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.
Similar parts of machines of the same type take the same numbers. Thus, if the letter of a machine is B, the patterns will be marked B1, B2, B3 and so on. When a change is made in a pattern, a letter X is added, making the pattern B3 read B3X. If changed a second time it will become B3XX. Further changes would be indicated by one X followed by a number to indicate the number of changes that had been made. For instance, if it had been changed the fourth time it would be marked B3×4. If the swing of a lathe is to be increased or a planer to be widened, by a special order, the new patterns made necessary by this change would be marked with both of the letters indicating the machines, as for instance, the letter K, indicating a 30-inch planer to be widened to 36 inches, the letter being L, the new patterns necessary would be marked K-L, the hyphen being used to indicate that two machines are meant.
Where a machine designation necessitates two letters of the alphabet in consequence of the fact that the letters are exhausted by the variety of machines built, the hyphen is omitted. The letters I O X are omitted as designating letters, as the first two so nearly resemble figures, and the letter X is used to indicate alterations of the patterns.
Pattern letters and figures should be formed with two sharp points on the back, which may be forced into the wood of the pattern and thus hold them securely. The addition of a little thick shellac varnish will hold them more firmly.
These letters and figures may be purchased, or they may be cast in the pattern shop, and as a large number of them are used this will be the more economical way to obtain them. A brass mold in two parts, hinged together, may be made, one part having the letters formed in it, and the other with tapering holes for forming the points on the back of the letters. The metal used is lead, to which is added a small quantity of antimony. A still better alloy is composed of lead 70 parts, antimony and bismuth each 15 parts. The mold is heated over a gas flame, while the metal is melted over a Bunsen burner. Care should be taken not to overheat either of these alloys. They should be just hot enough to burn a pine stick to a rich brown.
These letters and figures should be of the style known as sharp faced gothic, size three-eighths, or half inch, and are used only for indicating the letter of the machine, the number of pattern and the changes that have been made in it. The letters for the name of the firm, or company, which appear in prominent places on the machine, should be also of the sharp faced gothic style and of a size suitable for the available space. They should be purchased and kept in stock in proper boxes or cases.
Usually three or four sizes of pattern letters and figures will be sufficient. These pattern letters, having flat, smooth backs are often fastened to the pattern with small wire brads, which hold them very securely, but are likely to show roughly on the casting unless the job is very carefully done.
A much neater and quicker job may be done by first putting a coat of light shellac on the backs of the letters, then a rather thick coat on the pattern and placing the letters on this before it is dry. In either case a line should be drawn on the pattern for the tops of the letters, and they should all be laid on and the position of each marked before fastening them to the pattern.
The reason for using the sharp gothic style of letters in preference to roman or fancy styles is that there is such a large amount of draft to the sides of the letters that they draw very easily from the sand, and also, that for nearly all classes of castings the plainest letters have a much better appearance than the more ornamental or complicated ones.
Pattern letters and figures should be kept in convenient cases or boxes so as to be securely protected and readily found when wanted. The most convenient form of case is that shown in Fig. 206. This case is 20 inches wide and 28 inches long. The strips around the ends and back are five-eighths inch thick and one and a quarter inches wide; the front is the same thickness and one and three quarter inches wide; the bottom being half an inch thick. The partitions are a quarter of an inch thick, and are "notched together" as in a type case. The letter boxes are 3 × 4¬ inch, except for the letter X, which is 4¬ × 6¬ inch, as many of these are used in marking changes of pattern. The figure boxes are 2 x 3 inch, except that of the figure 6, which also answers for the 9, the box being 3 x 4$ inch. Each case is furnished with two drawer pulls, and the front should be plainly marked with the size of the letters and figures contained in it.
The care of wood fillets, so as not to injure the feather edges, is important, and a safe receptacle should be provided for them. In order to have these articles, as well as leather fillets, brass dowels, wood dowels, rapping plates, etc., properly cared for and arranged in an orderly manner where they can be readily found, the case or cabinet shown in Figs. 207 and 208 is designed to meet these requirements. The lower part of this case is 59 inches wide, 20$ inches deep and 26 inches high, and contains six of the cases for pattern letters and figures, as shown in Fig. 206, twelve bins for malleable iron rapping plates, and three drawers properly divided for holding brass dowels. The upper part of the case is 8« inches deep and contains at the top six spaces for wood dowels, and beneath these six spaces for wood and leather fillets, both kinds being placed in the same space. The wood fillets being made in four-foot lengths there is ample space for them. This case should be made of ⅞-inch pine, with a back «-inch thick. It will be found a great convenience, as well as a means of saving these articles from waste and injury.
Fig. 206. Case or Drawer for Pattern Letters and Figures.
Cabinet for Pattern Letters, Fillets, Dowels, Rapping Plates, etc.