FLEXIBLE REPEATER MANUFACTURE 115 



Only one supplier was willing to accept orders for the tubes, and only 

 on the basis of meeting the mechanical requirements on the outside sur- 

 face. To establish a source of supply, it was necessary to accept the sup- 

 plier's proposal on the basis that some of the tubes produced could be 

 expected to meet requirements on the inside as well as the outside sur- 

 face. Inspection of the inside surface was performed with a 10-foot Bore- 

 scope. 



The supplier then set aside, overhauled, and cleaned a complete group 

 of drawing facilities for this project. In addition, a number of refinements 

 were made in lubrication and systematic maintenance of tools. After all 

 refinements were made and precautions taken, however, the yield of 

 good tubes in the first 400 produced was less than 1.0 per cent. Consulta- 

 tions with Western and Bell Laboratories' engineers, and with the sup- 

 plier's cooperation, raised the yield to approximately 50 per cent. 



Procurement of satisfactory mica laminations for capacitors intro- 

 duced an unusual problem. The best grade of mica available in the world 

 market was purchased which the supplier, under special plant condi- 

 tions, split and processed into laminations. Despite care in selection and 

 processing, only 50 per cent of the 250,000 laminations purchased met 

 the extremely rigid recjuirements for microscopic inclusions and delam- 

 inations, and less than 8 per cent survived the capacitor manufacturing 

 processes. 



A large number of the parts, and the most complex, are made from 

 methyl-methacrylate (Plexiglass). At the time manufacture began, there 

 was little, if anj^, experience or information available on machining this 

 material to the required close tolerances and surface finish. Consequently, 

 considerable pioneering effort was expended in this field before satis- 

 factory results were obtained. 



The methacrylate parts cover a wide range of size and complexitj^ — 

 from l|-inch diameter by 4|-inch long tubular housing to tiny spools 

 |-inch diameter and j^-inch long. Most of the parts are cylindrical in 

 shape with some semicylindrical sections that must mate with other 

 sections to form complete cylinders. Others have thin fins, walls, flanges 

 and projections. Five representative parts are shown in Fig. 2. 



Methyl-methacrylate has a tendency to chip if tools are not kept sharp 

 and care is not used in entry or exit of the tool in the work, particularly 

 in milling. In some cases, it is necessary, with end-milling, to work the 

 cutter around the periphery of the area for a slight depth so that sub- 

 sequent cuts will not break out at an unsupported area. Normall}^, with 

 a sharp cutter and a 0.010-inch finish cut, and a slow feed, chipping will 

 not result. High-speed steel tools with zero rake were used for turning 



