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7/29/2019 Basics of Sketching
1/11
UNIT 7
59
PICTORIAL SKETCHING
Pictorial sketching is widely used in industry becausethis type of sketching is easy to read and under-stand, Figure 71. It is also a quick and easy meansof communicating technical ideas. Isometric sketch-ing, one of several types of pictorial drawing, is the
most frequently used. With the use of pictorial gridsheets and ellipse templates, pictorial drawings canbe sketched quickly and accurately.
Viewing Direction
The pictorial sketch may be drawn so the part is viewedfrom above (birds eye view), or from below (worms eyeview), Figure 72. The part features you wish to shownormally govern the viewing direction selected.
ISOMETRIC SKETCHING
All isometric sketches are started by constructingthe isometric axes, which includes a vertical line forheight and isometric lines to the left and right, at an
angle of 30 from the horizon, for width and depth.The three faces seen in the isometric view are thesame faces that would be seen in the normal ortho-graphic views: top, front, and side, as shown inFigure 73(A). Figure 73(B) shows the selection of
NOSE LANDING GEAR
PAYLOA
D
18MBA
Y60FT
FORWARD ENGINES
SPACE SHUTTLE ORBITER
SIDE HATCHUMBILICAL PANEL
LAUNCHUMBILICAL PANEL
ELEVONS
RUDDER/SPEEDBRAKE
STARTRACKERPANEL
ORBITALPROPULSION
AFT REACTIONCONTROL ENGINES
BODY FLAP
MAIN ENGINES (3)
MAIN LANDING GEAR
LENGTH: 122 FT
WINGSPAN: 78 FT
WEIGHT: 150,000 LBS
HEIGHT: 57 FT
FIGURE 71 Application of a pictorial sketch.
(A) BIRDS EYE VIEW
(B) WORMS EYE VIEW
FIGURE 72 Viewing direction.
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60 Interpreting Engineering Drawings
120
120
30 30
120
(A) ORTHOGRAPHIC VIEWS (B) ISOMETRIC AXIS (C) ISOMETRIC SKETCH
A
A A
AFRONT
FRONT
TOP
TOP
SIDE
SIDE
30
A
FIGURE 73 Isometric axes and projection
.25
.38
.38
.38
.50
.50
.38
.38
.25
.38
EXAMPLE A EXAMPLE B
.38
.38
.25
.25
FIGURE 74 Construction of nonisometric lines.
the front corner A and the construction of theisometric axes. Figure 73(C) shows the completedisometric view. All lines are drawn to their true
length, measured along the isometric axes, and hid-den lines are usually omitted.
Isometric Grid Sheets
This type of isometric sketching paper has evenlyspaced lines running in three directions. Two sets oflines are sloped in the direction of the isometricaxes. The third set of lines is vertical and passesthrough the intersection of the sloping lines, as inFigure 72. The most commonly used grids are the
inch, which is further subdivided into either 4 or 10equal grids, and the centimeter, which is furthersubdivided into 10 equal grids of 1 mm. No units ofmeasure are shown on these sheets; therefore thespaces could represent any convenient unit of size.
Inclined Surfaces
Many objects have inclined surfaces that are repre-sented by sloping lines in orthographic views. In iso-metric drawings, sloping surfaces appear asnonisometric lines. To create them, their endpoints,which are found on the ends of isometric lines, are
joined with a straight line. Figure 74 shows how toconstruct nonisometric lines.
Circles and Arcs
A circle on the three faces of an object drawn inisometric has the shape of an ellipse, as shown inFigure 75. Practically all circles and arcs shownon isometric sketches are made with the use of anisometric ellipse template. The template shown in
Figure 75 combines ellipses, scales, and angles.
Markings on the ellipse coincide with the centerlines of the holes, speeding up the drawing of cir-cles and arcs.
Basic Steps to Followfor Isometric Sketching
To save time and to make a more accurate andneater-looking sketch, use an isometric ellipse tem-plate for drawing arcs and circles and a straightedgefor drawing long lines.
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UNIT 7 61
CIRCLES TOUCH SQUARESAT MID-POINT OF EACH SIDE
POSITION OF ISOMETRIC ELLIPSE
TEMPLATE FOR DRAWING CIRCLES
AND ARCS ON THE TOP VIEW
POSITION OF ISOMETRIC ELLIPSE
TEMPLATE FOR DRAWING CIRCLES
AND ARCS ON THE SIDE VIEW
POSITION OF ISOMETRIC ELLIPSE
TEMPLATE FOR DRAWING CIRCLES
AND ARCS ON THE FRONT VIEW
TOP PLANE
FRONT PLANESIDE PLANE
FIGURE 75 Using the isometric ellipse template for drawing circles and arcs.
A commonly used technique for sketching is tosketch a boxhavingthemaximumheight, width, and
depth of the object, and then the parts of the box,which are not part of the object, are removed, leav-ing the parts that form the total object, Figure 76.
Step 1. Build a Frame. The frame (or box) is theoverall size of the part to be drawn. It is drawn withconstruction lines.
Step 2. Block in the Overall Sizes for Each De-tail. These subblocks or frames enclose each detail.They are drawn with construction lines.
Step 3. Add the Details. Lightly sketch the shapesof the details using construction lines. For circles,
draw squares equal to the size of the diameter. Alsosketch in the lines to represent the center lines ofthe circle.
Step 4. Darken the Lines. Using a soft lead pencil,darken in the visible object lines.
OBLIQUE SKETCHING
This method of pictorial drawing is based on theprocedure of placing the object with one face par-allel to the frontal plane and placing the other two
faces on oblique (or receding) planes, to left or right,top or bottom, at any convenient angle. The three
axes of projection are vertical, horizontal, and re-ceding. Figure 77 illustrates a cube drawn in typi-cal positions with the receding axes at 60, 45, and30. This form of projection has the advantage ofshowing one face of the object without distortion.The face with the greatest irregularity of outline orcontour, the face with the greatest number of circu-lar features, or the face with the longest dimensionfaces the front, Figure 78.
Two types of oblique projection are used exten-sively. In cavalier oblique, all lines are made to theirtrue length, measured on the axes of the projection.
In cabinet oblique, the lines on the receding axis areshortened by one-half their true length to compen-sate for distortion and to approximate more closelywhat the human eye would see. For this reason, andbecause of the simplicity of projection, cabinetoblique is a commonly used form of pictorial repre-sentation, especially when circles and arcs are to bedrawn. Figure 79 shows a comparison of cavalierand cabinet oblique. Note that hidden lines areomitted unless required for clarity. Most of thedrawing techniques for isometric projection apply tooblique projection.
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62 Interpreting Engineering Drawings
(B) BASIC SKETCHING STEPS
STEP 1
BUILD THE FRAME
STEP 2
BLOCK IN THE DETAILS
STEP 3
ADD THE DETAILS
STEP 4
DARKEN THE LINES
(A) THE PART
FIGURE 76 Basic steps to follow for isometric sketching.
30 45 4560 60 30
FIGURE 77 Typical positions of receding axes for oblique projection.
Oblique Grid Sheets
This type of sketching paper is similar to the two-dimensional sketching paper except that 45 lines,which pass through the intersecting horizontaland vertical lines, are added in either one or both
directions. The most commonly used grids are theinch, which is subdivided into smaller evenly spacedgrids, and the centimeter. As there are no unitsof measurements shown on these sheets, thespaces can represent any convenient unit of length,Figure 710.
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UNIT 7 63
NOT ACCEPTABLE
NOT ACCEPTABLE
ACCEPTABLE
ACCEPTABLE
ACCEPTABLE
PART B
PART A
FIGURE 78 Two general rules for oblique projection.
Inclined Surfaces
Angles that are parallel to the picture plane aredrawn as their true size. Other angles can be laid offby locating the ends of the inclined line.
A part with notched corners is shown in Figure711(A). An oblique drawing with the angles paral-lel to the picture plane is shown in Figure 711(B).In Figure 711(C) the angles are parallel to the pro-file plane. In each case, the angle is laid off by mea-surement parallel to the oblique axes, as shown bythe construction lines. Because the part, in eachcase, is drawn in cabinet oblique, the receding linesare shortened by one-half their true length.
Circles and Arcs
Whenever possible, the face of the object havingcircles or arcs should be selected as the front face,so that such circles or arcs can be easily drawn intheir true shape, Figure 712.
When circles or arcs must be drawn on one of theoblique faces, the following method is recommended.With reference to Figure 712(B):
Block off an oblique square with center linesequal to the diameter of the circle required.Blocking in the circle first also helps to getthe proper size and shape of the ellipse. If anellipse template is available, select an ellipsethat fits within the square and touches thesides of the square at its midpoints. Usingthick, dark lines (object lines), draw the
oblique circle (ellipse), Figure 712(C). If an ellipse template is not available, lightly
sketch an ellipse within this square with thecircumference of the ellipse making contactwith the square at its midpoints, Figure712(B).
Using object lines, darken the oblique circle,Figure 712(C).
Basic Steps to Follow for Oblique
Sketching (Figure 713)
Step 1. Build a Frame. The frame or box is theoverall size of the part to be drawn. It is drawn withlight, thin lines.
Step 2. Block in the Overall Size of Each Detail.These subblocks or frames enclose each detail. Forcircles, draw squares equal to the diameter size.
L
CAVALIER PROJECTION CABINET PROJECTION
LL2
FIGURE 79 Types of oblique projection.
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64 Interpreting Engineering Drawings
(A)
THE PART
(B) (C)
PART SHOWN IN CABINET OBLIQUE PROJECTION
(D)
AC
C
C
C
F F
FF
D D
D
D
EE
E
EB
A AA
B BB
FIGURE 711 Drawing inclined surfaces.
(A) ADDING OBLIQUE SQUARES
AND CENTER LINES WHERE
CIRCLES ARE REQUIRED
(C) COMPLETING THE OBLIQUE
CIRCLES
(B) LIGHTLY SKETCHING IN THE
SIZE AND LOCATION OF
OBLIQUE CIRCLES
OBLIQUE CIRCLES PASSTHROUGH THESE LINE
INTERSECTIONS
D FOR CAVALIER
FOR CABINET
D
D2
FIGURE 712 Sketching oblique circles.
Also sketch the center lines. They are drawn usinglight, thin lines.
Step 3. Add the Details. Lightly sketch the shapeof the details in each of their frames. These detailsare drawn using light, thin lines. If an oblique circle(ellipse) template is available, the arcs and circles aredrawn using thick, dark (visible object) lines.
Step 4. Darken the Lines. Use a soft lead pencil todarken the lines.
REFERENCES
ASME Y14.4M-1989 (R1999) Pictorial DrawingFIGURE 710 Oblique sketching paper.
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UNIT 7 65
INTERNET RESOURCES
Animated Worksheets. For information onisometric and perspective drawings, see:http://www.animatedworksheets.co.uk.
(B) BASIC SKETCHING STEPS
STEP 1
BUILD THE FRAME
STEP 2
BLOCK IN THE DETAILS
STEP 3
ADD THE DETAILS
STEP 4
DARKEN THE LINES
(A) THE PART
FIGURE 713 Basic steps to follow for oblique sketching.
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66 Interpreting Engineering Drawings
PICTORIAL SKETCHING OF PARTS HAVING FLAT
SURFACES USING DECIMAL-INCH DIMENSIONING
ASSIGNMENT:
STIRRUP
BIRDS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
WORMS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
BRACE
ON AN ISOMETRIC OR OBLIQUE GRID SHEET SKETCH
A PICTORIAL DRAWING OF ONE OF THE PARTS SHOWN.
DO NOT DIMENSION. ONE SQUARE ON THE GRAPH
PAPER REPRESENTS .50 IN.
A-23
5.00
.50 .50
1.50
.50
6.50
.50
2.50
6.00 4.00
.50
7.50
1.50
1.501.50
.50
.50
5.00
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UNIT 7 67
PICTORIAL SKETCHING OF PARTS HAVING FLAT
SURFACES USING METRIC DIMENSIONING
ASSIGNMENT:
RATCHET
TABLET
BIRDS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
WORMS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
ON AN ISOMETRIC OR OBLIQUE GRID SHEET SKETCH
A PICTORIAL DRAWING OF ONE OF THE PARTS SHOWN.
DO NOT DIMENSION. ONE SQUARE ON THE GRAPH
PAPER REPRESENTS 10 mm.
A-24M
20
20
20
20
15 25
35
75
35
140
35
60
90 60
20
25
15
15
814040
20
30
30
20
1030
10 15
60
METRIC
DIMENSIONS IN MILLIMETERS
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68 Interpreting Engineering Drawings
ASSIGNMENT:
ON AN ISOMETRIC OR OBLIQUE GRID SHEET SKETCH
A PICTORIAL DRAWING OF ONE OF THE PARTS SHOWN.
DO NOT DIMENSION. ONE SQUARE ON THE GRAPH
PAPER REPRESENTS .25 IN.
A-25
ROD SPACER
SWIVEL HANGER
2.50
1.00
2.50
.50
.50
.50
4X1.25
4X.75
R1.25
1.75
2.75
1.50
R1.00
R.75
R.75
1.00
2.00
.50
.50
1.00
PICTORIAL SKETCHING OF PARTS HAVING CIRCULAR
FEATURES USING DECIMAL-INCH DIMENSIONING
BIRDS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
WORMS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
1.00
.50
1.50
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UNIT 7 69
PICTORIAL SKETCHING OF PARTS HAVING
CIRCULAR FEATURES USING METRIC DIMENSIONING
ASSIGNMENT:
BEARING
BIRDS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
WORMS EYE VIEW
ISOMETRIC LAYOUT OBLIQUE LAYOUT
ON AN ISOMETRIC OR OBLIQUE GRID SHEET SKETCH
A PICTORIAL DRAWING OF ONE OF THE PARTS SHOWN.
DO NOT DIMENSION. ONE SQUARE ON THE GRAPH
PAPER REPRESENTS 10 mm.
A-26M
110
60
70 40
100
METRIC
DIMENSIONS IN MILLIMETERS
BEARING SUPPORT
200
2X 20
R30
100
100
80
20
140
20