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Technical Drawing - Coggle Diagram
Technical Drawing
Orthographic projection
Orthographic projection is the method used to draw a 3D object on flat paper using parallel rays that hit the
paper at 90°
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The three views
An object has six sides, so it has six possible views. In class we draw three: the ones that carry almost all the
information. To get them, imagine the object floating inside a glass box: you look at it from the front, from the top
and from one side, and each view is painted on the glass behind it. Then the box is opened flat like a cardboard
box.
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First and third angle
There are two standard ways of placing the views, and they give the same three views — only their position on
the sheet changes. Europe (and Spain) uses the first angle, also called the European system. Industry in the USA
and Canada uses the third angle. To tell you which one a drawing uses, every technical drawing carries the norm
symbol (símbolo normalizado): a cut cone, drawn as a trapezoid plus two concentric circles.
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Scale
A real object rarely fits on a sheet of paper. The scale tells you how many times bigger or smaller the drawing is
than the real thing. It is written drawing : reality, so in 1:2 the drawing is half the real size, and in 2:1 the drawing is
twice the real size
One plate, 60 mm × 30 mm, three times
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Visible, hidden and centre lines
A technical drawing is read by the type of line, not by the colour. Four line types carry almost everything, and the
drawing uses a fixed rule of thickness: thick lines are twice as thick as thin ones (about 0.7 mm and 0.35 mm
when you draw by hand).
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