OF
A DIFFERENTIAL PUNCH MACHINE
For Engravers.
I was the rather induced to attend a second time to the differential Steel-yard, because I had it in contemplation to apply that principle to the present purpose; since, to make flat punches, is to some engravers a more desirable thing than to make cylindrical ones. I am not fully persuaded that it is even possible to transfer a large pattern, from a flat die to a flat punch, by any pressure acting simultaneously on the whole surface. In those cases, if there is much work, the whole surface goes down; and the parts that form the pattern do not rise. But, all that can be done in this case, is, I believe, feasible by the Machine now to be described.
[Plate 23], gives in [fig. 3 and 4], a representation of this Machine; A B and C D, are two slides, having wedge-formed ends above A and below D, well made, well steeled, and well tempered. One of these slides contains the die and the other the steel prepared for the punch (see B C). These wedge-ended slides are embraced by two levers E F, G H, which are themselves connected by two stirrups I K and L M, better shewn at [fig. 3]. These latter are supposed in [fig. 4] to be broken at L M, to leave the levers E F and G H more visible. They are formed, at the turning below, into wedge-like edges a b; well hardened, that clip the nicks c d of the lower lever: and at the top of the Machine their arms e f, pass through the caps m n, above which they are nutted like a common bolt, and made to press strongly on the main lever E F. The stirrup placed to the right hand, presses in particular, by it’s cap n, on the moveable step o, exactly in the notch q: this step having a backward and forward motion communicated by the regulating screw p. Before beginning to use this Machine, I make all it’s arms A E, A g, D e, D d, equal, when it’s power (see [page 162]) is infinite; and to put it in a working state, I turn the screw p backward, say one half round: which motion (if the screw has 20 threads to the inch) makes a difference in the two arms A r and A q of 1⁄40 of an inch, and the virtual centre of the Machine is therefore 1⁄80 of an inch from the former point A, that is from the edge of the slide A in this [fig. 3]. Supposing now, the whole working lever E F to be 3 feet, and the workman’s force to be 100lbs. in each arm, then by displacing the lever to any proper distance from F towards f, he will produce a pressure between the die and the punch of 200lbs. multiplied by 1440, the number of times that 1⁄80 of an inch is contained in 18 inches.—That is, a pressure of two hundred and eighty-eight thousand pounds!
I have been seduced, by the anticipated brilliancy of this result, from the regular course of description,—and the plate w x, y z, which forms the base or frame of this whole Machine has not yet been spoken of. But that plate is supposed screwed down to a horizontal bench, at or near the height of a man’s breast; the slides or cases are fastened to it, and the man is supposed to work the Machine nearly as he would a die-stock in tapping a screw. This however is not indispensable; the Machine might be placed vertically, and these motions given by any proper mover; or a weight may be suspended to the arm F, so as to add continuity to pressure. It is however important, that the position should comport with the frequent extraction of the punch in order to examine the progress of the work, or cut away any redundant metal. I have before given it as my opinion that much could not be expected from mere pressure: but this is a pressure of a peculiar kind, consisting of immense powers with very short motions. In this respect it is just what was wanted, as it can be renewed and repeated frequently, without loss of time. And the more to facilitate this delicate operation, the hollow slides or cases B C, are made slightly pyramidical, to be furnished with set-screws on the four sides, by which to change the place of bearing; and thus to meet the case of a flat punch with the advantage of impressing it by portions, so as to have only to finish it by brute pressure.
The foregoing application of the principle of the differential Steel-yard, is, I think, important, and founded on unobjectionable principles; for although by changing alone the place of the step o, we disturb a little the parallelism of the stirrups I K, and L M; we do it not enough to produce, any material change in the theoretical result. With respect then to the lesser properties of this Machine, I leave them with confidence in the hands of those whom they most concern—who doubtless, will treat them with greater practical utility than I could myself hope to do.