Elements of mechanical drawing.. by Anthony Gardner

Author:Anthony, Gardner, [Chace] [from old catalog]
Language: eng
Format: epub, pdf
Publisher: [n.p.]
Published: 1904-03-25T05:00:00+00:00

Fig. 121.

ORTHOGRAPHIC PROJECTION

Fig. 124-.

101. The projection and true length of lines. Fikst Method. Let A"B" and A^ B^', Fig. 122, represent two views of a line inclined to the coordinate planes H and V. It is required to find its length and the angles which it makes with the H and V planes of projection.

Since the line is inclined to both jjlanes, its ^Ji'ojections on them will be foreshortened views of the line. In order that the line shall be parallel to one of the planes, and thus seen in its true length on that 2jlane, it will be necessary to revolve it about an axis jjerpendicular to one of the planes according to the principles already established for the revolution of an object. Art. 97, page 67. It may be revolved about an axis perpendicular to H until it becomes parallel to V, or about an axis perpendicular to V until parallel to H. Fig. 123 represents the line revolved parallel to V, the revolved position being shown by A^ B'. The horizontal projection of the line, which in the revolution about a vertical axis we know to be unchanged, is first drawn parallel with the ground line, in which position the line will be parallel to V. The height being unchanged the vertical projection may next be obtained, and the representation will be that of a line parallel to V and therefore seen in its true length on that plane. This view also shows the correct angle, R, which the line makes with the horizontal plane, since its position relative to that plane is unchanged by the revolution.

Similarly the line may be revolved about an axis perpendicular to V until it is parallel to H, as in Fig. 124, when its true length may be

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