Page:Popular Science Monthly Volume 92.djvu/155

 Simple Designs for Sheet Metal Working

VIII. — Off-center tee joints, any angle, any shape By Arthur F. Payne

Former Director of Vocational Education, Columbia University

��THE four problems in pattern de- velopment presented in this article will seem really difficult for the beginner; but those who have worked out the preceding problems, especially those of the last article, will find these easy. They merely require careful work; the methods of working are practically the same as for the preceding problems. Only two new steps in pattern development will be demonstrated.

The method of developing the patterns for the two square pipes intersecting at an angle of 60 deg. off center is shown in Fig. 1. The steps taken are as follows: Draw the front view, A, laying out the required angle as explained in last month's article; draw the bottom view of the small pipe B; number the four corners as indicated; draw the end view C; draw the bottom of the small pipe D of the end view and number the corners as shown, taking care to keep the numbers in the proper relation to the front view. Notice that the pipe has been turned, for this afifects the position of the numbers.

���Method of developing patterns for two square pipes intersecting at an angle

A new step in pattern drafting must be learned before we can develop the pattern for the small pipe. The front

��view A must be completed by showing exactly the shape of the joint where the two pipes come together. This is done in the following manner: Place a pencil on the point 4 on the bottom of the end view; follow the line upward until it touches the large pipe, then run the line

���This problem is a little more complicated but is worked out in the usual manner

over to the front view A until it crosses the line coming up from point 4 on the bottom of the front view. Make a cross where these two numbered lines cross each other. Do the same with the other three numbers. Connect the four crosses with straight lines, and you will have an exact drawing of the joint. Notice that the two lower lines of this joint are drawn in dotted lines. This is to show that if the joint is made in metal these lines will not be seen because they will be back of the small pipe.

To develop the pattern for the small pipe, proceed in the usual manner as ex- plained in previous chapters. Draw the base line E — F, transfer the distances from the bottom view to get the correct length, extend the lengths of the pipe from the front view until similarly numbered lines cross each other, one line coming up from the base line and the other coming across from the front view.

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