beginning of the machining operation grave doubts existed whether pentagons 

 could be machined to the dimensional tolerances specified (Appendix A) for 

 the prototype 66-inch sphere, they soon were dispelled by these dimensional 

 checks: the dimensional tolerances specified could be maintained. After the 

 dimensions were checked, the large spherical pentagons were placed into con- 

 toured, padded plywood boxes (Figure 36); the model pentagons were stacked 

 in shop baskets. 



Figure 31 . Sawing spherical sectors into rough spherical pentagon shape 

 for the 66-inch-diameter capsule. 



Annealing. No annealing of the model pentagons was performed after 

 machining, as there were no contoured boxes or portable molds to support 

 them during annealing. The annealing of the model pentagons was performed 

 only after complete assembly and bonding of the model spheres, when the 

 individual spherical pentagons could not readily change their curvature. 



Large-scale spherical pentagons with a 33-inch spherical radius were 

 annealed after completion of all the machining operations. This was per- 

 formed to decrease the residual stresses introduced into the acrylic plastic 

 by thermoforming, bandsawing, and milling. It was hoped that the decrease, 

 if not complete elimination, of tensile stresses on the acrylic plastic surfaces 

 would eliminate the tendency of acrylic plastic to craze on the machined 

 surfaces. 



59 



