Essentials of Sheet Metal Work and Pattern Drafting by James Sharkey Daugherty

Author:James Sharkey Daugherty
Language: eng
Format: epub
Publisher: F. J. Drake & co
Published: 1918-03-25T05:00:00+00:00

Figure 93.—Pattern for a Hexagonal Pyramid.

spaces on the stretch-out arc, and complete the pattern in the same manner as shown in the preceding problem.

Patterns for these problems should be developed, and models made from sheet metgil, thus giving practice in construction. These models will at once show any error in the pattern which might otherwise be overlooked.

Rectangular Pitched Cover. —Sheet metal workers are frequently required to construct ornaments in cornice work, a hood, canopy, or a cover for to article square or rectangular in form. These articles are usually made in the form of a square or rectangular pyramid having a short height or rise to the apex.

. Patterns for work of this kind are usually laid out directly on the metal by a short method in which no elevation is required, as the true length of the radius for describing the stretch-out arc is found in the plan. Figure 94 shows the development of a pattern for a rectangular pitched cover by this method.-

The half elevation and section can be omitted. They were drawn in this case to show the construction and method of connecting the hoop B to the cover shown at A. The hoop is a strip of metal of the required width, having a single hem on the lower edge and an edge turned to a right angle on the upper side for seaming, as shown in the section.

The length, width and height of cover being known, first draw a plan to the required size, as shown by 1-2-3-4. Next draw the diagonal lines intersecting in the center at m, which lines represent the hips of the pitched cover in plan. Bisect the line 1-2 and locate the point x, then draw a line from x to the center m, showing the position of the seam. Before describing the stretch-out arc for the pattern, find the true length of one of the hip lines in the plan and use that dimension as the radius for describing the stretch-out.

To find the radius, draw the line m-o at right angles to the hip line m-3 in the plan. The height of the cover as shown by ad in the elevation is marked on the line m-o at

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