The »bility to sketch neatly and accurately is one of the most useful attributes that a draughtsman can have. Freehand drawing is done on many occasions: to explain a piece of design quickly to a colleague; to develop e design (see Fig. 16/10); and even to draw a map showing someone how to get from one piece to another.
Technical sketching is a disciplined form of art. Objects must be drawn exactly as they are seen, not as one would like to see them. Neat accurate sketches are only achieved after plenty of practice, but there are some guiding rules.
Most engineering components have outlines composed of straight lines, circles and circular arcs: if you can sketch these accurately, you are halfway towards producing good sketches. You may find the method illustrated in Fig. 16/1 a help. When drawing svaight lines, as on the left, rest the weight of your hand on the backs of your fingers. When drawing curved lines, as on the right rest the weight on that part of your hand between the knuckle of your tittle finger and your wrist. This provides a pivot about which to swing your pencil. Always keep your hand on the inside of the curve, even H it means moving the paper around.
STAGE 1 (CONSTRUCTION)
STAGE 2 [LINE IN AND DETAIL)
STAGE 1 (CONSTRUCTION!
(LINE INLAND DETAIL]
STAGE 3 (SHAOE)
Sketching in Orthographic Projection More detail can be seen on an orthographic drawing than on an isometric, mainly because more than one view is drawn. For this reason it is often advantageous for a draughtsman to make an orthographic sketch.
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The views should be drawn in the conventional orthographic positions, i.e.. in 3rd angle projection, a F.E.. a plan above the F.E end en E E. to the left or right of the F.E.; in 1 st angle projection, a F.E.. a plan below the F.E. end an E.E. to the left or right of the F.E. These views should be linked together with projection lines
Figs 16/8 and 16/9 show pictorial and orthographic sketches of two engineering components.
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Circles are difficult to draw freehand but you can use your hand as a compass. Hold your pencil upright and. using your little finger as a compass 'point', revolve the paper keeping your hand quite still.
Fig. 16/10 shows how a draughtsman might use sketching to aid a piece of design. He wishes to design a small hand vice.
First he makes a freehand pictorial sketch so that he can see what the vice will look like. He also makes a few notes ebout some details of the vice.
He then makes an orthographic sketch. This shows much more detail and he makes some more notes.
This is quite a simple vice and he may now feet that he is ready to make the detailed drawings. If it was more complicated he might make a few more sketches showing even more detail. Details of one of the lags of the vice are ahown.
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