Orthographic Projection Tutorial

8/16/2019 Orthographic Projection Tutorial

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ORTHOGRAPHIC PROJECTION

Most drawings produced and used in industry are multiview drawings. Multiview drawings are used to

provide accurate three-dimensional object information on two dimensional media, a means of

communicating all of the information necessary to transform an idea or concept into reality. The

standards and conventions of multiview drawings have been developed over many years, which equipus with a universally understood method of communication. Multiview drawings usually require several

orthographic projections to define the shape of a three-dimensional object. Each orthographic view is a

two-dimensional drawing showing only two of the three dimensions of the three-dimensional object.

Consequently, no individual view contains sufficient information to completely define the shape of the

three-dimensional object. All orthographic views must be looked at together to comprehend the shape

of the three-dimensional object. The arrangement and relationship between the views are therefore

very important in multiview drawings. Before taking a more in-depth look into the multiview drawings,

we will first look at the concepts and principles of projections.

BASIC PRINCIPLE OF PROJECTION

To better understand the theory of projection, one must become familiar with the elements that are

common to the principles of projection. First of all, the

1. Point Of Sight

The position of the observer in relation to the object and the plane of projection. It is from this point

that the view of the object is taken.

2. Plane of Projection

The observer views the features of the object through an imaginary PLANE OF PROJECTION (or IMAGEPLANE). Imagine yourself standing in front of a glass window, IMAGE PLANE, looking outward; the image

of a house at a distance is sketched on to the glass and is a 2D view of a 3D house.

3. Projection Lines

The lines connecting from the Point of Sight to the 3D object are called the Projection Lines or Lines of

Sight. Note that in the above figure, the projection lines are connected at the point of sight, and the

projected 2D image is smaller than the actual size of the 3D object.


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Now, if the projection lines are parallel to each other and the image plane is also perpendicular (normal)

to the projection lines, the result is what is known as an orthographic projection. When the projection

lines are parallel to each other, an accurate outline of the visible face of the object is obtained. The term

orthographic is derived from the word orthos meaning perpendicular or 90º.

PRINCIPLE VIEWS

To create the necessary 2D views, the point of sight is changed to project different views of the same

object; hence, each view is from a different point of sight. If the point of sight is moved to the front of

the object, this will result in the front view of the object. And then move the point of sight to the top of

the object and looking down at the top, and then move to the right side of the object, as the case may

be. Each additional view requires a new point of sight.


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MULTIVIEW ORTHOGRAPHIC PROJECTION

In creating multiview orthographic projection, different systems of projection can be used to create the

necessary views to fully describe the 3D object. In the figure below, two perpendicular planes are

established to form the image planes for a multiview orthographic projection. The angles formed

between the horizontal and the vertical planes are called the first, second, third, and fourth angles, as

indicated in the figure. For engineering drawings, both first angle projection and third angle projection

are commonly used.


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FIRST ANGLE PROJECTION

In first-angle projection, the object is placed in front of the image planes. And the views are formed by

projecting to the image plane located at the back.


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ROTATION OF THE HORIZONTAL AND PROFILE PLANES

In order to draw all three views of the object on the same plane, the horizontal (Top View) and profile

(Right Side view) are rotated into the same plane as the primary image plane (Front View).


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THIRD ANGLE PROJECTION

In third-angle projection, the image planes are placed in between the object and the observer. And the

views are formed by projecting to the image plane located in front of the object


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ROTATION OF THE HORIZONTAL AND PROFILE PLANES

In order to draw all three views of the object on the same plane, the horizontal (Top View) and profile

(Right Side view) are rotated into the same plane as the primary image plane (Front View)


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THE GLASS BOX AND THE SIX PRINCIPAL VIEWS

Considering the third angle projection described in the previous section further, we find that the object

can be entirely surrounded by a set of six planes, a Glass box. On these planes, views can be obtained of

the object as it is seen from the top, front, right side, left side, bottom, and rear.

Consider how the six sides of the glass box are being opened up into one plane. The front is the primary

plane, and the other sides are hinged and rotated into position.


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ALPHABET OF LINES

In technical Engineering drawings, each line has a definite meaning and is drawn in accordance to the

line conventions as illustrated in the figure below. Two widths of lines are typically used on drawings;

the thick line width should be 0.6 mm and the thin line width should be 0.3 mm.


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Visible Line

Visible lines are used to represent visible edges and boundaries. The line weight is thick, 0.6mm/0.024″).

Hidden Line

Hidden lines are used to represent edges and boundaries that are not visible from the viewing direction.The line weight is thin, 0.3mm/0.012″.

Center Line

Center lines are used to represent axes of symmetry. The line weight is thick, 0.3mm/0.012″.

Dimension Line, Extension Line and Leader

Dimension lines are used to show the sizes and locations of objects. The line weight is thick,

0.3mm/0.012″.

Cutting Plane Lines

Cutting Plane lines are used to represent the location of an imaginary cut has been made, so that the

interior of the object can be viewed. The line weight is thick, 0.6mm/0.024″. (Note that two forms of line

type can be used.)

Phantom Line

Phantom lines are used to represent imaginary features or objects, such as a rotated position of a part.

The line weight is thick, 0.3mm/0.012″.

Break Line

Break lines are used to represent imaginary cut, so that the interior of the object can be viewed. The line

weight is thick, 0.6mm/0.024″.


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PRECEDENCE OF LINES

In multiview drawings, coincidence lines may exist within the same view. For example, hidden features

may project lines to coincide with the visible object lines. And center lines may occur where there is a

visible or hidden outline. In creating a multiview drawing, the features of the design are to be

represented, therefore object and hidden lines take precedence over all other lines. And since the

visible outline is more important than hidden features, the visible object lines take precedence over

hidden lines. As shown in the below figure.

The following list gives the order of precedence of lines:

1. Visible object lines

2. Hidden lines

3. Center line or cutting plane line

4. Break lines

5. Dimension and extension lines

6. Crosshatch/section lines


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CREATING FIRST ANGLE ORTHOGRAPHIC PROJECTION

Now we will like to draw the orthographic projection of the isometric drawing in figure 1 below. We will

first try to draw the object in first angle orthographic projection.

Figure 1 – isometric view of an object

Creating a new document:

1. Click the Application Menu button and select New. The Select Template dialog box appears.

2. Choose Acadiso.dwt template to create a metric unit drawing.

3. Then Click the Open button

Figure 2 - The select template dialog box

Front

view


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Drawing setup:

1. Firstly, we want to set up the drawing limits. Type LIMITS and press ENTER to activate the drawing

limit command.

2. Specify the lower left corner by typing 0, 0 and then press ENTER.

3. Specify the upper right corner by typing 420, 297 and press ENTER. Now your drawing limit is set to

be at A3 size paper.

4. Press ESC to exit the drawing limits command

5. Double click the middle wheel of your mouse to zoom your drawing area to the drawing limit you

have set up in step 3.

6. Now we want to set up the drawing units. Click the Application Menu button and hover your mouse

on Drawing Utilities. Extra options comes out (see Figure 3).

Figure 3 – Drawing Utilities

7. Select Units and the Drawing Units dialog box opens.

8. Set the Length Type to Decimal, and the

precision to 0.00 from the list. Then, for the Angle

Type, set it to Decimal Degrees and the precision

to 0 from the list. Then set the Insertion scale to

Millimeters from the list.

9. Then press OK button. Now you drawing has

been set up to metric units drawing.


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Creating New Layers:

By default, in every new drawing, layer 0 will be created by AutoCAD automatically. This layer cannot be

deleted. For orthographic projections, several type of line will be use throughout the drawing. So we

want to create different layers for those lines so that our drawing is organized and systematic.

1. To set up the layers, go to Layer Panel under the Home Tab (see Figure 5).

Figure 5 – home tab and the layer panel

2. Click on the Layer Properties button . The Layer Properties Manager dialog box opens (see

Figure 6).

Figure 6–

the layer properties manager dialog box

3. Click on the New Layer button in the Layer Properties Manager dialog box or type Alt + N for the

shortcut to create new layer. Layer1 appears in the layer list (see Figure 7)

Figure 7 – The Layer1

4. Create six new layer with the following settings (see figure 8):


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Layer Color Linetype Lineweight

Object Green Continous 0.6mm

Foldlines Yellow Continous 0.6mm

Hidden Red Dashed line 0.3mm

Centre Red Centre line 0.3mm

Construction Grey Continous line 0.3mm

Dimension Purple Continous line 0.3mm

Figure 8 – The layer list

5. Highlight the Object Line layer in the list of layers

6. Click on Current Layer button to set the Object Layer as the current layer.

7. Click on the Close button to accept the settings and exit the Layer Properties Manager dialog box.

Drawing the front view:

1. Type LINE or Click the Line button in the Draw Panel to activate the line command.

2. Using relative coordinate method

a.

Specify the first point by typing

the origin value 0, 0

b.

Type @5, 0 and press ENTER

c.

Type @0, 1 and press ENTER d.

Type @-2, 0 and press ENTER

e.

Type @0, -0.5 and press ENTER

f.

Type @-2, 0 and press ENTER

g.

Type @0, 0.5 and press ENTER

h.

Type @1, 0 and press ENTER

i.

Type C and press ENTER

Figure 9 – Relative coordinate method

0, 0 5, 0

0, 1-2, 0

0, - 0.5-2, 0

0, 0.51, 0


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Creating foldlines:

1. Go to Layer Panel and Change the current layer

to Foldlines Layer from the dropdown menu list

(see Figure 10)

2. Click the Offset button or type O to

activate the offset command

3. Type 1 for the offset distance and presss ENTER

4. Offset line A and line B to the outer part of the

object (see Figure 10)

5. Connect the two lines you have created in step

4 using the Fillet command

6. Go to Layer Panel and change the lines above

to Foldlines Layer from the dropdown menu list

(see Figure 11)

7. To create the 45 degree foldline, left click the

verticle foldline and left click again the centre of

the foldline (see figure 12)

8. Press SPACEBAR twice and type Copy to copy

the line at an angle

9. Type 225 for the rotation angle and press

ENTER

10. To finish this command, press ESC. Now you

have the completed foldlines (see Figure 13)

Figure 10–

line A and Line B

Figure 11 – Layer dropdown menu

Figure 12–

center of the foldlines

Figure 13 – the complete foldlinesB

A


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Creating top view:

To create top view, you need construction

line to guide you.

1. In the Layer Panel, change the current

layer to Construction Layer from the

dropdown menu (see figure 14)

2. Left click the Object Snap icon to

activate the object snap properties

4. Right click the object snap icon and

activate the Endpoint option (see Figure 15)

5. To create construction line, type xline

and press ENTER

6. Specify a point on the object by left click

at an endpoint

7. Move your mouse vertically and click that

area to create vertical construction line.

8. Press ESC to finish the command

9. Click Offset button or type O and

press ENTER to activate the offset

command.

10. Type T and press ENTER to create offset

through.

11. Select the construction line, and offset it

to the next Endpoint.

12. Repeat step 9 to 11 to create

construction line as in the Figure 17.

13. Now, select all construction line and right click on screen.

14. Select Draw Order and select Send to

Back to change the drawing order of the

construction line to the back (see figure 18).

Figure 14 – construction layer

Figure 15 – Object Snap

Figure 16 – the construction line

Figure 17


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Figure 18 – Draw order

Now try to create the top view and the left view by using the step you have learn in this

tutorial. Don’t forget to show hidden line and center line!

Documents

Orthographic Projection Tutorial