resumen

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UNIT 4: Technical drawing
Drawing
1. Types of drawings
A drawing is a way to express an idea.
Therefore, it is a method of communication.
•Artistic drawing → feelings.
Examples: a painting, a cartoon
•Technical drawing → communicate
technical info by representing objects.
Examples: a sketch, a plan

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2. Drawing materials and instruments
2a) Paper
This is the most commonly used drawing surface. Its size
is standard. From A0 standard (1m2
), we fold the sheet
by its longer side again and again getting the standards.
Standard Dimensions (mm.)
A0 1189 x 841
A1 841 x 594
A2 594 x 420
A3 420 x 297
A4 297 x 210
A5 210 x 148

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•Activity 1: Calculate the size of A6
and A7 standards.
Activities

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2b) Drawing instruments
•Pencil: According to lead hardness
B: soft
HB: medium
H:hard
•Technical pen: to draw in ink
•Ruler
•Protractor
•Set squares: 45-45-90 and 30-60-90 set squares
•Compass

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3. Basic procedures: measuring and drawing
Measuring with a ruler
Drawing parallel lines Drawing perpendicular lines

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Drawing an angle with the protractor
Drawing circles and arcs
with the compass

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•Activity 2: Measure and write down the length of your
rubber and your pencil.
•Activity 4: Draw an oblique line and 2 segments 15mm.
and 1cm. long on this line.
•Activity 5: Draw an oblique line and 2 parallel lines to
the oblique line.
•Activity 6: Draw an oblique line and 2 perpendicular lines
to the oblique line.
Activities
•Activity 3: Draw 3 segments 38mm, 1,4cm and 42mm
long, one below the other, and label them with their
length.

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•Activity 7: Draw a horizontal line (see illustration below).
With the set squares, draw the following angles: 30º, 45º,
60º, 75º, 90º, 120º and 150º. Then, check it with the
protractor.
•Activity 8: With the protractor, draw the following angles:
43º and 125º.

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•Activity 10: Draw a circle with a radius of 4 cm.
•Activity 11: Draw an equilateral triangle with a side of 5
cm. (with the help of the compass)
•Activity 12: Draw a square with a side of 6 cm. (with the
help of the compass)
•Activity 9: With the set squares and the compass, draw
the following letters (4 cm. height):
IES

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4. Sketch and plan
•Sketch:
It is usually a freehand drawing that shows a first idea of
an object. However, it can be drawn using a ruler.
Sometimes, it includes text.
•Plan:
It is a detailed drawing made by computer.

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Activities
•Activity 13: In your notebook,
make a sketch drawing of a chair.

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5. Annotation
Annotation is adding text to your drawing to show
the actual dimensions of an object.
Annotation
elements
•Dimension text: with measurement
units.
•Auxiliary or extension lines
•Dimension line: parallel to the edge
and ended in arrows.

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Activities
• Activity 14: Find and explain the annotation
mistakes in the following figures:
20
6 cm.
7
5
26 cm.
a) b) c)
d) e)

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6. Views of an object
Used to represent a 3D object on a 2D (flat) surface.
Main views
•Front view
•Top view (Plan / Overhead)
•Left side view
Front Left side
Top

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Top view
Front view Left side view

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Activities
•Activity 15: Worksheet on Views

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7. Cavalier perspective
Width, height and depth are shown.
A Depth Ratio of 0,7 is used in order to look real.
This is another way to represent a 3D object on a
flat surface.
Procedure:
1. Draw the front view
2. Draw lines at 45º from every
vertex
3. Complete the figure with
parallel lines (do not forget
about the Depth Ratio)

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Activities
• Activity 16: Using cavalier perspective
draw the following objects :
Rubber
Pencil sharpener
Mobile phone

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8. Scale drawing
Scale: Ratio between the dimensions of the
drawing and the dimensions of the actual object.
Scale=
Drawing length (D)
Actual length (A)
S =
D
A

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Scale Types
•Enlarged scale: D>A e.g. 2:1, 50/1
(cell, mosquito)
•Reduced scale: D<A e.g. 1:5, 1/100
(Map, room, house)
•Actual scale: D=A e.g. 1:1
(pencil sharpener)

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Example 1: Draw the figure below at a scale of
S=1/2 and at a scale of S=2:1.
S=1:1 S=1/2 S=2:1
2
2
4
6
2
Numbers = little squares in your notebook

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• Activity 17: Draw the views of your desk at a
scale of S=1/10. To do so, you have to measure
the dimensions of your desk.
Activities

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•Activity 18: What type of scale must be used to
represent the following objects: a nut (screw), a flat,
a table, a crayon, an atom.
•Activity 19: Draw the front view of
a glass, 5 cm. height and radius of 1
cm. These measurements belong to
a drawing at a scale of 1:3. What
are the actual dimensions (height
and diameter) of the glass?
5
cm.
Radius= 1 cm.
S= 1/3