SOME CERAMIC MANUFACTURING DEVELOPMENTS 279 



This development permitted the manufacture of ceramic insulators 

 within limits not feasible with other methods of manufacture at that 

 time except by machining from mineral talc and to closer dimensional 

 tolerances than ever before attained in molded ceramic parts. The 

 cost of the parts was reduced to a fraction of that of machined parts 

 and their quality was greatly improved. Since that time the process 

 has been used in the manufacture of other close tolerance ceramic 

 parts for telephone use such as the insulator shown in the upper part 

 of Fig. 8. 



Although the outline of miscellaneous manufacturing developments 

 given herein does not include all of the engineering development 

 effort on glass, porcelain and vitreous enamel problems it gives a 

 general picture of the type and scope of past engineering work in the 

 production of ceramic articles for telephone apparatus. The miscel- 

 laneous ceramic parts used in telephone apparatus were described in 

 an earlier publication.^^ 



12 A. G. Johnson and L. I. Shaw, "Ceramics in the Telephone," Industrial and 

 Engineering Chemistry, Vol. 27, pp. 1326-1332, November, 1935. 



