22 



BELL SYSTEM TECHNICAL JOURNAL 



pressing, forging or upsetting to o])tain definite bonding of the component 

 parts were found to be superior to those made by brazing, puddUng, or 

 casting. High-strength metals processed with the proper technique to 

 effect good metal flow and alloying bonding are preferable. The interface 

 of the stone and metal should be free from porosity and crevices. Figure 2 

 depicts a defective mounting due to poor metal flow which caused the early 

 breakage of the stone. 



Contour of the Die Hole 



The contour of the die hole is shown in Fig. 1. It is the familiar radial 

 or parabolic t>-pe which is commonly used in the copper wire industry with 



Fig. 1 — Contour of the die hole 



good results. The straight angles associated with cemented carbide dies do 

 not exist in the present day commercial diamond dies. The noted angles 

 are arcs and the values cited refer to the average chords subtending these 

 arcs. In agreement with the findings of comparatively recent English 

 investigations^ of the theoretical factors afifecting wire die performance, it 

 was found that small changes of angle do not appreciably influence the die 

 pull. Whatever differences do exist are blanketed out by changes in the die 

 frictional forces. The permissible variations in angle are consistent with 

 the average found in today's best commercial dies. In recutting dies ob- 



