140 



HANDBOOK OF MECHANICAL DESIGN 



GRAPHICAL SOLUTION OF HELICAL SPRING FORMULAS 



F= Inches Deflection per Turn at Stress Indicated 

 0,21 0.18 0,15 0.12 0.10 0,09 0,06 

 J I i__l . I \ I 1 I ■ ^-^'f I I L 



90,000^ 

 75,000 b 



6Q000 



60,000 



75,000 



-125,000 '^ 



100 110 120125 



■I \ ' 9Q000 



90' 100 110 120 130 140 150 

 Pounds Tension or Compression Load on the Spring at Maximum Unit Stresses Indicated 



This chart, developed by Carl P. Nachod, of Nachod & United States Signal Co., 

 can be used for the solution of the formulas for round-wire hehcal springs given on the 

 preceding pages. The chart is based on G being 11,500,000. The Wahl factor is 

 incorporated in the equation on which this chart is based. 



To use the chart: Given a load P of 20.1 lb. and an allowable stress of 60,000 lb. 

 per sq. in.; go vertically upward from the point representing 20.1 lb. on the lower 

 60,000 scale to the intersection Avith the load ray, extending upward to the right, corre- 

 sponding to the spring index (D/d) selected, in this example r = 8. A horizontal line 

 through the intersection point to the scale for wire diameters gives d = 0.09 in. 

 Extend this horizontal line to the- right to the "deflection" ray r = 8 of the group of 

 rays extending upward to the left. From this point, trace vertically upward to the 

 F scale corresponding to the value of S selected, and this gives the deflection F as 

 0.079 in. per turn at 60,000 lb. per sq. in. stress. 



