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 



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 



