In Fig. 370 D F K H E shows a front view, V L M O a side view, and A C B a plan of a blower. The conditions which determine the course to be pursued in arriving at the pattern are that its upper outline shall conform to the semicircle F K H of the elevation, and that it shall slant from K to G at an angle indicated by the line L M of the profile. Therefore, the first step will be to determine a true section of its upper portion or hood upon a line at right angles to L M from the point N of the side view; after which, with N M and N L as miter lines, the pattern can be developed in the usual manner. To obtain a true profile of the hood, divide one-half of the semicircle F K H into any number of equal spaces, and carry lines from each of the several points to the vertical line L N of the side view. From the points thus obtained in L N carry lines parallel with L M indefinitely, which intersect at right angles by the line T S, located at any convenient point outside of the diagram. With the dividers take the horizontal distances between the points in the arc F K to the line K G, and set them off on the lines of corresponding number, measuring from the line T S. Then a line drawn through the points thus obtained, and as indicated by T R, will be a correct section through the inclined portion of the blower. Take the stretchout of the profile T R point by point and place the spaces on the line U V, which is drawn at right angles to L M. Through the points in U V draw the usual measuring lines at right angles to it. As the points from the profile T R have already been dropped upon both the miter lines M N and N L, it is only necessary to carry them, at right angles to L M, on to the measuring lines of corresponding numbers. Then a line traced through the points thus obtained, and as indicated by F1 K1 H1, will be the desired pattern.
Fig. 370. - Pattern for a Blower for a Grate.