Excerpt from Modern Punch and Die Construction

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 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 pro perly 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 con sequence 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.

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