To Describe A Pattern For A Tapering Elbow

Let AB and CD, fig. 71, equal large end of elbow, DHB the angle; make HF equal CG, and EP equal AB; make JK equal the small end of the elbow; draw the lines BK and AJ, continue the lines until they intersect at I; describe the semicircles AB and JK; divide the semicircles into the same number of equal parts; from the points draw lines, as 1, 2, 3, etc.

On any line, as AB, fig. 72, with the radii IK and IB; describe the arcs HI and CD; set off CAD equal in length to the circumference of the large end AB; draw the lines CB and DB; set off on each side of AB the same number of equal distances as in the semicircle AB; from the points draw lines cutting the centre at B; make AE equal to BL; make CF and DG equal to AM; also each of the lines bearing the same figure as 1, 1, 2, 2, 3, 3, etc., then a line traced through the points will form the pattern.

Edges to be allowed.

Fig. 71.

Fig. 72.

Boiler Cover

Fig 78. To describe an Oval Boiler Cover.

Erect the line DC; make FD equal to one-half the length of the boiler bottom before the edge is turned; describe the circle HDI one-eight of an inch larger in diameter than the breadth of the bottom; let FG be three-eights of an inch; then apply the corner of the square on the line AB, allowing the blade to cut the circle at I and the tongue at the point G; draw the lines GB, BH, also the lines GA, AH; allow one-eight of an inch for an edge, as shown by the dotted lines, the cover will be the same size as the bottom or pit.

Flange

Fig 74. To describe a Pattern for a Flange for a Pipe that goes on the Hoof of a Building, as fig. 59.

Fig. 75.

Let ABC, fig. 74, be the pitch of the roof; make DE equal to the diameter of the pipe; describe the circle FG; make FG the Same in diameter as the pipe; draw the line FG; set off on the line FG any number of equal parts; from the points draw lines at right angle to FG as 1, 2, etc.

Fig. 76.

Set off the line HI, fig. 76, equal in length to DBE in fig. 74; set off on the line HI the same number of equal parts as in the line FG; from the points draw lines at right angle to HI; set off on each side of HI the same distance as on each side of the line FG in fig. 75, as 1, 1, 2, 2, etc.; a line traced through the points will form the piece to be cut out; when there is to be an edge turned up, it must be allowed inside of the line traced. The same rule is applied to describe a pattern for a flange for fig. 57; make HI, fig. 76, equal BF, fig. 57, then proceed the same as described above.