116 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 







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Fig. 2 — Methyl methacrj'late parts. 



and boring operations. Standard high-speed milling cutters and end 

 mills were used for milling except for the cutting edges, which are honed 

 to a fine finish. A clearance angle of 7 degrees for milling and 10 degrees 

 to 15 degrees for lathe work was found most satisfactory. In lathe work, 

 the general rule was light feeds (0.003 inch-0.005 inch) and small depth 

 of cut. However, the depth of cut could be safely varied over a wide 

 range depending upon many factors, such as type of part, quality of 

 finish, machine and tool rigidity, effective application of coolant, and 

 tooling to support and clamp the part. In one operation of boring a 

 li^-inch diameter by 4|-inch deep blind hole within ±0.002 inch, the 

 boring terminates in simultaneously facing the bottom of the hole square 

 with its axis. A cut ^f-iiich deep with a light feed was taken with a spe- 

 cially designed boring tool with the coolant being fed through the shank 

 to the cutting edge. All completely machined parts were annealed for 

 12 hours at 175° F. 



HIGHLIGHTS IN ASSEMBLY AND BRAZING 



Repeater units are encased in hardened steel rings which previously 

 had been tested at 10,000 pounds per square inch hydraulic pressure. 

 This pressure is approximately 50 per cent higher than the greatest pres- 

 sure expected at ocean bottom. The steel rings were encased in a copper 

 sheath and closed at each end with a glass-to-Kovar seal, with the cen- 

 tral conductor coming through the glass to the outside. The copper sheath 

 was then shrunk to the steel rings and glass seals using 6000 pounds per 



