Tables of Diameters, Circumferences and Areas of Circles, and the Contents in Gallons, at a foot in depth, Fractions of an Inch into Decimals of a Foot, 301 Inches and Fractions into Decimals of a Foot, 301 Inches into Decimals of a Yard, To find the Chordial Pitch of Teeth, Table of the Radii, Number of Teeth, and Pitch of Gear Wheels, from 1 to 1 inch Pitch, THE PATTERN MAKER'S ASSISTANT. CHAPTER I. PATTERN MAKING. THOSE savans who have read our old earth's unwritten history in and from its strata, tell us that, in ages far remote, men made tools and contrivances of bronze, which, being an alloy, necessitated the fusion and casting of the metal. This casting involves the use of patterns, and pattern making may therefore lay claim to the highest antiquity. But the modern idea of the division of labor has exalted it to be a distinctive art; in the last generation, for instance, a good machinist (or rather engineer or millwright, for those terms were then applied to builders of machinery,) was required to be alike expert in working upon both wood and metal. He constructed his framing of wood, and made the patterns for his cast metal work; he was to-day a lathe hand, to-morrow a vise hand. As, however, the present age of iron dawned, it became apparent that working in wood and in metal must be separated, not only because the handiwork could be more cheaply produced by reason of the increased skill arising from continuous practice, but also because the amount of knowledge required to make an artisan skillful in either the manufacture of wood or of iron, was too great to be thoroughly mastered in the working lifetime of an ordinary, or even an unusually expert workman. Hence modern intelligence soon discovered that better as well as cheaper work could be obtained by a practical education in one particular branch of usefulness, and hence pattern making has taken its place as a specialty. The field of usefulness of cast iron has developed to a remarkable extent during the last twenty years, and the same remark applies to cast steel during the last ten years; both of these materials are steadily encroaching upon the domain of usefulness of wrought iron, stone, and bricks and mortar. So that the field of application for pattern making is stretching outward and onward, to the discomfiture of its rivals. From these considerations, we may readily perceive that a real proficiency in pattern making will exercise to the utmost the skill of the workman, on account of the unceasing variety of the patterns, in form and in the purposes for which they are designed; and the advantage of a retentive memory is evident when we consider that years may elapse ere the same pattern maker may be called upon to exercise his skill upon the same or a similar piece of work. In this art, there are to be considered many details that are seldom or never shown in drawings; such, for instance, as the amount necessary to allow on the pattern for finishing certain parts of a casting, and on what part such allowance is required; and the method which has been proved by experience to be the safest and most expeditious in molding from a certain kind of pattern. But above all these considerations lies the fact that drawings merely show the shape which the finished pattern is required to have, leaving it entirely to the judgment of the pattern maker to elect in what way the various pieces of wood (of which the pattern is constructed) shall have the grain lie, and how they shall be fastened or held together. There is, it is true, an unwritten practice which has obtained universal observance in particular branches of pattern making; but in the newer fields into which the art has advanced and is ad vancing, this unwritten practice is merely in the process of formation, which state of things must continue so long as casting is discovered to have new arenas of application. A goodly store of well remembered experience is therefore invaluable to the pattern maker; and this being so, the quicker it is obtained the better. Hence the learner should always keep a record of the work which falls under his observation, in which record the sizes and proportions of the work, the method of putting it together, the time taken in its production, and (if possible) whether the castings were satisfactory, noting the defects in the latter, if any, together with suggestions for the remedy of those defects. A pen and ink sketch of the pattern made in the margin will add to the usefulness of the record, besides accustoming the hand to making correct sketches and elucidating the explanation. The operative's intelligence will be much exercised in the shaping and building-up of patterns, depending as this does on the strength of the material of which the casting is to be made, the strength of the pattern itself, and the desirability of its molding well. Dr. Andrews has well said (in the English Mechanic): "The correct forms to be given to the materials employed in the construction of tools or machinery depend entirely upon natural principles. Natural form consists in giving to each part the exact proportion that will enable it to fulfill its assigned duty with the smallest expenditure of material, and in placing each portion of the materials under the most favorable conditions of position that the circumstances will admit of. Such natural form is not only the most economical, but, strange to say, it is always correct in every respect, and is invariably beautiful and lovely in its outlines." I may now mention the qualifications necessary to enable an artisan to become a good pattern maker: First: As the idea of the size and contour of the article or work required will be conveyed to him by drawings, it is neces |