A First Course in Engineering Drawing by K. Rathnam

Author:K. Rathnam
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

17.A right square pyramid, edge of base 30 mm and height 60 mm, is suspended freely from a corner of its base. Draw its projections.

The centre of gravity of a pyramid/cone lies on the axis at a distance equal to ¼ axis from the base. The line connecting the corner of suspension with the centre of gravity will be vertical when suspended freely. The base of the square pyramid is kept parallel to the HP and above the apex/vertex with the base edges equally inclined to the VP. The projections are obtained. The pyramid is suspended from one of its extreme corners. The pyramid moves parallel to the VP so that the line joining the extreme corner and the centre of gravity is perpendicular to the HP. The plan is projected from the elevation.

Draw the reference line xy and the plan of the square pyramid with its base above the apex and parallel to the HP as shown in Fig. 10.26. The base edges are equally inclined to the VP so that the square pyramid can be suspended from one of its extreme corner. The elevation is projected from the plan. The centre of gravity g′ is located on the axis 15 mm from the base in the elevation. The plan of centre of gravity g coincides with the axis of the pyramid. The pyramid is suspended from b′ so that the line passing through b′ and g′ is perpendicular to xy. The pyramid moves parallel to the VP. The elevation is redrawn as shown in the figure. The plan is to be projected from the elevation. A projector is drawn perpendicular to xy from d1′. The locus line is drawn parallel to xy from d. The intersection of the projector with the locus line locates d1. The same procedure is followed to get a1, b1, c1 and e1. These points are joined to show the edges of the pyramid in the plan with a part of invisible edge a1d1 shown as dotted.

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