1. Designing things on paper
Technical Drawing
Designing things on paper

3. Conceptual Sketches
When you first get an idea for something you want to build you may draw it roughly, without using instruments or accurate scales. This is called a conceptual sketch.

4. (technical/engineering) simulated perspective
Types of Drawings
All Drawings
Artistic
Technical
Sketches
(conceptual)
Diagrams
(design & technical)
Drawings
(technical/engineering)
simulated perspective
Diagram
(design plan)
Diagram
(technical)
Oblique
projection
Isometric
projection
Multi view
orthographic
Less technical More technical

5. A conceptual sketch…
Allows an idea to be expressed quickly in graphic form
Is prepared free-hand (without drawing instruments)
Is not done to scale, but it respects the rules of technical drawing as much as possible, and is made roughly proportional to the object represented.

6. Technical Drawings
Serve as a reference to workers, architects or machinists.
When you are ready to design the details, you make a technical drawing, done with more detail and more accuracy.

7. Difference:
Sketch: made without drafting tools... Just pencil and paper. Scale is approximate, not accurate, but the sketch should still look like the object.
Drawing: made with drafting tools... Ruler, set squares, protractor and compass. Scale should be accurate and the drawing carefully made.

8. A technical drawing…
Presents all the information necessary for the object’s construction.
Is made with great precision,
Requires the use of rulers, compass and protractor or drafting software.
Is done to scale, and respects the proportions of the object represented.
Respects conventions in the mode of the representation.

9. Basic Lines (part 1) Visible (Object) Line Represents the outline
Thick
Draw the visible object edges with these lines
Hidden Line
Shows hidden details
Medium dashed
Draw hidden edges with these
Construction Line
Used during drafting
Fine
Faint lines, sometimes coloured
Dimension Line
Used to indicate a dimension
Fine,
with arrows
8cm
Dimension & extension lines go together!
Extension Line
Used with a dimension line
Near arrows
Center (Axial) Line
Shows center or symmetry
With dash in middle
8 cm

10. Basic Lines (part 1) Ghost Line Shows possible movement Fine
dashed
Sometimes in other color
Cutting plane line
Position of a cross-section
Thick
With arrows
Used only if you plan to draw a cross section
Hatched
Lines
Surface of a cross-section
Show where it is solid (section view only!!)
Long Break
Shows that a line is shortened
With zig-zag
Used only for large objects
Short break
(cutaway)
Object shortened or cut away
Medium
With curve
Leader Line
Points to something
With bent arrow
Attaches a comment or angle or dimension to an object.

11. Technical Drawing of Fighter Plane (Isometric Projection, exploded view)

12. Technical drawings can represent things…
as simple as a spoon,
or…
Technical Drawing of a spoon
Multi-view, Orthographic projection

13. as complex as a space ship
Photograph of Mercury Spacecraft
Technical Drawing of Mercury Spacecraft, Top View, Orthographic
 Technical Drawing of Mercury Spacecraft, Isometric Projection

14. Projections Perspective projections Multi-view projections
Isometric projection
Oblique projection

15. True Perspective Objects drawn in true perspective look realistic.
Vanishing Point
True Perspective
Objects drawn in true perspective look realistic.
They have “vanishing points” where straight lines seem to converge
They can have one, two or three vanishing points, depending on how much the artist wants to work.
But in true perspective, objects far away will be drawn smaller than nearby objects… not a good idea in technical drawing!
Vanishing Points
Vanishing Points

16. More True Perspective Drawings

17. Now that you have seen how nice perspective drawings can be...
FORGET ABOUT THEM!
We hardly ever use perspective projections when doing technical drawing.
They are too much work, and they don’t show all the details we may need to show.
Also, they distort both angles and dimensions.
Leave them for ART class...

18. Isometric Projection (a simulated perspective drawing style)
Isometric (or simulated perspective) drawings look at first like perspective drawings…
But the lines don’t converge. There are no vanishing points and distant objects are the same size as nearby ones.
Right angles in isometric projections are usually represented by 60° or 120° angles.
60˚
Represents 90˚
Represents 90°

19. More isometric drawings
Warning: Your workbook classifies isometric drawings as “perspective” drawings, but they are not true perspective. They resemble perspective drawings but in a true perspective drawing, distant objects are drawn smaller. In isometric drawing, distant objects are not smaller..

20. Oblique Projection another “simulated” perspective
Similar to isometric projection, it is also a “simulated perspective”
In oblique projections, the side of the object facing you is drawn “square” and accurate (that is with right angles at 90° and its measurements proportional)
The sides not facing you are distorted
Warning: Your workbook calls this oblique perspective, but it is not a true perspective.
This side is not!
This side is accurate
90°
=60°
90°

21. Orthographic Projections
Orthographic projections “flatten” one view of the object onto a sheet of paper, while retaining the correct proportions (angles and dimensions)
Maps are an example of orthographic projection (a top view)
The trouble with orthographic projections is that one view usually isn’t enough.
Maps and floor-plans are exceptions, where one top-view is often enough.

22. Orthographic Projection (Multi-view)
Draws an object as it would be seen from several different directions
The views are “flat”, with all angles shown correctly and all measurements to scale.

23. Comparing Projections
Perspective drawings look nicer when used by an artist, but…
Isometric, oblique and multi-view drawings give more accurate information when used in technical drawing.
Isometric drawings show accurate dimensions, but distorted angles.
Oblique drawings give accurate dimensions for one side only.
Orthographic (multi-view) are the best choice for most technical drawing.
Oblique
Orthographic
(multi-view)

24. Comparison of Projections
Used for
Tested on
Orthographic
(top view)
Drafting, maps, floor plans
Yes
(multi-view)
Technical drawings, drafting, conceptual sketches (sometimes)
True Perspective
(one, two or three point)
Artistic drawing, conceptual sketches No
Isometric
(simulated perspective)
Conceptual sketches, technical drawings (sometimes)
Oblique
Conceptual sketches

25. An Isometric Drawing

26. Scale
SCALE is the relationship between the measurement of an object drawn on a sheet of paper, and the measurements of the actual object.
Often technical drawings are made a different size from the objects they represent.
Scale-reduction is when the drawing is smaller than the actual object
Scale-increase is when the drawing is larger than the actual object.

27. Dimensioning
When a drawing is done to scale, you should label it with its dimensions.
Use dimension lines to label each dimension, with extensions where necessary
You should label just enough edges to show all the dimensions, but you don’t need to repeat.
In Canada (at least for science) dimensions are usually given in millimetres (mm). If you use different units (cm, in, feet etc.) you need to write the unit. You do not need to write mm if all of your dimensions are in millimetres.
Angles can be shown in degrees (°), diameter by Ø, and radius by R

28. Dimensioning A Toy Truck 300 means 300mm How to label an angle.
unless another unit is specified
Dimensioning
A Toy Truck
How to label an angle.
Ø means diameter
(R would be radius)
How to label small dimensions.

29. Dimensioning
Dimensions can also be shown on isometric drawings, but you have to be a bit more careful. Also, you should only show the most important dimensions on an isometric drawing.

30. Diagrams
Diagrams are simplified versions of a drawing. Diagrams show how an object works, not necessarily how it looks.
Diagrams often use abstract symbols rather than actual pictures to represent things.

31. A Circuit Diagram
Doesn’t show what the circuit looks like, but tells an electrician how its all connected.

32. Diagram of Energy Conversion Unit
It doesn’t show what the unit looks like, but rather, what it does or how it works.

33. Exploded Views
A diagram that shows an object “taken apart” is sometimes called an exploded view.

34. Define: Technology Technical Drawing Basic Lines Geometric Lines
Sketch Projection
Isometric (projection) Oblique (projection)
Orthagonal (proj.) Multiview (projection)
General drawing Exploded drawing
Detail drawing Scale
Dimensioning Tolerance
Section Cross section
Diagrams: design, technical, and circuit

35. Basic Lines to Know Visible(or object) Hidden Construction Centre
Dimension and extension
Cutting Plane
Hatching
Leader (or reference)

36. Geometric Lines to know
Horizontal (straight)
Vertical (straight)
Oblique
Ellipse (and circle)
Curve

37. Methods of Drawing Sketching Drafting
Computer Assisted Design (C.A.D.)

38. Projections
Multiview (orthagonal)
Isometric
Oblique

39. Scale
Dimensioning
Calculating Scale