860 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



i.e. 2%-inches from its anchorage point in the phenol resin block. This 

 degree of straightness is satisfactory also for the automatic manufacture 

 of relay combs in which a multiplicity of straightened wires are guided 

 into a molding die and positioned so accurately that they can be per- 

 manently imbedded in phenolic resin to the close dimensional limits 

 necessary for ultimate assembly into relays. 



EXPERIMENTAL WORK 



Wire Straightening 



The original experimental work on wire straightening was done at 

 the Bell Telephone Laboratories to aid in establishing the feasibility 

 of a wire spring relay design. After eliminating other approaches it was 

 decided to straighten the wdre in a motor-driven machine by pushing the 

 wire through carefully oriented dies in a rotating head. The mre pro- 

 duced in this manner was known to have a twist but was adequate for 

 making model parts. Subsequently, Western Electric development 

 engineers made a survey of available commercial \\dre straightening ma- 

 chines. A machine was purchased which, while not intended for straight- 

 ening \vire of the small diameters used in wire spring relays, was capable 

 of modification. Among the important things learned from the operation 

 of this machine were first, it is preferable to push instead of pull wire 

 through the rotating die head because of interference at the puller due 

 to twist in the straightened wire; second, much of the twist can be re- 

 moved from the straightened mre by spinning the spool of raw mre 

 counter to the direction of the driven die head; and third, it appeared 

 that a simpler approach than spinning the. spool of raw wire would be 

 to pass the ^vire through a second straightening head rotated in the op- 

 posite direction from the first. On the basis of these observations, a 

 Hawthorne-designed experimental straightening machine was con- 

 structed. This machine featured two die heads independent of each other 

 and counter rotating in operation. Five individual sets of die blocks, 

 wth provision for spacing adjustment as found on the rotary die holder 

 of the commercial straightener, were retained in each head. Subsequently, 

 this experimental machine was used for an extended series of tests to 

 determine such things as the optimum spacing between individual dies, 

 the proper offset from the center line of the head for each die, the best 

 ratio of opposing head speeds, and the maximum rate of mre feed with 

 respect to the rotational speed of the die holder head required to produce 

 straight wire in the diameters employed in the mre spring relay. 



Since it had become evident by the time this study was well advanced 



