drawn (in the example, a small clip or button) is shown piotoriallv in space. The plane upon which it is to be projected, represented bv the rectangle 1-2-3-4, stands vertically behind, and parallel with, the object; projectors are taken from each corner of the face of fhe object, at an angle of 45° with the horizontal line 1-4, until they meet the plane of projection. These points of impingement are joined by straight lines which are parallel with the edges they represent on the object, thus an exact replica of the face of the object is obtained. Next, at one of the salient angles in the picture, an arbitrary projector is drawn, such as a-a" or b -b." This projector determines the angle of the visible sides, therefore all parallel edges are projected parallel with it, anil the depth or thickness of the projection is determined by drawing projectors to intersect these, at an angle of 45f from the points on the rear face of the object, as a'-h', etc.
This method could be adapted to give a projection with the object lying at any angle to the plane of projection, but no good purpose would seem to be served by it except as a mental exercise, because the object must first be drawn pictorially, when the projection seems superfluous. Fig. 8 011 this plate is an example drawn in the half-scale method of a cube placed in the middle of a slab, and resting upon one edge, with its adjacent sides at an angle of 450 with the surface rested upon. The slab is first drawn, also a projector from the middle of the edge a ; upon this is located fhe position of the face of the cube which is drawn by aid of the set square of 450, the oblique sides being projected at 30° and made half the depth of the front sides. Fig. g is the projection of a box by the first method, to a scale of } in. to 1 ft.; it should offer no difficulty as it is merely an elaboration of the cube.
Fig. 10 is a projection of a hexagonal prism. The near surface or end is produced by using the set square of 30° to draw the two lower surfaces, marking upon thorn the required width, raising vertical sides at these points, making
Was this article helpful?