If we attempt to define the sub-press die, we find that we cannot, define it as a special class of die, but merely as a principle on which all different classes of dies, cutting as well as shaping dies, may be constructed and worked. The sub-press principle is simply that the upper and lower portions of the die, the punch and die, are combined into one unit either by guide rods fastened into the lower part of the die, and extending through holes in the upper part, or by some other provision for guiding. This construction permits of a high degree of accuracy, eliminates the necessity of lining up the punch and die each time they are set upon the press, and thus saves a great deal of time and cost.

Owing to the large number of parts of which a sub-press die is composed its first cost is, of necessity, much higher than that of an ordinary die. When, however, we consider that a sub-die, when properly made, will run ten hours per day, for weeks at a time, without grinding, the first cost sinks to a minimum. In using an ordinary double die it is almost impossible to obtain two blanks that are exactly alike, one reason being that the stock to be punched is more or less wrinkled and does not lie flat on the face of the die. The consequence is, therefore, that after the piercing punches have perforated the wrinkled stock, and it is then flattened out, there is a greater distance between the holes than there is between the punches. Also, the pilot pins that are depended upon to locate the stock cannot do so exactly, since they are made a trifle smaller than the piercing punches in order to prevent them from pulling the blank up out of the die. On a certain class of work the double die answers all purposes, but when accuracy is required a sub-die is the only one that will give satisfaction.

In order to avoid a complicated drawing and to set forth the principles of the die in such a way that they may be readily understood by those not familiar with sub-dies, the die used for punching an ordinary washer has been selected for an illustration. The general principles of sub-dies are, of course, the same whether one or one hundred punches are employed. Having selected a frame with its proper cap, as shown in Fig. 1, of size suitable to the work, it is placed in a chuck, being held by the upper end, and, having faced off the bottom, the recess A A is bored to fit snugly the corresponding step on the base of the press. This base is finished on both top and bottom, and has a step, above referred to, turned to fit the bottom of the frame. A slot at G is cut in each end to receive the finger straps by means of which the frame is fastened to the face-plate of a lathe.

The center is recessed to receive the stripper plate and blanking punch, and a hole is drilled completely through to allow scrap punchings to fall to the floor. The base and frame are then fastened together by means of bolts and dowel pins as shown. Together they are clamped to the face-plate of the lathe, being centrally located by means of a plug center which fits the taper of the lathe spindle, and passes through the hole in the center of the base. In this position the frame is bored out to a taper of about one-half inch per foot. After boring, a splining tool is substituted for the boring tool, and with the lathe locked by means of the back gears, three or four grooves B are cut the entire length of the bore by sliding the carriage back and forth. At the same setting the upper end of the frame is faced off and threaded to receive the cap which is screwed on the frame. After the cap is in place, the hole for the plunger in this cap is bored out to the required size. This insures the hole in the cap being central with the inside of the frame.


CONSTRUCTION AND USE OF SUB-PRESS DIES

The sub-press die is an old device dating back at least one, and possibly two generations, and having its origin in watch and clock factories where its ability to perform blanking operations of the most delicate nature was early recognized and fully appreciated. That this tool, though familiar in the field just mentioned, has yet capabilities in other directions which have not hitherto been fully recognized, is the impression that must be strongly borne upon an appreciative mechanic who is acquainted with the work being done in the shops of the Sloan & Chace Manufacturing Co., of Newark, N. J. This firm has for many years built precision machinery for watch makers, fine tool makers and others, whose work requires great accuracy. The tools described in the following were constructed by this firm.


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