Pictorial Drawing 3s194n

Engineering Drawing (MEng 1001) Chapter Four Pictorial Drawing

Abdurazak Aman

Introduction • A pictorial drawing is a method of producing a three-dimensional object from a two-dimensional view, that shows the three main faces indicating the

height,

width

and

depth

simultaneously. It is an essential part of the graphic language.

Introduction Top Top View

H

Front View

W

H

Front Side View

D

W

Side

D

Comparison Between Multi-view and Pictorial Drawing Multi-view Drawing

Pictorial Drawing

It represents exact shape of an It represents overview of object. object.

an

It uses two or more views of an It represents several views of an object on different picture object at once on a single plane. picture plane. It uses hidden line to represent It rarely uses hidden line when the hidden parts of an object. necessary. It gives detail dimensions of a It gives overall dimensions of a complex object. complex object. It needs prior knowledge of It can be easily understood technical drawing to using common sense. understand. It is used for manufacturing, It is used for promotion, construction, production, and marketing and selling, business the like. transaction, and the like.

Types of Pictorial Projections Pictorial Projection

Axonometric

Oblique

Central/Perspec tive

Isometric

Cavalier

One Point

Dimetric

Cabinet

Two Point

Trimetric

General

Three Point

Types of Pictorial Projections • Axonometric projection is a projected view in which the lines of sight are perpendicular to the plane of projection, but the three faces of a rectangular object are all inclined to the plane of projection.

ISOMETRIC

DIMETRIC

TRIMETRIC

Types of Pictorial Projections • Isometric projection: The receding lines are drawn at 300 from the horizontal and the others are vertical. Consider a cubic object, the three principal faces and axes are equally inclined to the plane of projection.

Types of Pictorial Projections • Dimetric projection: Two of the principal faces and axes are equally inclined to the plane of projection.

Types of Pictorial Projections • Trimetric projection: All three principal faces and axes make different angles with the plane of projection.

Types of Pictorial Projections • Oblique projection: the projectors are oblique to the plane of projection but parallel to each other, and one of the principal face (usually front view) of the object is generally parallel to the plane of projection. The receding line is drawn at 300, 450 and 600 from the horizontal.

Types of Pictorial Projections • Cavalier: All lines of an object are drawn in their true length. True Length

45o

Types of Pictorial Projections • Cabinet: Lines on shortened by half.

the

receding

axis

Half Length

45 o

are

Types of Pictorial Projections • General: any oblique pictorial projection other than cavalier and cabinet. General Length

45o

Types of Pictorial Projections • Central/perspective projection is the most realistic three-dimensional view of all the pictorial projections, because it portrays the object in a manner that is most similar to how the human eye perceives the visual world. • Horizon: an imaginary horizontal line taken at eye level. • Vanishing point (VP): a point on the horizon where receding lines converge.

Types of Pictorial Projections • One point: have one vanishing point (VP). VP

Vanishes to one point

Types of Pictorial Projections • Two point: have two vanishing point. Vanishe s to one point

VP VP

Vanishe s to one point

Types of Pictorial Projections • Three point: have three vanishing point. Vanishe s to one point

VP

Vanishe s to one point

VP

VP

Vanishe s to one point

Isometric Drawings Difference Between Isometric Projection and Isometric Drawing: • An isometric projection is a true representation of the isometric view of an object. • An isometric drawing is an axonometric pictorial drawing for which the angle between each axes equals 120 0 and the scale used is full scale. • Isometric drawing is almost always preferred over isometric

projection

for

engineering

because it is easier to produce.

drawing,

Isometric Drawings Isometric projection (True projection)

Foreshorten ed (80% of true size)

Isometric drawing (Full scale)

Full scale

Isometric Drawings Isometric Axes: • Isometric axes are three lines that have common intersection points; the angle between each axis equals 120 0

. The plane made by two isometric

axes is called isometric plane.

Isometric Drawings

1 2

1st Position

2nd Position

Isometric Drawings Isometric and Non-Isometric Lines and Planes: • Isometric line is the line that run parallel to any of the isometric axes and includes normal line. • Any line that does not run parallel to any of isometric axes is called non-isometric line. And it includes inclined and oblique lines. • A plane that are not parallel to any isometric planes is called non-isometric plane. And it includes inclined and oblique planes. • Isometric Plane is the plane parallel to any of isometric planes and includes normal plane.

Isometric Drawings

Isometric Lines

Isometric Plane Non-Isometric Line

Non-Isometric Plane

Oblique Drawings Difference Between Oblique Projection and Oblique Drawing: • An oblique projection is a true representation of the oblique view of an object. • An oblique drawing is an pictorial drawing for which the angle between each vertical and horizontal axis is 90

0

and the angle between

horizontal and receding axis is usually 30 0, 45

0

and 60 0.

Oblique Drawings Oblique projection (True projection)

Oblique drawing (Full scale)

Oblique Drawings Oblique Axes: • Oblique

axes

are

three

namely,

vertical,

horizontal and receding axis; and the axes have common intersection points. The plane made by vertical and horizontal axis is called normal plane. The normal plane represents front view with true shape. • The advantage of oblique pictorials over isometric pictorials is that circular shapes parallel to normal plane are shown true shape and easy to sketch.

Oblique Drawings Vertical Axis

Receding Axis

Horizontal Axis

30, 45 and 60

Steps in Pictorial Drawing 1. Position the object. 2. Select isometric/oblique axis. 3. Sketch enclosing box. 4. Add details. 5. Darken visible lines.

Steps in Pictorial Drawing

Circles in Pictorial Drawing • Circles in pictorial drawing always become ellipses except it is parallel to normal plane of oblique pictorial. • In isometric drawing, the circle always become ellipse. • In oblique drawing when the circle is parallel to normal plane, it is drawn as its true shape and become circle; for other planes other than normal plane the circle becomes ellipse.

Circles in Pictorial Drawing

Circles in Pictorial Drawing Methods to Draw Ellipse: • There are two method namely, offset method and four center method. • The offset method can be diagonal approach and division approach.

Circles in Pictorial Drawing

Diagonal approach offset method.

Circles in Pictorial Drawing

Division approach offset method.

Circles in Pictorial Drawing • The four center method as its name indicates uses four center to draw an ellipse. It is efficient method. Steps in Four Center Method: 1. Draw a rhombus using the diameter of a circle. 2. Construct perpendicular bisecting lines from each side of rhombus. 3. Draw lines from obtuse angle corners to opposite side of rhombus by intersecting the midpoint. 4. Locate the four centers. 5. Draw the arcs with this centers and tangent to rhombus.

Circles in Pictorial Drawing

Four center method.

Arcs in Pictorial Drawing Arcs are usually sketched by locating their centers and then boxing in the enclosing rhombus and tangent to the rhombus.

Irregular Curves in Pictorial Drawing Steps: 1. Construct

points

along the curve in multi-view drawing. 2. Locate these points in

the

isometric

view. 3. Sketch connecting lines.

the

Inclined Surfaces in Pictorial Drawing x C x

B

A

B

x

x A y

C

y C

B

A

Non-isometric line

Hidden Lines in Pictorial Drawing • In pictorial drawings, hidden lines are omitted unless they are absolutely necessary to completely describe the object. Most pictorial drawings will not have hidden lines. • To avoid using hidden lines, choose the most descriptive viewpoint. However, if an pictorial viewpoint can not clearly depicts all the major features, hidden lines may be used.

Hidden Lines in Pictorial Drawing

Hidden Lines in Pictorial Drawing