This section is from the "Modern Machine Shop Construction, Equipment, And Management" book, by Oscar E. Perrigo. Also see Amazon: Modern Machine Shop Construction, Equipment, And Management.
For a force of ten employees there should be one foreman, four skilled pattern makers, one lathe man, one band saw and segment man, one man for keeping pattern records, finishing, varnishing, and lettering patterns, etc., and one laborer.
For a force of seven men there would be one foreman, three skilled pattern makers, one lathe, band saw, and segment man, one planer, jointer, and circular saw man, and one man for keeping pattern records, finishing, varnishing, and lettering patterns, etc. A laborer must be called from the yard or some part of the shop when wanted.
By finishing a pattern is meant putting in fillets, plugging screw-head holes, puttying, etc. In a force of ten men the lathe man will do whatever other work the foreman desires when he is not engaged on his special work. The man who keeps the pattern records looks after the issuing of patterns to the foundry and the storing of them when they are returned. An apprentice should be able to put in fillets, putty, varnish, rub down, etc., and where there are only a few men the foreman will keep the pattern records.
It should be understood that when we speak of a skilled pattern maker we mean one who thoroughly understands his business, and this is a matter not always properly understood by men who have not had practical shop experience in this particular line.
He must be able to read drawings quickly and thoroughly. He must have a good practical knowledge of molding from the patterns in the foundry, including those to be cast in "green sand," dry sand, and prepared loam; of those molded from patterns, and those "swept up" by sweeps or "strickles," and of the behavior of the various metals in casting, particularly of the different qualities of cast iron, of their liability to distortion, and the varying degrees of shrinkage.
He must have a practical idea of the effect of distortion of castings from patterns of different forms and proportions of solid and cored work.
He should know the correct amount of stock to allow for machining a casting when this is not specified on the drawings, and many other things besides the mere mechanical work of building up the pattern. In this part of the work he must know about the behavior of lumber when made into a pattern; how to so build up his pattern as to secure the greatest rigidity; to so dispose of the pieces of wood composing the pattern that its contraction and expansion shall not distort the pattern, or the wood be split from the severe strains produced by wet sand, which is always a severe trial for a pattern.
He must have his pattern divided in a proper place to mold easily and without unnecessary time to be spent by the molder; how to so divide his pattern as to render molding easy; when to make the pattern solid to avoid unnecessary expense, and when the job can be swept up in sand or loam and so practically to avoid the expense of a pattern.
All these and many minor points relating to his work he must get by study and experience in order that he may be classed as a skilled pattern maker, and to accomplish this he must be a man of considerable ability to begin with, consequently we must not expect him to be a cheap man.
A great deal of care should be exercised in selecting lumber for use in making patterns, and it will usually be found difficult to obtain really first-class stock of this character. Properly dried and seasoned lumber is not easily found, and even if it is said to have been kiln-dried it may have been left exposed to damp atmosphere afterwards and so absorbed sufficient moisture to make it necessary to keep it stored for quite a time in order to have it fit for use.
It is almost impossible to know just the condition of lumber when it is purchased, either in the rough or planed. It is therefore one of the great conveniences, if not a real necessity, to have a dry-room, heated with a steam coil, so that lumber may be thoroughly "dried out" before being taken into the pattern shop for use.
Care should be taken that this dry-room is not kept at too high a temperature, as such a condition will result in "season checks" in the surface and the ends of the lumber, owing to the too rapid contraction of the surface before the center of the plank, or board, is thoroughly dried. And even after it has been through the dry-room it should not be piled up horizontally, with the flat sides together, but kept on edge, in racks suspended from the overhead timbers of the pattern shop, and in which the lumber is held in position by vertical strips.
Previous to being placed in these racks the lumber should be planed to certain regular thickness from a quarter of an inch to one inch by sixteenths, and from one inch to two inches by eighths. Lumber thicker than two inches should ordinarily be left in the rough until wanted for use, unless there are many large and heavy patterns to be made. This lumber may be piled horizontally with strips laid between the planks every six feet or less, and directly over each other.
As to the kind of lumber to be used, white pine is the most common, although much cherry is used for small patterns and should be used for the smaller loose pieces of pine patterns. In the Western States the author has seen butternut used to good advantage for patterns, particularly where the pattern has much hand work, with the gouge to be done. It cuts easily and smoothly and is stronger than white pine. Mahogany makes a very nice small pattern, but is unnecessarily expensive for any other patterns.