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STANDARDISATION There are rules related to technical drawing. They are used to ensure common understanding of graphic expression. The rules are edited by International Standard Organization ( ISO ). They define:
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THE SIZES OF PAPER THE ISO “A” SERIES “ A” Series paper sizes. A0 is a rectangle with an area of 1 m 2 ( square meter). Each format is calculated by dividing the previous format in half
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TYPES OF LINES AND SYMBOLS Different types of lines are used on technical drawing to represent the object. Each one of them has a different function.
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There are International Standards rules about how to draw dimensions. This means that all dimensions are always drawn the same way. Some rules are:
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Dimensions you show will always be measured in millimetres so you do not have to show units
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. Ø is the symbol used to show a diameter, while R is used to show a radius.
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The arrowheads used on the dimension line the point of the arrowheads should touch the leader lines.
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Dimension lines The length of the side of an object is indicated by a line outside the object. Dimension limit lines (leader, auxiliary) lines star 2 mm away from the object. Are perpendicular to the dimension line. Dimension figures (values) Express the measurements of the object in millimetres. Must be located in the centre of, and parallel to, the dimension line The arrowheads used on the dimension line, Indicates the ends of the dimension line. The point of the arrowheads should touch the leader lines
Definition: The scale (E) of the drawing is the relationship between measures of drawing and the real measurements of the object.
Scale (s) = Drawing Size Object Size
There are three types of scales :
Full or Natural Scale : is expressed as a scale of 1:1
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Reduction Scale : is expressed as a scale of 1:2
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Enlargement Scale : is expressed as a scale of 2:1
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REDUCTION SCALE It is used when the real size of the object to draw is larger/bigger than the paper format. How can you draw an object a reduction scale : To draw an object to reduce scale, divide the measurements by the denominator de scale How to read the measurements on a reduced scale drawing: Measure the drawing with a ruler and multiply the result by the denominator of the scale S = 1:1 S =1:2
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ENLARGEMENT SCALE It is used, when a n object is drawn larger than its real size. small objects, such as electronics components, screws, watch gears etc. How to draw an object using an alargement scale: multiply its measurements by the numerator in the scale How to read the measurements in an enlarged scale drawing: Measure the drawing with a ruler and divide the result by the numerator of the scale S = 1:1 S = 2:1
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DRAFT and SKETCH DRAFT: Is a freehand drawing and you should only use a pencil and eraser. It is draw quickly with the aim of graphically representing an idea or an object. SKETCH : It is also a freehand drawing but this has measures
Draft Sketch
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TECHNICAL DRAWING A TECHNICAL DRAWING HAS THE SAME INFORMATION AS A SKETCH BUT WE MUST USE RULER, SET SQUARES, A PAIR OF COMPASSES OR A COMPUTER TO GIVE AN EXACT PICTURE
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