108 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



The situation attending the manufacture of a relatively small number 

 of comparatively large copper parts used in the rubber and core tube 

 seals was much the same. Here, again, the large size machine tools and 

 additional manufacturing space, required for only a short time, would 

 have increased the over-all cost of the project considerably. These parts, 

 therefore, were subcontracted in the local area and inspection was per- 

 formed by Hillside inspectors. 



A safeguard, in so far as integrity is concerned, was provided by the 

 fact that these were individual parts that could be reinspected at the 

 time of delivery. No subassembly operations that might possibly result 

 in oversight of a defect, were subcontracted. 



Manufacturing Conditions 



Two major problems confronted us in planning the manufacture of 

 repeaters. First, to produce units that were essentially perfect; and 

 second, to prevent the contamination of the product b}^ any substance 

 that might degrade its performance over a long period of time. In ap- 

 proaching both of these objectives, it was realized that the product had 

 a definite economic value which the cost of production should not 

 exceed. In many cases, therefore, it was necessary to rely on judgment, 

 backed by considerable manufacturing experience, in determining when 

 the "point of no return" had been reached in refining processes and 

 practices. 



The initial approach to this phase of the job was to classify, with the 

 collaboration of Bell Telephone Laboratories, all of the manufacturing 

 operations involved as to the degree of cleanliness required. In setting 

 up these criteria, it was necessary to evaluate the importance of contami- 

 nation in each area and the practicability of eliminating it at the source 

 or to insure that whatever foreign material accumulated on the product 

 was removed. 



A representative case is the machining of piece parts. While the shop 

 area is cleaner, perhaps, than any similar area in industry, the \evy 

 nature of the work is such that immediate contamination cannot be 

 avoided since material is being removed in the form of chips and turn- 

 ings, and a water soluble oil is used as a coolant. In this instance, however, 

 the parts can be thoroughly cleaned and their condition observed before 

 leaving the area. Conversely, in the case of an operation such as the 

 assembly of paper capacitors into a container which is then hermetically 

 sealed, it is vitally necessary to insure that both the manufacturing 



