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Chapter 5

Pictorial Sketching

ObjectivesBe able to explain the difference between an

axonometric projection and an oblique

projection.

Be able to explain the difference between an

isometric projection and an isometric

drawing/sketch.

Be able to create an isometric and oblique

sketches from an actual object and multiview

drawing.

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AxonometricAxonometric& ObliqueProjection

Axonometric Projection

B

Parallel & normalto picture plane

AB

CD

Lineof

sightA

B

CD

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Axonometric ProjectionType of axonometric drawing

a

1 Isometric All angles are equal

Axonometric axis

a

b c2. Dimetric Two angles are equal.

b c1. Isometric All angles are equal.

AB

CDA

B

D

Axonometric axis

b

a

c3. Trimetric None of angles are

equal.

C

Axonometric axis

Parallel & obliqueto picture plane

Oblique Projection

A

BC

D

Lineof

sight

A

D

C

B

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Oblique Projection

Oblique drawing angle

A

D

C

B

BA

30o45o 60o

Type of Oblique drawing

1) Cavalier 2) CabinetC D

45o 45o

1) Cavalier 2) Cabinet

Fullscale Half

scale

Isometric ProjectionIsometric Projection& Isometric drawing

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Rotate 45about vertical axis

Isometric Projection

Tilt forward (35o16’)

All edges foreshortenabout 0.8 time.

Isometric DrawingIsometric drawing is a drawing drawn on an isometric

axes using full scale.

Isometric projection(True projection)

Isometric drawing(Full scale)

Forshorten

Full scale

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Positions of Isometric AxesIsometric axes can be arbitrarily positioned to create

different views of a single object.

Regularisometric

Reverse axisisometric

Long axisisometric

View point is lookingdown on the top ofthe object.

View point is lookingup on the bottom ofthe object.

View point is lookingfrom the right (or left)of the object.

Distance in Isometric DrawingTrue-length distances are shown along

isometric lines.

Isometric line is the line that run parallel to

any of the isometric axes.

Nonisometric lines

Isometric axes

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IsometricIsometricSketching

1. Place the object in the position which its shape

and features are clearly seen

Sketch from an actual object

2. Define an isometric axis.

3. Sketching the enclosing box.

4. Estimate the size an and relationship of each

and features are clearly seen.

details.

5. Darken all visible lines.

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STEPS

Sketch from an actual object

1. Positioning object.

2. Select isometric axis.

3. Sketch enclosing box.

4. Add details.

5. Darken visible lines.

1. Positioning object.

Sketch from an actual objectSTEPS

2. Select isometric axis.

3. Sketch enclosingbox.

4. Add details.

5 Darken visible lines

Note In isometric sketch/drawing), hidden lines are omitted

unless they are absolutely necessary to completely

describe the object.

5. Darken visible lines.

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1. Interprete the meaning of lines/areas in

Sketch from multiview drawing

multiview drawing.

2. Locate the lines or surfaces relative to isometric

axis.

Top View

Example 1 : Object has only normal surfaces

Front

Top

Regular H

Front View Side View

Side

WD

H

DW

Bottom View

Bottom

FrontSide

Reverse

DW

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Example 2 : Object has inclined surfaces

DH

y

y

x

Nonisometric line

W

x Front View

A x

x

BC

Example 3 : Object has inclined surfaces

A

y

xB

C

x

y

Nonisometric line

ABC

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x

y

Regular

C

Example 4

A

B

B

C D

E

D FFront View

Reverse

A EF

Circle & Arc in IsometricIn isometric drawing, a circle appears as an ellipse.

Sketching Steps

2. Construct an isometric square.

3. Sketch arcs that connect the

tangent points.

Sketching Steps

1. Locate the center of an ellipse.

tangent points.

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Circle & Arc in IsometricFour-center method is usually used when drawn an

isometric ellipse with drawing instrument.

3. Construct a perpendicular

bisector from each tangent point

Sketching Steps

2. Construct an isometric square.

1. Locate the center of an ellipse.

bisector from each tangent point.

4. Locate the four centers.

5. Draw the arcs with these centers

and tangent to isometric square.

Example 5

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Irregular Curve in Isometric

1 Construct points along the

Steps

1. Construct points along the

curve in multiview drawing.

2. Locate these points in the

isometric view.

3 Sketch the connecting lines3. Sketch the connecting lines.

ObliqueObliqueSketching

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Object Orientation Guidelines

Place complex features (arc, hole, irregular shapesurface parallel to frontal plane.

Object Orientation GuidelinesThe longest dimension of an object should beparallel to the frontal plane.

GOOD GOOD

WORSE WORSE

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Object Orientation Guidelines

Which orientation is better ?

Sketch from actual object

D

ESTIMATE DEPTHESTIMATE LINES

45

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Sketch from multiview drawing

Sketch from multiview drawing

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Sketch from multiview drawing

B

C

D

E

AB

Sketch from multiview drawing

B

C

D

E

AB

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Sketch from multiview drawing

B

D

E

C

AB

Sketch from multiview drawing

B

D

E

C

AB