3rd angle orthogonal

theory topics

 

On this page are the steps for you to learn about and complete an Orthogonal Drawing to approved Australian Standards. (AS 1100)

  1. Model Answer
  2. What is a 3rd Angle Orthogonal drawing?
  3. Who uses them? What are they for?
    • Rules for Orthogonal drawings
  4. Setting out an orthogonal drawing
  5. Lines in Australian Standards
  6. Drawing an Orthogonal drawing
  7. Application of Australian Standards
  8. Sectional drawings

Back to top

 

1 Model answer

 

Here is an example of a manual drawing from a Year 11 student. It shows correct set out, labels, dimensions, title box and 3rd Angle Orthogonal symbol.

 

manually drawn 3rd angle orthogonal

 

mariana
Here is a hand drawn 3rd Angle Orthogonal by student Mariana Velo.

 

 

Back to top

 

 

2 What is a 3rd Angle Orthogonal drawing?

 

 

watch this animation of the 3rd angle space

 

Watch as three views of a church are projected onto glass then flatened out into a completed 3rd Angle Orthogonal drawing.

 

 

Back to top

 

A projection

 

Watch the video above to see how we can draw a three-dimensional object on a flat piece of paper by 'projecting' the views away from the object onto planes. In the video these planes are shown as a glass box. This set of flat planes are then folded out and become the paper on which the drawing is made.

 

A 3rd Angle Orthogonal drawing is a way to show a three-dimensional object on a flat piece of paper. As you would realise we can't really draw all the sides of an object at once, unless we are Pablo Picasso! We neeed to separate the views and draw them one at a time.

 

Which angle? 1st or 3rd?

 

Why is the drawing called a '3rd Angle' Orthogonal? What happend to the 1st and 2nd angle? The reaseon is to do with where an object is situated relative to the 'paper'. So consequently, how it's views are projected. As you saw in the video of 3rd Angle orthogonal projection, the views are projected up and away from the object. It is as if we are tracing the views on the glass box.

 

3rd angle

 

We look through the views to the object in 3rd Angle projection.

 

However, in a 1st Angle orthogonal projection the views are not projected up and away from the object but appear like a shadow behind and below it as if the viewer is wearing a headlight torch. Does 1st or 3rd Angle make much difference to the drawing?

 

It makes a big difference. In a 3rd Angle Orthogonal the views of an object appear on their natural sides. That is, a RIGHT SIDE VIEW is on the right of a FRONT VIEW. But, in a 1st Angle Orthogonal a RIGHT SIDE VIEW is shown on the left of the FRONT VIEW! Think of the trouble you could get into building something from a drawing if you didn't know if your drawing is in 1st or 3rd Angle.

 

1st Angle

 

But in 1st Angle projections, the views are shadows of the object. This places them opposite their natural position.

 

 

 

It depends on the quadrant

 

There are many great explanations of the 'quadrants'. Click here to see one.

 

So how can we tell?

 

Simple. We use a symbol to tell us. Below is the symbol for 3rd Angle Orthogonal drawings. Note that the short side of the cone on the right is next to the FRONT VIEW. What do you think the symbol for a 1st Angle Orthogonal drawing would look like?

 

3rd Angle symbol

 

Learn to draw this every time you work witih this drawing method.

 

Back to top

 

3 Who uses them? What are they for?

 

a real engineering drawing

 

(http://eksmaoptics.com/out/pictures/master/product/2/ 840-0096drawing.jpg)

 

An Orthogonal drawing is a pretty serious kind of drawing. They contain all the details for making something. They form part of a manufacturing contract so they have to be accurate. If it's made 'according to the drawing' the builder can be paid. If it's not, the drawing will be used to show why it's wrong.

 

Various kinds of Orthogonal drawings are used by product designers, engineers, pattern makers, architects, interior designers, builders and drafts people.

 

An architectural variation on Orthogonal drawing is known as 'Plans and Elevations'.

 

Back to top

 

rules for Orthogonal drawings

 

In order for Orthogonal drawings to communicate details clearly (between designer and builder) they need to be drawn consistently. Designers need to follow a precise set of rules. There are rules for the kinds of lines to use, the ways to name things, the way to say how big things are and every other detail that needs to be shown in the drawing. The name for the rules in our country is 'Australian Standards AS1100.'

 

The VCAA interpretation of AS 1100 can be seen by clicking here. This booklet includes all the information you need for Orthogonal drawings in our study all the way to Year 12.

 

The full AS 1100 can be purchased from SAI Global. Follow this link.

 

Back to top

 

 

4 setting out an orthogonal drawing

 

Orientation of the TOP VIEW

 

Before we start. There are two alternative orders in which we can draw orthogonal drawings. Some people draw from to bottom up, others draw from the top down. I prefer to draw from the top down. Conisider this chair:

 

 

When we start out we are faced with a choice. Which way do I orientate my TOP VIEW? Should I draw it like 'a' or 'b'.

 

plana planb

'a'

'b'

 

The answer lies in how the view below the 'TOP VIEW' will end up. If I chose 'a' above, the drawing below it will look like 'a' below. If I chose 'b' above, the drawing below it will look like 'b' below. Which is right? Is there really a right answer?

 

front a front b
'a' 'b'

 

Yes, there is. Now look at the following picture:

 

 

This is a 3rd Angle Orthogonal drawing of a box. There are three views in the drawing. Like the church in the animation, there is a TOP VIEw (looking down on the box). Then notice the name of the view under the TOP VIEW. It is called the FRONT VIEW. Is it really the front of the box? We don't know. It doesn't matter. What matters is that we know that the view that is under the TOP VIEW is always named the FRONT VIEW!

 

So back to the original question. Which is the correct way to draw the TOP VIEW of the chair? The Australian Standards says that the FRONT VIEW is the view that contains the most information about the form of the object. Therefore, the correct answer is 'b'. Draw the TOP VEIW so that the FRONT VIEW shows the side of the chair because this tells us more about the form of the chair.

 

Back to top

 

Correct set out

 

The first step to drawing in Orthogonal projection is to make sure your views are set out so they are aligned properley. When you draw the first vertical line for the first view, draw it long enough for both TOP and FRONT views. The drawing below shows how each view is aligned with the other views. The FRONT VIEW is perfectly below the TOP VIEW. The RIGHT SIDE VIEW is on the same line as the FRONT VIEW. Look along the blue lines to see the views line up.

 

correct set out

 

 

Learning task

 

Make a 5 minute freehand sketch Orthogonal drawing of this 'Monopoly' house. Don't worry about the scale or proportions of the house, just make sure your views are correctly aligned with each other. You have to think ahead to leave enough space for each view.

 

try this out...

 

You can add a door and chimeny too.

 

Back to top

 

5 Lines in australian standards

Orthogonal drawings are 'read'. Because they are legally binding documents for engineers, builders, archtects, etc, each line drawn on them has meaning. There are two ways to talk about lines;

Line type

 

Look at the following table for different kinds of lines;

 

australian standards lines

 

From; http://www.vcaa.vic.edu.au/Documents/vce/visualcomm/technical_ drawing_specifications.pdf Page 12 (Retrieved 22 February, 2013)

 

 

Continuous lines

 

Continuous lines are used for Outlines and Dimension lines, Leaders and features that are not structural parts of an object.

 

Dashed lines

 

Dashed lines made of even parts; line and space, are used to show details of a drawing that are below the surface of an object. These lines are called HIDDEN lines.

 

Chain lines

 

Chain lines made of different length lines and spaces are used to show centres of circles, axis of cylinders, and Cutting planes.

 

Back to top

 

Line strength

 

Thick lines

 

Thick or heavy lines are used for outlines of each part or view. Thick lines are also used for Hidden lines.

 

Thin lines

 

Thin or light lines are used for Dimension lines, Leaders (arrows), Writing and other elements that are not structural parts of an object in a view. Thin lines are also used to indicate Centre lines to show the centre point of a circle. This is also not a structural part of an object.

 

Actual Line Widths

 

 

Thick lines

Thin lines

Drawing with pencil

HB heavy pressure

HB sharp, light pressure

Drawing with technical pen or fineliner

0.35 mm

0.18 mm

Drawing on computer

Stroke 1 pt

Stroke 0.5 pt

 

Back to top

 

6 Drawing an Orthogonal drawing

 

Follow the directions shown in this video to make a drawing of the Monopoly house shown above, to scale. Use a tee-square and set-squares.

 

try it for your self

 

Watch this video and draw your 3rd Angle Orthogonal drawing.

 

Back to top

 

7 application of australian standards


Hidden lines

 

Look at the drawing shown below. When there are details that are below or inside the surface of the object, show them with a dashed line. Hidden lines are normal thick lines.

 

hidden lines indicate internal structure

 

A dashed line is used to indicate internal structure or parts we can't see from the outside.

 

 

Back to top

 

Centre lines

 

Use chain lines for centre lines for circles. You must show a centre (axis) line in the TOP VIEW and a centre cross in the other VIEWS. Centre lines are thin lines and go over other details.

 

chain lines indicate centres and lines of axis

 

Don't forget to show centre lines on each view in the correct way.

 

 

Back to top

 

Naming views to Australian Standards

 

Each separate view in an Orthogonal drawing has a name. But remember, the names of the views doesn't relate to the names of the actual view of the object. The names of the views relate to the position of the views relative to the TOP VIEW in the whole drawing. Here is a picture of all the views in the correct position relative to the TOP VEIW.

 

lable positions

 

Don't forget to show centre lines on each view in the correct way.

 

 

Back to top

 

Drawing name labels

 

Name labels are done in a consistent way. Draw 'Sans Serif,' capital letters. Align them neatly on horizontal guide lines. Centre them under each view. Use the dimensions below as a guide.

 

naming views

 

This picture shows how to draw text within simple contstruction lines.

 

Back to top

 

title blocks and borders

 

Drawing your type

 

Use guides to align your letters. Draw the same sans serif capital letters as you did for the view labels. Here is a guide to how to set out your words in the title block;

 

title box type

 

This picture shows how to locate and draw drawing title information at the bottom of your sheet.

 

 

Your finished 3rd Angle Orthogonal drawing should contain a border and a title block. There is not set way to do this but they should be done neatly and accurately.

 

Dimensions of the border

 

A border is drawn around the edge of the page. On A3 and A2 it is usually drawn 20 mm in from the edge of the page. On A4 it is drawn 10 mm from the edge.

 

Dimensions of a title block

 

The title block is drawn at the bottom of the sheet. This usually extends right across the sheet as shown in the example at the top of this page. Make your title block 20 mm high.

 

Contents of a title block

 

Your title block typically includes the following information;

 

Back to top

 

Dimensions

 

Dimension are the measurements of things and are used on Orthogonal drawings to show sizes of objects or parts of them.

 

Dimension rules

 

There is a set technique for drawing and labeling dimensions. Here are the components of dimensions on Orthogonal drawings.

 

  1. Extension lines
    • These are the lines that extend from points on the drawing outwards. They are an extension of existing lines on the drawing. They do not touch the drawing, but begin about 2 mm from the edge of the drawing. They extend just past the dimension line. They are thin lines.
  2. Dimension lines
    • These are drawn parallel to the object. They just touch the extension lines at each end. These are thin lines.
  3. Arrow heads
    • These are little triangles about 3 mm long and 2 mm wide. They are coloured in solid black. Each dimension line begins and ends with an arrow head.
  4. Numbers
    • Dimension lines carry the measurement of the length of the dimension. Draw numbers in the same sans serif font as your name lables. The numbers show the actual length on the real object not on the drawing regardless of the scale of your drawing. Do not write 'CM' or 'MM' beside the numbers, do this in the main title boxof the sheet. Do not break the dimension lines for the numbers. On vertical dimensions you may write the numbers horizontally or vertically - as long as you do it consistently on each dimension of the drawing.
  5. Dimensioning circles
    • Circls are shown by marking the diamater of the circle. Leaders are the name for the arrow used. They touch the edge of the circle. See below for an example.

Dimension process

 

See below for the process of creating dimensions. Remember carefull planning is required for accurate work.

 

Adding dimensions to your drawing

 

Draw a set of construction lines to help you locate your projection and dimension lines. You will need 3 lines for each dimension line, as you have to form up your arrows. The red circles indicate the gap between the object and the extension lines.
Once you have your construction lines you can draw in the final extension and dimension lines. Extension lines (the vertical ones here) begin 3 mm away from the object and project 3 mm past the dimension lines.
Draw in a pair of 3 mm wide arrows at the ends of your dimension lines. They are neat triangles and are coloured in.
The numbers to indicate dimension are written above or to the side of the dimension line. The numbers refer to the actual size of the real object. The scale of the drawing takes care of what length the object in the drawing appears to be. Do not include the unit of measurement (Millimetres, Centimetres, etc). The unit of measurement is written in the title box of the drawing.
With construction lines removed, you can see one set of dimensions.
Draw dimensions on the other side, keep your dimension numbers horizontal. Do not break the dimension line.
Locate your centre 'cross' chain in the correct place first.
To dimension a circle draw a leader extending from the edge of the circle at 45 degrees. The leader must touch the circle but not overlap it. Draw the same kind of 3 mm arrow head at the end of your leader. The size of the circle is annotated by a numeral and the symbol for diameter.
To do intermediate dimensions you have to plan them carefully. This example is INCORRECT! You must not cross extension lines.
This drawing shows the CORRECT way to do intermediate dimensions. The larger ones go outside the smaller ones.
The completed dimensions. You are asked to show overall dimensions that indicate the Length, Width and Height of an object as well as some intermediate dimension and the size of circles.

 

Back to top

 

Scale

 

You will do your 3rd Angle Orthogonal drawing to a scale. A scale means the relationship between the real object and your drawing. In most cases you will have to do some maths to work out an appropriate scale to use.

 

For product design use; 2:1 (twice as big as the original object), 1:1 (same size), 1:2, 1:5 or 1:10 (half size, one fifth or tenth of the size). To work in your scale you have to multiply or divide your dimensions. How long is a line 1 metre long in the scale of 1:5. (1000/5 = 200. It's 200 mm long, or 20 cm.)

For architectural design use; 1:20, 1:50, 1:100 or 1:500.

 

Two further tips for working with scales.

 

  1. Don't make up your own scales even if they will help your drawing to fit on the paper better. Scales are part of the standards and conventions you are using.
  2. Draw the lines in scale but write the dimensions on your drawing as if they are the real line.

Back to top

 

8 Sectional drawings

 

A Section is a short way of saying 'cross section'. It means how something looks when it is cut through. Sectional views are used to show how something looks inside. There are several components to sectional drawings.

 

Cutting plane

 

This marks the place where the object is 'cut'. This is usually shown on the TOP VIEW. The cutting plane is shown by a thin line across the drawing with two large flat arrow heads. The direction of the arrow heads indicates the direction of view for the sectional view. There are also letters given next to or below the arrow heads. This names the section. In a drawing there may be several sectional views; A - A, B - B, etc.

 

Cross hatching

 

Solid material is shown with a texture of thin parallel lines drawn at 45 degrees. This is know as 'cross hatching'. Different physical parts of an object are shown with the cross hatching drawn in the opposite direction.

 

Positioning of the section in the drawing

 

The sectional view can be drawn 'out of the normal place' for the view that it is. It is normally shown aligned with another view (like in the example) below.

Look at this example; Note the hidden lines have been replaced by continuous lines. Why is this?

 

cutting plane and sectional cross hatching

 

Note the way the arrows indicate the viewing direction and the cross hatching indicates solid material.

 

 

Back to top