Page:Sheet Metal Drafting.djvu/48

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19. The Half-pint Cup.—This problem is intended to bring out the method of notching employed when a wire is rolled into a cylinder, to describe the standard "tin lock," and to show how a bottom is snapped on.

In drawing the elevation of the half-pint cup, special attention should be given to the following items: The lines representing the wire must be in. apart. The lines at the bottom must be ⅛ in. apart. The handle must be drawn according to the dimensions given in Fig. 49. The profile is located by dropping extension lines from the elevation. At a distance of 1¾ in. from the lower line of the elevation, the horizontal center line of the profile should be drawn. The extension lines dropped from the elevation should intersect the center line, thereby setting off the horizontal diameter of the profile. The profile is drawn with the compass after the center of this diameter is located. The handle of the cup is shown attached to the profile, but it is not essential that this be drawn, since the pattern of the handle is a regular taper from a width of ½ in. at the top to ¼ in. at the lower end.

The profile is divided into equal spaces and each division numbered. After the line of stretchout is drawn, the spacing of the profile is transferred to this line and the divisions numbered to correspond. At the points 1 and 1 of the line of stretchout perpendicular lines are erected. The stretchout is finished by extension lines carried over from the elevation. The wire edge which must be computed is added to the top edge of the stretch-out. A ¼-inch edge is added to each side for a standard "tin lock." Since a lock has three thicknesses the full allowance is never turned. For a tin lock in. must be turned in a bar folder. The notching of the wire edge in Figs. 50 and 51 never goes in as far as the circumference line, and always goes down below the top line of the stretchout a distance equal to the diameter of the wire. This notch removes the thick seam on the body at the point where the wire crosses. The bottom of the lock is notched as shown in Fig. 51.

The pattern of the bottom of the cup is drawn by first reproducing the profile and adding a ⅛-inch edge all around. This edge