Page 37 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

Hidden lines: Correct and incorrect method in sketching/drawing hidden lines are shown in Fig 8.

Fig 8

The following rules can be adopted for the drawing of hidden lines.
– Leave a gap wherever a hidden line dash forms a continuation of a visible line. (Fig 8A)
– A hidden line should intersect to form `L' or `T' corners. (Fig 8B)
– A hidden line preferably should jump a visible line. (Fig 8C)
– Parallel hidden lines should be staggered. (Fig 8D)

– When two or three hidden lines meet at a point, the dashes should join. (Fig 8E)
– For showing the counter sunk hole. (Fig 8F)
– Correct and incorrect methods of hidden arcs. (Fig 8G & H)
Centre lines: Centre lines are used to indicate arcs of symmetrical objects or features. Fig 9 shows the typical
applications of the centre lines in various features.
Meaning of lines: A hidden line or a visible line has the following meanings
– Intersection of two surfaces
– Edge view of a surface

– Contour view of a curved surface. (Fig 10)
Procedure line: Hidden lines, centre lines and visible lines often coincide with each other and it is needed for
craftsman to know which line should be shown. Fig 11 explains the same. A visible line is always precedence over
(corners up) a centre line or hidden line A & B of Fig 11. A hidden line is always takes precedence over a centre
line at c of Fig 11. (3rd angle projection)

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CITS :Engineering Drawing (Mechanical) - Exercise 3