Fig. 4
Details of Correct and Incorrect Practice in Model Making: Fig. 1, Valve Rod Joined by “Cheese-Head” Screws, Wrong, and Joined by Joint and Pin; Fig. 2, Bearing Cap Fixed with Flat-Head Machine Screws, Wrong, and with Studs and Nuts; Fig. 3, Cylinder Cover Fixed with Flat-Head Machine Screws, Wrong, and with Studs and Nuts; Fig. 4, Representation of a Brick Foundation, Incorrectly on Side, and Correctly on End
Many novices make a serious mistake in the character of the finish given to the various parts. This usually results through devoting insufficient attention to the method of manufacture adopted in engineering practice. Under the impression that a mottled appearance gives an ornamental effect, they will make a shaft end with a scraped finish. To the casual observer there would be nothing amiss, but a mistake of this kind would offend the trained eye of an engineer, because it is entirely unrepresentative. The object of scraping sliding surfaces is to obtain a greater degree of flatness by removing small inequalities. As the subsequent use of a file would only undo the work of a scraper, the surface is permitted to remain mottled, as left by the scraping tool. But the end of an engine shaft is not a sliding surface, and in engineering practice would be finished in a lathe.
Nickelplating is often resorted to in order to produce a brilliant and supposedly pleasing finish to the model of a casting. This is obviously wrong, for the actual casting—which might weigh tons—would be painted, and not electroplated.
Locomotive wheels or stacks of polished brass add to the appearance of a model only in the eyes of the uninitiated. Few persons would care to risk a railroad journey if the engine had brass wheels. Iron or steel is the correct material to use. Brass is also often used instead of iron for cylinders, connecting rods, and starting levers on models, or for steam pipes, which should be made of steel or copper.
In certain cases there may be unusual difficulties in using the correct material for a machine part made to a small scale. It is then permissible to use other material, provided some attempt is made to disguise the fact by means of an appropriate finish. Copperplating, for example, may be used to disguise some other material, if the parts should properly be made of copper. It is often convenient to make a model boiler of brass. It should not be polished but bronzed, to represent the iron or steel plates of a full-size boiler.
Take-Down Emergency Oars
When Knocked down the Oars Occupy Small Space in a Boat