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Technical drawing, mind map scam 1, Captura de pantalla 2026-10-02 170915,…
Technical drawing
Front, top and side views
An object has six sides, so it has six possible views. We draw three. To get them, imagine the object in a box. we look at it from the top, front and side.
The object is between you and the planes, so the top view is painted on the plane on the far side.
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Once the views are placed, they are not independent: they are three pictures of the same object, so they must agree.
There are three correspondances: width, height and length.
Orthographic projection
Its is the method used to draw a 3D object on flat paper using parallel rays that hit the paper at 90°. Each ray travels straight and doesn't spread.
In orthographic, the edge is parallel to the paper, so it is drawn at its true length and the drawing can be measured.
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The rays are parallel and perpendicular to the projection plane, so the drawing keeps the true size of the object.
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 uses the first angle, and the USA and Canada use the third angle.
The symbol tells you which system is used: the circles go on the same side as the view of the left face--right in the first angle, left in the third angle.
different places use different angles, so engeneers use it to make the angle clear.
Visible, hidden and centre lines
A technical drawing is read by the type of line, not by the colour. The drawing uses a fixed rule of thickness: thick lines are twice as thick as thin ones
A plate with a blind hole. The hole cannot be seen from the front, so its walls are drawn dashed; the hole's axis is a centre line.
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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. I
Dimensions are always the real size. The scale changes the drawing, not the number.
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Dimensioning
A drawing without dimensions is only a picture: the workshop cannot build anything from it. Dimensioning is the set of thin lines and numbers that say how big the part is.
The number goes above the line (or to the left of a vertical line), never on it, and never inside the part. the lines must be outside the shape.
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2D and 3D CAD
CAD means Computer Aided Design: drawing and modelling on a computer, with exact coordinates instead of a rubber and a ruler. there are two types.
In 2D CAD you draw the lines; in 3D CAD you build the solid once and the drawing is generated from it.
An engineer builds a parametric 3D CAD model first to check if parts fit together without colliding.
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