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BELL SYSTEM TECHNICAL JOURNAL 



to excessive cost. For the wire sizes smaller than No. 16 down to as 

 fine as No. 42 B. & S., diamond dies as described below are used. 



Fig. 20 



Diamond Die Study 

 It was necessary to make an extensive study of the manufacture of 

 diamond dies because dies through which wire could be satisfactorily 

 drawn at low speeds failed to draw to gauge and without excessive 

 breakage of the wire as the speeds were increased. At this time 

 practically all commercial diamond drilling was done in Europe, 

 Belgium being the hub of the diamond cutting industry, and the art 

 was new to this country. The diamonds generally used for wire draw- 

 ing dies are obtained from South Africa,^ Australia, and Brazil, and 

 made into diamond dies in Europe. 



* The South African and Australian diamonds are the more suitable for wire 

 drawing. There are two types of the former, the smooth brown premier which is not 

 suitable for dies because of its tendency to crack and split, the other commonly known 

 as the Jager, a product of the Jagerfontein mines. These stones, very irregular in 

 contour and light gray to black in color, are most suitable for dies. The Australian 

 diamonds are gray to brown to almost black in color and can be distinguished from the 

 Jager. Many of the Brazilian diamonds are a dark gray similar to graphite in color 

 and not being translucent are dilificult to inspect for seams, cracks or inclusions. 



