490 BELL SYSTEM TECHNICAL JOURNAL 



rich surface and does not detract from the appearance of the handset. 

 Automatic grooving machines were developed for this purpose. Figure 

 4 shows a grooved handset handle. 



It has been found necessary to pay close attention to the design in 

 order that die parting lines, ejector pin marks, gate marks and the like 

 will appear at points where they may be readily eliminated by simple 

 trimming and grooving operations, or where they may be left without 

 objection to appearance or function of the part. 



Fig. 4 — Grooved handset handle. 



General Test Methods and Requirements 



The most satisfactory test is one that can be applied to the finished 

 part to measure the ability of that part to perform its function satis- 

 factorily in service. This ideal is seldom realized, not only because of 

 the difiiculty of defining the service requirements but of finding tests 

 that are wholly representative of service conditions. It is customary, 

 therefore, to apply a series of tests whose sum total will approach the 

 ideal as nearly as practicable. Molded organic plastic parts are 

 different from parts made from most other materials in that the 

 molding process may modify them and render them quite different 

 from the raw material. In the case of thermosetting compounds 

 this is particularly true. 



Tests are in the main applied, therefore, to a molded part of repre- 

 sentative specimen of the fabricated material. In the telephone plant 

 the items that are of most importance are strength, both transverse 

 and impact, permanence of form, appearance, effect of moisture and 

 drying on swelling and shrinkage, insulation resistance, electrical 

 breakdown potential, and reaction on adjacent materials. Methods 



