Models made as a pastime or for exhibition purposes should represent correctly the full-sized machine, not only as regards general design but also in the proportioning of parts, the finish, and the choice of materials. The satisfaction derived from the possession of a model is greater when it is truly representative. Study and careful measurement of the original are necessary to attain this result, and provide valuable experience in the application of correct mechanical principles.
The most conspicuous, though perhaps not the most frequent, errors made by amateurs are in the proportioning of the various parts. This usually arises from insufficient study of the original machine, and is often sufficiently glaring to attract the attention even of a casual observer. The foundation or base of a model stationary engine, for example, is often painted to resemble brickwork. This is correct, provided the spaces are proportioned so as to represent bricks and not three-ton slabs of granite.
Mistakes are made in the selection of pulley wheels, both as regards the character and the size of the pulley that would be suitable for the particular purpose.
The “cheese-head” or flat-head machine screw appears to have a peculiar fascination for the model maker, judging from the frequency with which it is misplaced. It is only necessary to consider what would happen in a full-sized machine if such screws were used for making joints in valve rods, cylinder covers, slide bars, for fixing bearing caps, and the like, to realize how completely such a defect mars the appearance of a model to a discriminating eye. Bolts, or, in some cases, studs and nuts, should be used to give an appearance of correct workmanship.
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