Page:Popular Science Monthly Volume 92.djvu/793

 Popular Science Monllihj

��The "boss" on the inside of the handle is part of a cylinder so it must be devel- oped by parallel lines just as we developed the elbows and tees in previous issues. In this pattern we use the same prin- ciples as in Fig. 1. First, from the front view project lines upward and draw the section view M, obtaining the width from the other view of the handle marked A^ Second, divide the section circle of the boss into four parts. Project points 2 and 4 down to the front view of the boss. From where these lines cross the handle, draw lines at right angles. Draw the line 0-P. Now we have the true length of the pattern. We can get the true widths from the sections view, measuring off four of the section spaces on line 1-5 on the pattern and two on line 2-4 of the pattern, do the same with the lower half, connect these points with a curved line and the pattern for the handle boss is complete.

The pattern for the handle is a new ap- plication of some previously demonstrated principles in parallel lines. First draw the view N. Second, divide the outline of the handle into any number of spaces as shown by the crosses. Project these points across to view N. Number them as shown. Third, draw the center line of the pattern, get the correct length by measuring with compasses the spaces on the outline of the handle and transferring them to the center line of the pattern. Be sure to give each point the same num- ber on the pattern as it has on the other views. Fourth, project lines up to the pattern from the points on the TV view of the handle. Make crosses where these lines cross the same numbered line on the pattern. Join the crosses with a free hand curve and the pattern for the handle will be complete.

A simple problem that is often con- fusing to the ordinary sheet metal worker is illustrated by Fig. 3. The problem is that of developing the patterns for a ninety-degree tapered elbow of any num- ber of pieces. This elbow has six pieces and the small diameter is one-third that of the large diameter. These patterns may also be used for a ship's ventilator, although this type of ventilator should not be confused with the regular oval ventilator which is developed by "tri- angulation." This method will be ex- plained later in the series.

��777

Each section of the tapered elbow is part of a cone as can be seen in drawing L. To develop the patterns: First, draw a cone, the base of which is equal to the diameter of the large end of the elbow. Second, on the upper part of the cone draw the line for the small diameter of the elbow. The altitude of the cone may be varied to suit the length of elbow re- quired. Third, we must now obtain the miter lines. This is done in exactly the same manner as explained in the October 1917 issue for ninety degree cylindrical elbows. The rule given there is: "In all elbows of more than two pieces, the two end sections should be one-half the size of the other sections." In this case,

��Patter

��^^

�"S^^^r^^i^U^^

�/

�^-^^^W

�^

� � � �■Ls^jis^c

�"^

�t J

�^

�\

� �^^^.

� �s

�^

�/

�V

�V

� �>

� � �\

�, /

� �^^d

�5 A

�f

� �fig 4

� � �Pitttern

� � �^

�^

�2

� � �5 '

�^ 5

�9

�' {

�) 1

��A pattern for another type of a ninety- degree reducer elbow used for a ventilator

there are six sections to the elbow so the four middle sections will each have twice the number of angles in it as the end section. This is shown in drawing K which illustrates the use of a "protractor" which is a small brass "angle measure" and can be bought for 25 cents. The crosses indicate the miter lines. Note that the two end sections have only 9 deg. each, while the middle sections have 18 deg. each. Take the diameter of the cone base and lay it off as N-0 on the drawing K. This will give the exact shape of section A on the cone. Lay this off as section A on the cone. Take the distance on the center line of section A and set off the same distance on the center line for section F, then divide the remainder of the center line into four equal spaces. Draw the miter lines at an angle of 9 deg. to the line M which is

�� �