THE SPRING CLUTCH 



731 



of friction for this number of turns a measurement was made before 

 and after oiling the arbor and spring with a Hght lubricating oil. 

 There was a decrease in torque of approximately 0.25 per cent. 



The inside diameter of the spring as measured by a taper gage was 

 0.180 in. ± 0.001 in. The torque for arbors ranging in size from 0.182 

 to 0.193 in. was determined and is shown in Fig. 5. This curve ex- 



Z 0.008 



^ 0.005 



0.6 O 



0.180 0.182 0.184 0.186 0.188 0.190 0.192 0.194 



DIAMETER OF ARBOR IN INCHES 



Fig. 5 — The free torque and the radial force on the arbor for a phosphor-bronze 

 spring on arbors of different diameters. 



trapolated to zero torque gives, for an accurate measure of the inside 

 diameter of the spring, 0.1794 in. Using this value and the quantity 

 £/, determined by obtaining the resonant frequency of a straight short 

 length of the ribbon, of which the spring was made, vibrating as a 

 fixed free reed, the radial force on the arbor as calculated by equation 

 (19) is shown by the dotted curve as a function of the arbor diameter 

 Iri. The points indicate values of /o obtained from the measured 

 values of torque by the use of equation (5). The two sets of values 

 agree within about 2 per cent. 



As a further check on the validity of the calculations under practical 

 conditions, the free torque of a phosphor-bronze spring on a dial- 

 governor arbor was measured for various numbers of I urns of the 

 spring engaging on the slipping arbor. The torque due lo bearing 

 friction alone with no spring in place was also measured and found to 



