F. W. PUTNAM

This series of articles on pattern making will be so written as to be of value to those amateurs whose stock of tools is not large, and to those whose practical experience with model making is very limited. It is surprising to see the amount of ingenuity displayed by some model makers in attempting to supply a lack of pattern making ability. If the same amount of time and patience had been properly directed, the model maker would have been able to make patterns, not for one model alone, but for about anything else he wished to make.

It is not pleasant, after much time and labor have been expended upon the wooden model, to hear the decision of the founder that it is quite impossible to mould and cast it in metal. Yet nothing is more common, and the cherished pattern has frequently to be cast aside and replaced by one of totally different construction. A pattern maker, in addition to skill in the use of tools, must be able to make drawings and sketches as well as read them, as it frequently happens that the pattern must have a shape differing from that shown in the drawing. He must therefore be able to make the modified drawings necessary for his work, and so must thoroughly understand the methods of the foundry. With these thoughts in mind the present series of articles are written.

These articles, then, are to take up also the principles of moulding and casting, and the series will be long enough to give instruction to such an extent that the model maker will be able to embody his ideas for castings in patterns, to adapt means to ends, and to avoid making the final results subservient to means. I hope to be able to explain foundry practice in such a way as to prevent the reader from making any mistakes in his designing, which might lead to expensive castings because of their being impractically designed and thus costly to make through defective knowledge of moulding.

Having finished our introduction, let us first examine very briefly something of the history of pattern making. The art of moulding has come down to us from a very remote period we find evidences of its practice by the most ancient nations in articles found among the ruins of temples, palaces, fortresses and cities. Those learned men, who have read our old earth's unwritten history, 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.

Lack of space forbids any lengthly review of the history of pattern making, and I will only say that, whatever the source of the technology of the art, we in our own day can show nothing superior, either in design or execution, over the work of men whose names and methods are lost. The more modern idea of the division of labor has made pattern making a distinct art. A generation ago a machinist was required to be able to work upon both wood and metal; he constructed his frames of wood and made the patterns for his cast metal work; he was today a woodworker, tomorrow a lathe hand and the following day a vise band.

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 moulding 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 select 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. Experience is a great teacher, and the amateur 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

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castings were satisfactory, noting the defects in the latter, if any, together with suggestions for the remedy for those defects. A pen and ink sketch of the patterns made in the margin of the record will add to its usefulness, besides accustoming the hand to make correct sketches and a clear explanation of the work done. 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 moulding well.

Before we commence the actual making of patterns it will be well to give some instructions as to wood and other materials to be used in this work and also to anticipate some of the difficulties that may be met in the use of tools, etc. In selecting stock for patterns the following must be considered : - First, its tendency to warp ; second, its tendency to bend, and third, its tendency to shrink. Newly felled timber contains sometimes as much as 50 per cent of its weight of water. If it lies for some time in a dry and airy place it will lose nearly half its amount of water by evaporation. During the process of drying, timber decreases in volume or shrinks. If exposed again to moisture it increases in volume or swells. Timber is often used under condition which do not permit it to shrink or swell freely in all directions; consequently it shrinks or swells more in one place than in another. When one part of a piece of timber shrinks more rapidly than an adjacent part, the wood cracks. If, on the other hand, one part swells more than another, or if the adjacent part meets with some obstacle to its expansion, the timber changes in shape, it becomes warped.

In many kinds of trees, when the trunk is sawn across, a considerable difference may be observed between the appearance of the inner and older and the outer and younger concentric annual layers. The inner layers making up the heart of the tree are generally firmer and closer in texture and darker in color than the outer or sap wood; these outer layers being less compact, lighter in color, and full of sap. The parts nearest the sap wood shrinks more rapidly than the heart wood and cracks or checks are the result.

Fig. 1 is a sectional view of a log showing very clearly the annular rings and the checks as just referred to. Fig. 2 is a sectional view of a log with the round edges removed, the dotted lines indicating the cuts taken in sawing the log into parallel longitudinal cuts. Fig. 3 shows how the planks will shrink as the moisture dies out. The broadest portion shown shrinks least in breadth, most in thickness; least nearest the centre, most near the sides. The outside planks, however, shrink most in breadth, in the direction of the annual layers, and least in thickness. The planks lying between shrink differently on different sides, and become convex nearest the centre and concave toward the outside because of the corners being drawn up.

It will be seen then that planks containing the most heart wood warp the least, and so, in order to reduce the tendency to warp, the boards or planks are sometimes sawed at right angles to the annular rings, making four pieces. Each piece is then laid back down and sawed into boards. This method, called quarter-sawing, is wasteful in lumber but reduces warping to a minimum, and in certain kinds of wood, as oak and sycamore, produces very beautiful results on account of the manner in which it intersects the medullary rays.

For our work, pine will be the most servicable of the different kinds of woods used by the pattern maker. Good stock, straight grained and free from knots should be procured, as the difference in cost between good and inferior wood in the small pieces required for each pattern is as nothing in comparison to the value of the work put into it, and a pattern may easily become valueless through the wood being checked or not thoroughly seasoned.

Pine, if carefully selected, is easily worked and possesses, at the same time, strength enough for all but the most delicate kinds of patterns. The chief objection to pine for small patterns is that it is soft and soon gets dented from repeated moulding, but this objection we need not consider, as the reader is not likely to need more than three or four castings from the same pattern. Also, by carefully shellacing the pine patterns, we shall be able to make the surface very nearly as hard and glossy as hardwood ones, and so secure the same smooth castings.

When pine is straight grained, the marks left by the saw on a plank will show an even roughness throughout its length, the softer the plank the rougher the appearance of the edges. If the surfaces sawed seem to be smooth, the stock will generally be found to be hard and difficult to work. When the surfaces sawed are rough in spots and smooth in others, the grain is croodek and it will be found that in planing, the grain tears up and a smooth surface is impossible.

When a great many castings for fine work are required from a pattern, a pattern is made for an iron casting to be finished as a pattern. These iron patterns are very durable, leave the sand easily and will not warp. They are, however, expensive to make, and so mahogany is very extensively employed for fine or durable pattern work. Mahogany warps but little and does not decay, so it is really the most desirable of all woods used in pattern making, where the first cost need not be considered.

Bay wood, an inferior and much cheaper kind of mahogany is much used, especially in England. If you buy bay wood, choose it light colored and get it as straight grained as possible, and without any fancy markings. Avoid a board that is "fuzzy" or "wooly" on the surface as it does not work well, this being opposite to the grain of pine stock, which when rough from the saw is generally soft and easily worked.

Next to mahogany we may rank cherry. It is a very durable wood, but is much more liable to warp or twist than mahogany and is rather hard to work. Small patterns and core boxes are sometimes made from hard maple, while for very fragile patterns sycamore is sometimes used, as it is so white and close grained that you can draw neatly upon it, and see your lines distinctly when paring or carving, a most important point in accurate work. In buying small pieces of wood, I may say that most lumber dealers are willing to cut off a piece of board at a little extra cost per square foot. Do not buy, however, from a builder or cabinet maker if you can avoid it, as they will generally charge a much higher price.