THE L3 SYSTEM — QUALITY CONTROL IN MANUFACTURE 983 



During the initial period of manufacture of these inductors, it was 

 found that the seriousness of the variations in inductance, contributed 

 by the mre diameter tolerance, could be minimized by selection of the 

 mre stock. Experience has indicated that because of the small amount 

 of wire used per coil, this procedure can be followed without undue losses. 



The variations contributed by the core diameter tolerance have been 

 minimized by the introduction of a ground core having a diameter tol- 

 erance of =b0.0002". By virtue of the manufacturing methods introduced 

 by the core manufacturer to meet this close diameter tolerance, a fairly 

 normal distribution of the core diameter was obtained. 



In addition to the variables due to the material used for these coils 

 there were substantial variations in inductance inherent in the winding 

 machines and operator ^vinding techniques particularly in the attach- 

 ment of the wire to the terminals. Early control charts showed an erratic 



Fig. 7 — A shadowgraph of a coil winding showing irregularities in the wire 

 spacing due to non-uniformity in pitch control of winding machine. 



variation of inductance which was traced chiefly to backlash in the 

 winding machine. 



Fig. 7 is a shadowgraph of the coil winding showing the irregularities 

 in the wire spacing due to non-uniformity in the pitch control of the 

 winding machine. In addition to this variation, trouble was experienced 

 in maintaining pitch control at the end of the winding due to the neces- 

 sity of sanding the lead before splicing to the terminal. This latter varia- 

 tion wsLS brought under control by the introduction of a type of wire 

 which can be soldered to the terminal without mechanically removing 

 the insulation, thus avoiding the loss of the winding machine accuracy 

 of spacing and tension. After numerous machine modifications, satis- 

 factory control of the mnding pitch has been obtained so that with 

 normal variations, the inductance of the coils is within the distribution 

 requirements of the specification. This uniformity of winding is illus- 

 trated in the shadow^graph in Fig. 8, which is a typical example of current 

 product. The type of machine modifications required to produce this 

 improvement in product control included the foUomng: 



