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Orthographic ProjectionPart-1

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PROJECTION METHOD

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Line of sight is an imaginary ray of light between an

observer’s eye and an object.

Line of sight

Parallel projection

Line of sight

Perspective projection

There are 2 types of LOS : parallel convergeand

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Plane of projection is an imaginary flat plane which

the image is created.

The image is produced by connecting the points where

the LOS pierce the projection plane.

Parallel projection Perspective projection

Plane of projection Plane of projection

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Disadvantage ofPerspective Projection

Perspective projection is not

used by engineer for manu-

facturing of parts, because

1) It is difficult to create.

2) It does not reveal exact

shape and size.Width is distorted

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Orthographic Projection

Orthographic Projection

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5

Orthographic projection is a parallel projection technique

in which the parallel lines of sight are perpendicular to the

projection plane

MEANING

Object views from top

Projection plane

1

2

3

4

51 2 3 4

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Orthographic projection technique can produce either

1. Multiview drawing that each view show an object in two dimensions.

2. Axonometric drawing that show all three dimensions of an object in one view.

Both drawing types are used in technical drawing for

communication.

NOTES

ORTHOGRAPHIC VIEW

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Axonometric (Isometric) Drawing

Easy to understand

Right angle becomes obtuse angle.

Circular hole becomes ellipse.

Distortions of shape and size in isometric drawing

Advantage

Disadvantage Shape and angle distortion

Example

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Multiview Drawing

It represents accurate shape and size.Advantage

Disadvantage Require practice in writing and reading.

Multiviews drawing (2-view drawing)Example

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ORTHOGRAPHIC PROJECTIONS:

Horizontal Plane (HP), Vertical Frontal Plane ( VP )

Side Or Profile Plane ( PP)

Different Reference planes are

FV is a view projected on VP.TV is a view projected on HP.SV is a view projected on PP.

And

Different Views are Front View (FV), Top View (TV) and Side View (SV)

IT IS A TECHNICAL DRAWING IN WHICH DIFFERENT VIEWS OF AN OBJECT ARE PROJECTED ON DIFFERENT REFERENCE PLANES

OBSERVING PERPENDICULAR TO RESPECTIVE REFERENCE PLANE

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Orthographic Projections are a collection of 2-D drawings that work together to give an accurate overall representation of an object.

Defining the Six Principal Views or

Orthographic Views

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A.I.P. to Vp & to Hp

A.V.P. to Hp & to Vp

PLANES

PRINCIPAL PLANESHP AND VP

AUXILIARY PLANES

Auxiliary Vertical Plane(A.V.P.)

Profile Plane ( P.P.)

Auxiliary Inclined Plane(A.I.P.)

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Object

PICTUREPLANE

Observer

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Glass Box Approach

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Glass Box Approach

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Glass Box Approach

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Glass Box Approach

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Glass Box Approach

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Glass Box Approach

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Third-angle Projection

First-angle Projection

First and Third Angle Projections

• First Angle• Third Angle

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Conventional Orthographic Views

Height

Depth

Width

Front View

Top View/Plan

Right Side View

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Lines on an engineering drawing signify more than just the geometry of the object and it isimportant that the appropriate line type is used.

Line Thickness

For most engineering drawings you will require two thickness', a thick and thin line. The general recommendation are that thick lines are twice as thick as thin lines.

                                             A thick continuous line is used for visible edges and outlines.

                                             

A thin line is used for hatching, leader lines, short centre lines, dimensions and projections.

Line Styles

Other line styles used to clarify important features on drawings are:

                                             Thin chain lines are a common feature on engineering drawings used to indicate centre lines. Centre lines are used to identify the centre of a circle, cylindrical features, or a line of symmetry.

                                              Dashed lines are used to show important hidden detail for example wall thickness and holes..

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• Visible lines takes precedence over all other lines

• Hidden lines and cutting plane lines take precedence over center lines

• Center lines have lowest precedence

Precedence of Lines

0.6 mm

0.3 mm

0.6 mm

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For Example:

1. Visible2. Hidden3. Center

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Dimensioning

A dimensioned drawing should provide all the information necessary for a finished product or part to be manufactured. An example dimension is shown below.

Dimensions are always drawn using continuous thin lines. Two projection lines indicate where the dimension starts and finishes. Projection lines do not touch the object and are drawn perpendicular to the element you are dimensioning.All dimensions less than 1 should have a leading zero. i.e. .35 should be written as 0.35

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Types of Dimensioning

• Parallel Dimensioning• Parallel dimensioning consists of several

dimensions originating from one projection line.

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•Superimposed Running Dimensions

•Superimposed running dimensioning simplifies parallel dimensions in order to reduce the space used on a drawing. The common origin for the dimension lines is indicated by a small circle at the intersection of the first dimension and the projection

line.

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•Chain Dimensioning

•Combined DimensionsA combined dimension uses both chain and parallel dimensioning.

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Dimensioning of circles

• (a) shows two common methods of dimensioning a circle. One method dimensions the circle between two lines projected from two diametrically opposite points. The second method dimensions the circle internally.

• (b) is used when the circle is too small for the dimension to be easily read if it was placed inside the circle.

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Dimensioning Radii

• All radial dimensions are proceeded by the capital R.

(a) shows a radius dimensioned with the centre of the radius located on the drawing.

(b) shows how to dimension radii which do not need their centres locating.

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Tolerancing

• It is not possible in practice to manufacture products to the exact figures displayed on an engineering drawing. The accuracy depends largely on the manufacturing process. A tolerance value shows the manufacturing department the maximum permissible variation from the dimension.

• Each dimension on a drawing must include a tolerance value. This can appear either as:

• a general tolerance value applicable to several dimensions. i.e. a note specifying that the General Tolerance +/- 0.5 mm.

• or a tolerance specific to that dimension

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Unidirectional Systemvalues read from bottom only(Preferred when?)

Aligned Systemvalues read from bottom and Right side

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CORRECTINCORRECT

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Dimensioning a circular arc.

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Omit unnecessary dimensions.

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Use of enlarged view to clarify dimensions.

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