sected by horizontal projectors drawn from the corresponding points in the elevation ; nearly all of these are shown, and, if dealt with one point at a time, following each through its several positions, the necessary data for drawing the curves will be obtained without great difficulty.
It will be seen that, to avoid a confusing mass of lines, the same projector has been used upon several arrises, but it must be noted that, it is necessary to project into the plan the new points where the horizontal projector intersects the arris in question, and, to simplify the procedure, it is best to deal with one arris at a time and not to copy off all the projectors shown on the plate straight away, as this is given in its completed state, with all the construction lines upon it. In the usual way many of these lines would have been removed after serving their purpose, leaving the drawing clear for subsequent projectors.
To obtain the Soffit Mould Fig. 5.—This figure is drawn to half the scale of Fig. 1, for the purpose of placing it on the same page, but in the reproduction must be drawn to the same scale as the rest of the drawing. The drawing shows the mould for the soffit of the frame, but the method will be the same for obtaining that of the lining and the architrave, also edge of the ground.
A-a-b is the plan of the cone formed by the radiating jambs ; the semicircle is the elevation of its end laid down or rebated into the horizontal plane. Divide the semicircle into a number of equal parts as shown, project these points to a--b, then carry them to the apex A, as shown ; next describe the development of the edge of the semi-cone. With A as centre and A-a as radius, describe the arc a-12. Make this equ;d in length to the semicircle a--6-b by stepping around same with the compasses and transferring a like number of steps to the development, the greater the number the greater the accuracy of the length obtained. Then transfer in a similar manner the numbered points 1 to 11. Draw lines from them to the apex A. The triangle then obtained will be the shape of the covering or " envelope "
Was this article helpful?