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Popular Science Monihly 



ventilator, or to give sizes, as it would 

 complicate the drawing and confuse the 

 student. Allowance must be made on the 

 patterns for all seams and wiring. 



Laying out a pattern for cutting a hole in 

 the roof for insertion of the ventilator base 



A very interesting and simple problem 

 that is not generally known among sheet 

 metal workers is shown in Fig. 2. If, 

 when making the ventilator shown in 

 Fig. 1, it is desired to obtain the pattern 

 for the hole in the roof, the method is as 

 follows: First, draw view A with the 

 full bottom view as shown by the circle. 

 Second, divide the circle into sixteen 

 parts, and project the points to the base 

 line. From where they cross the base 

 line, run the lines up to the apex C exactly 



where on these lines, draw the center 

 line 1-9 parallel to the roof line. Notice 

 that now we have the exact length 

 of the hole and the exact location of 

 each radial line. If we can now get 

 the exact width on each of these lines, 

 we shall have our pattern. We can 

 get these widths by drawing a front 

 view. Make the drawing the same 

 as for the side view except that the roof 

 line is omitted. Notice particularly that 

 the numbers on the bottom view circle 

 have been turned one-quarter circle to 

 the right, although on the ventilator they 

 are, of course, in the same place. For in- 

 stance, 1 is the highest point and 9 is the 

 lowest point on both views. Fourth from 

 view A, where the radial lines cross the 

 roci line, run lines to the front view B. 

 Make a cross where these lines intersect, 

 the same numbered lines coming up from 

 the bottom view circle. Connect these 

 crosses with a curve and you will have a 

 true front view of the joint between the 

 ventilator and the roof. It is understood 

 that the upper part of the oval would be 

 back of the ventilator and therefore in- 

 visible from the front. Sixth, to transfer 

 these widths to the pattern, place one 

 point of the compasses on center line, and 

 find the width of 2-16, then lay this off on 

 the 2-16 line of the pattern. Transfer all 

 the other widths in the same way, connect 

 the crosses with a curve and you will have 



as was done in the preceding 

 problems. Third, from 

 the points where these radial 

 lines intersect the roof line, 

 draw lines at exact right 

 angles, as shown in the draw- 

 ing. Number these lines, 

 giving them the numbers at 

 the bottom view points from 

 which they started. Any- 



Fig. 3: Pattern 

 layout for making 

 the three parts of 

 the ordinary scale 

 scoop. Two of the 

 pieces are parts of a 

 cone while the other 

 is a plain cylinder 



the exact pattern for 

 the roof hole. 



In Fig. 3 the "scale 

 scoop," we have an 

 interesting and ap- 

 parently difficult 

 problem, but one 

 which is much easier 

 than it looks. This 

 scoop is circular in 



