inaccurate,the sketch will misrepresent the actual appearanceof the object (Fig. 3-15).
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VISIBLE LINE
BORDER LINE
CUTTING PLANE
SHORT BREAK LINE
CENTERLINE
DIMENSION/EXTENSION LINES
SECTION LINE
HIDDEN LINE
LONG BREAK LINE
PHANTOM LINE
LEADER
GUIDE LINES/LAYOUT LINES (LIGHT)
Figure 3-12Line conventions for sketching working drawings
PHANTOM LINE
SECTION LINE
SHORT BREAK
GUIDE LINE
DIMENSION LINEEXTENSION LINE
CENTERLINEVISIBLE LINE
LONG BREAK
CUTTING PLANE
HIDDEN LINE
Figure 3-13Using line conventions on a working drawing
LINES
CIRCLES
CURVES
TEXT
Figure 3-14Four basic drawing forms make up alldrawings.
Chapter 3 – Sketching and Lettering
When sketchingstraight lines, squares, andrectangles, use shortstrokes. Do not attempt todraw continuous lines.Right-angle lines, unlesssketched on grid paper,should be laid out andsketched (Fig. 3-16).
Circles and arcs canbe accurately and sym-metrically sketched byfollowing the sequenceshown in Figure 3-17a.Just as the circle wasderived from the squarein Figure 3-17a, all filletsand rounds should first beblocked in square, as shown inFigure 3-17b. By followingthis procedure, proper propor-tions and symmetry can bemaintained.
The procedure andsequence for sketching ellipsesis similar to circle sketching(Fig. 3-18). Sketching accurateangles, other than right angles(90°), can be difficult withoutusing a triangle or protractor;however, by estimating anddividing a right angle intoeven angles, you can achievean acceptable level of accuracy(Fig. 3-19).
When sketching, hold thepencil comfortably (Fig. 3-20)and pull it (Fig. 3-21), neverpush it.To maintain a consis-tently rounded point andavoid wearing a flat chiselpoint, rotate the pencil fre-quently (Fig. 3-22).When eras-ing soft pencil sketches, use agood quality medium-softeraser.
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Figure 3-15Well-proportioned drawings havesuperior communication.
1 2
3 4
Figure 3-18Sketching ellipses
1 2 3 4
Figure 3-17aSketching circles
1
2
Figure 3-17bSketching fillets and rounds
1 2 3
Figure 3-16Sketching straight lines, squares, and rectangles
ShadingSurfaces exposed to a major
light source will appear bright.Conversely, surfaces not directlyexposed to a light source willbe shaded; therefore, addingshading to sketches creates real-ism (Fig. 3-23). In Figure 3-23,the light source is located aboveand to the left of the object.The opposite areas are shadedbecause direct light is blockedfrom these surfaces. Figure 3-24shows techniques for shadow-ing (shading) these areas.
Surfaces are rarely totallyhidden from a light source.Some surfaces are very light,very dark, or appear in a varietyof shadow grades depending onthe position, intensity, and num-ber of light sources. Figure 3-25shows an object with three lightlevels: light, medium, and dark.In addition, this figure shows aseparate shadow cast by theobject.
Fundamentals of Modern Drafting
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1 2
3 4
Figure 3-19Sketching and estimating angles
DRAW THEPENCIL
Figure 3-21Always pull the pencil—never push it.
Figure 3-22Rotate the pencil frequently forrounded points.
Figure 3-23Shade (darken) thesurfaces opposite the lightsource.
Figure 3-20Use a comfortable pencil grip for sketching.(Photo by Ann Ross Wallach)
Chapter 3 – Sketching and Lettering
Light travels in a straight line and cannot bendaround corners unless reflected; therefore, light intensityon surfaces always changes at the corners of objects.Figure 3-26 shows several methods of sketching these dif-ferences to add realism to a sketch. On objects withoutcorners, such as spheres and cylinders, light and dark areaschange gradually. Figure 3-27 shows several methods ofshadowing a cylinder sketch to add realism.
DimensioningWhen sketches are used for instruction, manufactur-
ing, or construction, dimensions are usually necessary toadequately describe the object.When sketches are dimen-sioned, the overall width, depth, and height dimensionsare placed on the outside of the location dimensions(Fig. 3-28).These are known as overall dimensions.Dimension lines are sketched parallel to object lines andconnected to the object with extension lines and arrows.Location dimensions show the location of parts of anobject. Size dimensions show the size of any hole orprojection on the object and are placed between theobject and the overall dimension lines. Dimensions areusually shown on multiview sketches. Pictorial sketches(Fig. 3-29) are normally used only to show the generalappearance of products and do not require dimensions.
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DARKSOLID
GRAYCLOSE LINES
LIGHT GRAYSPACED LINES
TEXTURE STIPPLE BLANKHIGH LIGHT
Figure 3-24Shading techniques
Figure 3-26Freehand shading of sharp corners
Figure 3-27Freehand shading of rounded surfaces
LIGHT SOURCE
Figure 3-25The light source dictates the positionof the shadows.
Fundamentals of Modern Drafting
LetteringSome information is best communicated with words or
numerals.Almost every sketch or drawing contains notes, labels,and dimensions that must be legible and consistent. In Figure 3-30, the title, material, and hole size are described with alettered notation. Each numeral used for dimensioning must bedistinct from all other numerals.The letter D which looks like anO, or the numeral 3, which looks like an 8, can be easily misreadand create costly manufacturing or construction mistakes. For thisreason, the American Society of Mechanical Engineers(ASME) style of letters and numerals (Fig. 3-31) is used by mostAmerican industries. Figure 3-32 shows the most efficient andquickest method of making these letters and numerals.A slantedform of this style (Fig. 3-33) is acceptable but is rarely used or rec-ommended for engineering drawings.
To letter most efficiently and legibly, always use guide lines(Fig. 3-34). Guide lines keep letters consistent and contained in thearea selected.As a general rule, most lettering is 1/8" high with 3/16" high title headings. Drawings to be microfilmed should be 3/16"or 1/4" high, using the microfont style shown in Figure 3-35.
Correct spacing between letters is also needed to produce letter-ing that is most readable. Figure 3-36 shows lettering that has the areabetween the letters approximately equal. By contrast, Figure 3-37shows wide and inconsistent spacing of letters. Notice how difficult it is to quickly read Figure 3-37 compared to Figure 3-36. Spacingbetween words and sentences is also important for effective reading.
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O
O
O
S
S
S
L
L
O = OVERALL DIMENSIONL = LOCATION DIMENSIONS = SIZE DIMENSION
Figure 3-28Types of dimensions
Figure 3-29Examples of pictorial sketches
Figure 3-30Working drawing sketch with dimensionsand notations
Figure 3-31Single-stroke vertical Gothic lettering (ASME standards)
Chapter 3 – Sketching and Lettering
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Figure 3-33Single-stroke slant (68°) Gothic lettering
Figure 3-34Guide lines will aid freehand lettering.
Figure 3-35Microfont lettering is recommended if drawing is to be microfilmed.
Figure 3-32Recommended lettering strokes
The space between wordsshould be approximately equalto the height of the letters.Thespace between sentences shouldbe twice the height of the letters (Fig. 3-38).
Fractions are among themost frequent causes of dimen-sional errors. If a numerator ordenominator is misread as awhole number, the result canbe disastrous. For this reason,the ASME spacing for fractions(Fig. 3-39) should be used toavoid confusion.
When all of the proceduresand guidelines for sketching arecombined, the result can be areadable and functional techni-cal sketch as shown at the leftin Figure 3-40. If these guide-lines are ignored, the confusingseries of lines and letters shownat right in Figure 3-40 canresult.
Fundamentals of Modern Drafting
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FUNDAMENTALS OF DRAFTINGWITH AUTOCAD
Figure 3-36The area between letters should be as equal aspossible.
TWICE HEIGHT OF LETTER
HEIGHT OF LETTER
THIS IS AN ENGINEERING TEXTFOR DRAFTING STUDENTS. ALLDIMENSIONS ARE IN INCHES.
Figure 3-38Spacing between words and sentences
Figure 3-39Fractions on the working drawing
Figure 3-40Which sketch gives better communication?
FU NDAM ENTAL S O F DRAF T IN GWI TH AU TOC A D
Figure 3-37Inconsistent areas between letters create reading difficulties.
Drafting Exercises
1. Sketch the isometric draw-ings in Figures 3-41through 3-47 on isometricgrid paper.
2. Sketch the multiviewdrawings in Figure 3-48.
3. Sketch the pickup truck inFigure 3-49.
4. Sketch the objects inFigure 3-50.
5. Sketch the tool-bit holderin Figure 3-51.
6. Practice lettering single-stroke Gothic lettering on1/8" grid paper.
7. Practice placing varioustypes of fonts in differentsizes and angular positionswith a CAD system.
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Figure 3-43
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Figure 3-44
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Figure 3-45
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Figure 3-46
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Figure 3-41
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Figure 3-42
Figure 3-47Isometric sketching practice
Figure 3-48Orthographic multiview sketching practice
Fundamentals of Modern Drafting
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Chapter 3 – Sketching and Lettering
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Figure 3-49Follow the steps to sketch the pickup.
Figure 3-50Sketching practice with real objects
4
2 HANDLE
SPRING
CHUCK
CHUCK COLLAR
2
3
3
4
1
Figure 3-51Sketch the tool-bit holder.
Fundamentals of Modern Drafting
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Chapter 3 – Sketching and Lettering
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1. Redesign and sketch the hexagon wrench in Figure 3-52.
3. Design a new tent stake asspecified in Figure 3-54.
4. Select one or more of theindustrial products inFigure 3-55 and sketch anew design.
Design Exercises2. Sketch the bookend in
Figure 3-53 and designyour stylized initials intothe surface.
Figure 3-52Redesign and sketch the hexagon wrench.
Figure 3-54
2X .5
2X .5
4.75
MAT’L .5" THK
WOOD BOOKEND
3.0
7.75
Figure 3-53Sketch the bookendwith your initials.
Fundamentals of Modern Drafting
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Figure 3-55Sketch a new design for one or more of these industrial products.
Key TermsAmerican Society of Mechanical
Engineers (ASME)Grid paperGuide linesIsometricLine conventionsLocation dimensions
MicrofontMultiviewObliqueOne-point perspectiveOrthographicOverall dimensionsPerspective
PictorialShadingSize dimensionsThree-point perspectiveTwo-point perspectiveVanishing pointWorking drawing
Tractor
Supersonic Rocket
Portable Radio
PowerHandsaw
Robot
Sports Car
Space Station
Clock RadioInk Pens
Desk Calculator Hand Calculator
Pencil Sharpener
Orbital HandsanderSewing Machine