Mechanical drawing by Faunce Linus

Author:Faunce, Linus. [from old catalog]
Language: eng
Format: epub, pdf
Tags: Mechanical drawing
Publisher: Boston, The author
Published: 1898-03-25T05:00:00+00:00

2nd. WJien a plane surface is parallel to either coordinate plane, its projection on that plane will be equal to the true size of the surface and its other projection will he a line parallel to GL.

drd. When a plane surface is perpendicular to one plane and oblique to the other, the angle which its projection on the plane to which it is perpendicular makes loiih the ground line is equal to the angle the surface in space makes with theplane to which it is oblique.

4th. If a plane surface, in different positions, makes a constant angle with a plane, its projections on that plane will all he of the same size.

54. Prob. 3. To draw the two projections of a plane surface, or card, of a certain size, and making a compound angle with the coordinate planes.

Let the card be of the size shown in Fig. 9, and suppose it to make an angle of 30° with H, and its horizontal projection an augle of 45° with GL.

Draw the horizontal projection a^b^c^d^ of the card equal to its true size; a^¥ will be its vertical projection. Revolve a^b'" through an angle of 30° to a^b^, and a^hj' will be the vertical projection of the card when it makes an angle of 30° with H and is perpendicular to V; a^bj^c^'^d'^ is its corresponding horizontal projection.

The angle with H is still to be 30° after the card has been revolved to its desired position, hence its horizontal projection will be the same size. Therefore, make a%]^c]^d^, Fig. 10, equal in size to a^j^cf-d^, Fig. 9, and making the desired angle with GL. In this revolution, as long as one edge rests on H and the angle remains constant with H, every point keeps the same height above H, therefore the vertical projections of a^

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