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BELL SYSTEM TECHNICAL JOURNAL 



be approximately 0.001 in. -lb. This constant value was subtracted 

 from the other measured values of torque. The resulting values of 

 free spring torque are plotted as a function of the number of turns in 

 Fig. 6. The torque values calculated by eciuations (4) and (19) and 



2 3 4 5 

 TURNS OF SPRING ON ARBOR 



Fig. 6 — Dependence of torque on the number of turns of the spring engaging the arbor. 



using the value oi ix — 0.165 obtained as described in the next section, 

 are shown on the curve to indicate the agreement. 



Experimental Check of the Holding-Torque Relation 



It is to be expected that any relation for which the coefficient of 

 friction is a controlling factor will be difficult to check accurately. 

 Equation (8) for the slipping torque is of this type. It is possible 

 however by taking a large number of measurements to establish the 



