. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . he core were cylindrical, a standard core could notbe used, for the two end portions which fit into the coreprint depressions must be molded and baked with thebody. In this case, a half core box may be used; such aone is shown at G, Fig. 69, and at Fig. 85, and the ap-pearance of the finished core in Fig. 84. If the two endswere not alike, a half box could not be used, for the twohalf cores would then not fit together. Fig. 86 shows Pattern Making 1
. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . he core were cylindrical, a standard core could notbe used, for the two end portions which fit into the coreprint depressions must be molded and baked with thebody. In this case, a half core box may be used; such aone is shown at G, Fig. 69, and at Fig. 85, and the ap-pearance of the finished core in Fig. 84. If the two endswere not alike, a half box could not be used, for the twohalf cores would then not fit together. Fig. 86 shows Pattern Making 123 how the casting would look; note that the core print pro-jections never appear on the casting; their function isonly to forni- a support for the core in the mold. Space will not permit a further discussion of coresand core boxes, for they occur in an endless variety, andevery one would require a special description, but theforegoing should give the reader an idea of the princi-ples involved. Therefore we will proceed to explain afew small but important details such as *^fillets, ^4oosepieces, and allowance for shrinkage and machine Fig. 87—The dotted lines indicate a fillet with too great a radius inproportion to the thickness of the pattern A sharp corner should never be made on a pattern,whether it be curved or straight, but should be roundedoff; and internal corners should be filled in by a curvedportion called a ^^fillet. An exception to this rule Avouldoccur in the case of such corners as were formed uponthat side of the pattern which would rest upon the mold-ing board, as the top edge of the flange sho^vn in Such a corner could not be rounded to any ex-tent without interfering with the drawing of the sharp corner always means a weak place in the cast-ing, for strains are set up in the metal as it cools andare sometimes sufficient to cause a fracture, whereas arounded corner, or one containing a fillet, causes a moreuniform cooling stress in
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