In Fig. 371 is shown a top and side view of a boss whose sides are in part parallel and just sufficiently apart to allow the faucet to fit between them. L N represents the diameter of the opening at the top. K L M N represents the general shape of the boss where it joins the can and is the result of the conditions existing in the side view, but is not made use of in the process of obtaining the pattern. The essential points are the curve of the can body, D ABE, the diameter of boss at top, L O N, the distance between D and E and the distance X C, all of which are shown in the side view.
Divide one-quarter of the plan of the top, as indicated by O N, into any convenient number of spaces, as indicated by 1, 2, 3, etc. From the points thus established drop lines vertically, cutting the line representing the top in the side view, as shown from F to G. From the points thus established in F C carry lines parallel to the side F D, producing them until they cut the curved line D A B E, as shown between D and A. The next step to be taken is to obtain the profile which would be shown by a section taken through the article at right angles to the line D F. For this purpose at any convenient point draw a line through D F and at right angles to it, as shown by P R. From the points established in the plan of the top, as shown from O to N, carry lines vertically until they meet the horizontal line K M passing through the cen1ter of the top, as shown. Taking the length of each of the distances thus obtained in the dividers, set it off from either side of P R on the lines of corresponding numbers, and through the points thus obtained trace the curve, as shown. Then this curve will represent the required section from which the stretchout of the envelope may be obtained. On the line R P, produced sufficiently outside of the side view for the purpose, lay off the stretchout of one-half of this curve, as shown, and through the points thus established draw measuring lines parallel to D F. Then, with the T-square placed parallel to P R, or, what is the same, at right angles to D F, and brought successively against the points in the profile of the can body between D and A, cut the measuring lines of corresponding numbers. In like manner bring the T-square against the points in the top of the article shown from E to C and cut the measuring lines of corresponding numbers. Then lines traced through the points thus obtained, as shown by D' A' and F' C, will be one-half of the pattern of one of the ends. As that portion of the boss lying between points A, B and C is simply a flat triangular piece it is only necessary to add a duplicate of its shape to that part of the pattern just obtained, bringing one of its straight sides against the line 5, all as shown. To the other straight side C' B' must be added a duplicate of the first part of the pattern reversed, as shown by B' C G' E'; the resulting shape will then constitute the pattern of one-half the boss.
Fig. 371. - Pattern for a Can Boss to Fit Around a Faucet.