1. Basic Lines and Projections Scales Cross-Sectional Views and Sections
Graphical Language
Basic Lines and Projections
Scales
Cross-Sectional Views and Sections

2. Part One Basic Lines and Projections

3. Technical Drawings
In the technological world, a number of drawings are necessary in order to communicate the size, materials, function and other important parts about an object.
Each type of technical drawing has a specific role in what it demonstrates.
Each technical drawing must also be done in such a way that it uses normalized symbols and lines. This is an international language in drafting.

4. Symbols for Movement and Force

6. CONVENTIONAL LINES
FACING
DEEP
In a technical drawing, each type of line has its own significance. Each is distinguished from the other by a particular thickness or shape.
The object above is drawn in isometric projection. It is portrayed on the left by three views. We will use this object to illustrate the principal lines found in technical drawing on the slides which follow. 6

7. CONVENTIONAL LINES A
OBJECT LINE OR VISIBLE OUTLINE 7

8. CONVENTIONAL LINES OBJECT LINE OR VISIBLE OUTLINE
The object line or visible outline is made of a continuous line that portrays the visible forms of the object.
It is a thick line, its thickness chosen to clearly show the shape.
OBJECT LINE OR VISIBLE OUTLINE 8

9. CONVENTIONAL LINES B
HIDDEN FEATURE LINE 9

10. CONVENTIONAL LINES B HIDDEN FEATURE LINE
The hidden feature line is made of a dashed line that portrays surfaces and edges that are hidden from view.
The line is medium sized, half the width of the one chosen for the visible outline. B
HIDDEN FEATURE LINE 10

11. CONVENTIONAL LINES C C
THE CENTER LINE 11

12. CONVENTIONAL LINES THE CENTER LINE
The center line is made from phantom lines. It is used to designate the axes of circular or cylindrical shaped objects.
The line is half the width of the one used for hidden features. It is a fine line.
THE CENTER LINE 12 12

13. CONVENTIONAL LINES
Your Turn 13

14. CONVENTIONAL LINES
SketchUp Answer – Visible Lines 2 14

15. CONVENTIONAL LINES 15

16. CONVENTIONAL LINES 16
SketchUp Answer – Hidden Center Line 19

17. CONVENTIONAL LINES 17

18. CONVENTIONAL LINES SketchUp Answer – Hidden Lines 818
SketchUp Answer – Hidden Lines 8
SketchUp Answer – Hidden Lines 10

19. Technical drawings must not only faithfully reproduce the shape of objects, but also serve as a guide to their construction or manufacturing.
Dimensioning an object means giving all the necessary dimensions to build a technical object.
Ø 8
FACING Ø14 X 3 DEEP 80 50 45
40° 13 20 40

20. CONVENTIONAL LINES D
DIMENSION LINE 20

21. CONVENTIONAL LINES DIMENSION
The dimension is a value used to indicate size in a technical drawing.
This value is given in millimetres. 40 20
40° 45 80
DIMENSION 21

22. CONVENTIONAL LINES 50 13 40 20 24
40° 45 20 E 80
EXTENSION LINE 22

23. CONVENTIONAL LINES EXTENSION LINE
Extension lines are fine lines that indicate the placement of the dimensions. 50 13 40 20 24
40° 45 20 80
EXTENSION LINE 23

24. CONVENTIONAL LINES SUMMARY A B C D E F G H J LINE NAME PURPOSE
THICKNESS
100 %
Thick A
Object line or visible
outline
Portrays visible forms. B
Hidden feature line
Portrays surfaces and edges that are
Medium 50 %
hidden from view C
Portrays the center of a round or circular
Fine 25 %
Center line
object. D
Is used to indicate the dimension.
Extension line
Fine E
Is used to indicate the dimension.
Dimension line
Fine F
Cutting plane line
Indicates the placement of an
Very thick
imaginary cut. G
Indicate the surface imagined to have
Section lines
Fine
been cut. H
Used to shorten the view of a part.
Break line
Fine J
Indicates the part of a drawing to which
Fine
Leader
a note refers 24

25. 3 Projections In drafting, 3 projections are common: Multiview
Isometric
Oblique

26. Multiview Orthographic Projections
This looks at the six sides of a 3-dimensional object. Each side is represented 2-dimensionally.
Usually, we look at only three sides: top view, side view and front view.

27. Multiview Orthographic Projections
TOP VIEW
Here is the usual representation of views in multi-view orthographic projections.
This type of drawing is used in technology because it allows description without deforming the faces of objects. 27
FRONT VIEW
RIGHT SIDE VIEW

28. Isometric
An isometric projection rotates the object with respect to the observer so that all three dimensions can be seen in one view.
These look more like a picture than other projections.
No surface of the object is parallel to the paper.

29. A cube shown with this type of projection pivots 45º to show two faces on the projection plane instead of a single face.

30. Isometric drawing Grids and isometric drawing
A grid which includes all three isometric axes may be used to draw isometric perspectives. 30

31. Oblique
Like isometric, oblique drawings show the object in 3-dimensions.
Unlike isometric, oblique drawings show one side parallel to the paper.

32. Part Two Scales

33. Scales Technical drawings have a scale associated with them.
There are three types:
1. Scale reduction: The drawing is smaller than in real life.
1:50 (drawing is 50 times smaller than real life).
2. Full size: Same size as real life.
1:1
3. Scale increase: Drawing is bigger than real life.
50:1 (50 times larger than real life).

34. Part Three Cross-sectional views and sections

35. Cross-Sectional Views
In technical diagrams, the visible contours are shown with a continuous line.
Hidden contours are shown with broken lines.
Sometimes, the hidden contours are so intricate that the hidden contours lines do not make sense, and so a cross-section will be drawn.

36. …
In a cross-section, a new line called a cutting line is drawn in and will show what is on the inside of the object.
The purpose is to expose the hidden details to view, revealing the interior.