7- Pictorial Projection

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Pictorial projection

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Introduction

¾ Pictorial drawing are type of technical illustration that show several faces of an object at once such as used in any industry design, sells,

manufacturing repair,

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¾

Axonometric and oblique pictorial drawing

are frequently used in technical

documents, sales literature, maintenance

manuals, and documentation supplements

in engineering drawing.

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¾

Perspective drawings use a converging

projection technique and more commonly

found in architectural drawings.

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Axonometric drawing

¾

The Greek word axon means axis and metric

means to measure.

¾

Axonometric projection is a parallel projection

technique used to create pictorial drawings of

objects by rotating the object on axis relative to a

projection plane to create a pictorial view.

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¾

Axonometric projection is one of four

principle projection techniques:

Multiview projection

Axonometric

Oblique

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¾

Axonometric projection is one of four

principle projection techniques:

Multiview

Axonometric projection

Oblique

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¾

Axonometric projection is one of four

principle projection techniques:

Multiview

Axonometric

Oblique projection

Perspective

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¾

Axonometric projection is one of four

principle projection techniques:

Multiview

Axonometric

Oblique

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Angles that determine the type of

axonometric drawing

¾ When all three angles are unequal the drawing is classified as a trimetric.

¾ When two of the three angles are equal the drawing is classified as a dimetric.

¾ When all three angles are equal the drawing is classified as a isometric.

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Although there are an infinite number of positions that can be used to create such a drawing only are few are used.

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Theory of isometric projection

¾

An isometric view of an object is created by rotating

it 45 degrees about a vertical axis.

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¾ Then the object tilted forward until the body diagonal of the cube (A-B) appears as a point in the front view.

¾ The angle the cube is titled forward is 35 degrees 16 minutes.

¾ The three corners meet to form equal angles of 120 degrees

¾ All the edges of the cube are

parallel to the edges that make up

the isometric axis since

projections of parallel lines are parallel.

¾ Any line that is parallel to one of the legs of the isometric axis is called an isometric line.

¾ The planes of the faces of the cube and all planes parallel to them are called isometric planes.

Theory of isometric projection

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The different scales of an isometric

projection and isometric drawing

¾ The forward tilt of the cube causes the edges and planes of the cube to become foreshortened as it is projected onto the picture plane. Thus the projected lengths are approximately 80% of the true lengths and an isometric projection ruler must be used.

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¾ If the drawing is drawn at full scale it is called an

isometric drawing. Isometric drawings are almost

always preferred over isometric projection for

engineering drawings, because they are easier to produce.

The different scales of an isometric

projection and isometric drawing (cont

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Position of isometric axes

¾

Isometric axes can be positioned in a number

of different ways to create different views of

the same object.

Regular isometric

looking down on the top of

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Position of isometric axes (cont

’

_’

d)

_d)

Reversed axis isometric

is developed by

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Position of isometric axes (cont

’

_’

d)

_d)

Long axis isometric

is developed by looking

from the right with one axis drawn at 60

degrees to the horizontal.

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Isometric lines vs.

nonisometric

_nonisometric

lines

_lines

¾

Any line that runs parallel to any of the isometric

axes is called an isometric line.

¾

Any line that does not run parallel to an isometric

axes is called a

non-isometric line.

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¾ Isometric planes are surfaces which are parallel to the

isometric surfaces formed by any two adjacent isometric axes.

¾ Planes which are not parallel to any isometric plane are called non-isometric planes.

Isometric planes vs.

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Standards for hidden lines on

isometric drawings

¾ In isometric drawings hidden lines are omitted unless absolutely necessary to completely describe the object.

¾ Normally, most isometric drawings will not have any hidden lines. You can avoid using hidden lines if the

most descriptive viewpoint is chosen.

However, there are times when the object has some features which

cannot be described no matter which isometric viewpoint is taken.

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¾ In isometric drawings center lines are drawn if symmetry

must be shown or for dimensioning.

¾ Normally, center lines are not used on isometric drawings when it not important.

Symmetrical part

Standards for center lines on

isometric drawings

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¾ Dimensioned isometric drawings used for production purposes must be ANSI standard, with dimension and extension lines and lines to be dimensioned lying in the same plane. Dimensioned drawings used for illustration purposes may use the aligned method.

Standards for dimensions on

isometric drawings

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The Boxing

-

In method for creating

Isometric Drawing

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Creating an isometric view of an

object with an oblique plane.

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To draw an angle

To draw an angle in an in an isometric drawing, locate the

isometric drawing, locate the

endpoints of the lines that form

the angle and draw the lines

between the endpoints.

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Irregular curves are drawn in isometric by constructing points along the curve in the multiview drawing which are then located in the isometric view. These points are then connected with an irregular curve drawing instrument.

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Representing circular features in an isometric

drawing

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Constructing a true

isometric ellipse.

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Creating an ellipse

using the four

-

center

method

Step 1: On the front plane, construct an isometric equilateral parallelogram whose sides are equal to the diameter of the circle

Step 2: Find the midpoint of each side of parallelogram.

Step 3: Draw two small arcs with radius r and center located at points A and B. Draw two large arcs with radius R, using the two corners C and D as the centers.

A

B C

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Drawing isometric ellipses using

an

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Construction

section lines

on the right side,

top, and front surfaces

Right view

Front view Top view

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Full-section isometric drawing

Half-section

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¾

¾ Isometric assembly drawingsIsometric assembly drawings used for production

purposes normally have circles, called balloons, that contain numbers and are attached to leader lines, point to the various parts.

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Dimetric

projection

¾ Dimetric projection is an axonometric representation in which two of the axes are at equal angles to the

plane of projection and two of the angles are equal and total more than 90 degrees.

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¾ It is worth noting that when laying out a dimetric drawing, the two equal axes can be laid out on either side of the vertical to create a symmetric dimetric projection. If one of the equal axes and the third axis are place on either side of the vertical, then an asymmetric dimetric

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TRIMETRIC PROJECTION

¾ Trimetric projection is the most realistic of the

axonometric projections, but is also the hardest to draw. In a trimetric projection, all three angles and scales are unequal.

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OBLIQUE

DRAWINGS

¾ Oblique drawings are a form of

pictorial drawings in which the most descriptive or natural front view is placed parallel to the plane of

projection.

¾ Oblique projection is used as the basis for both oblique drawing and oblique sketching.

¾ However, oblique projection and to a large extent oblique drawing, is not as commonly used as other types of

pictorials because of the excessive distortion that occurs. Because of its simplicity, many times oblique sketches

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¾ Oblique projection is a unique form of parallel projection. As the name indicates, oblique projection results when the projectors are parallel to each other but at some angle other than perpendicular to the projection plane.

¾ If the principal view of the object is placed such that its surfaces are parallel to the projection plane, the resulting projection is an oblique pictorial.

¾ Historically, the most descriptive face of an object in oblique projection has been placed parallel to the frontal plane

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¾ The cavalier oblique is drawn true length along the

receding axis.

¾ The cabinet oblique is drawn half the true length along the

receding axis.

¾ The general oblique can be drawn anywhere from full to

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The various angles for a cavalier

oblique drawing.

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¾ Any face of an object that is placed parallel to the frontal plane in oblique projection will be drawn true size and shape.

¾ Thus, the first rule in creating an oblique drawing is to develop

the drawing so that cylinders or irregular surfaces are placed parallel to the frontal plane. This allows these features to be