Page:Popular Science Monthly Volume 92.djvu/470

 454

��Popular Science Monthly

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��The die face, in this particular case, is treated differently, as it is considerably higher near the center than at the outside. This gives a shearing cut on the stock, doing the work with far less power than if the die face were perfectly flat. The die must also have clearance as shown by the dotted lines. The hole is straight for a short distance ■ — about 1/32 in. — then it becomes larger on a con- stant taper, the amount of taper being the same as for the punch. This pro- vides a clearance for the punchings and permits them to fall through easily. The shallow hole in the side of the die is for the re- taining set screw shown more clearly in Fig. 1,

The die and punch shown in Fig. 9 is for making a five pointed star in saucer shape. As this product is in the punching it must be formed in one operation. To do this the die face is made flat an^ the punch to shear, as shown. The amount of

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���Details of the stripper base and plate; also jaw clips to hold the parts

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��CURLING PUNCH ft DIE. FIG. 10.

��Three kinds of dies and punches showing their construction; also sample of work

shear given to the punch face governs the amount of bend in the i)ro(luf'1, and, in special cases, it must be found by trial. With this punch it will be seen that the

��points of the star are pierced first and are forced through as the punch enters the die, the punch continuing to shear the stock and to bend it into the desired shape.

The concave to the punch face is produced by grinding. In the case of very small punches, the concave may be given by drilling before the punch is hardened, then, after the hardening, lapped with a piece of wood, oil an.d emery. The flutes may be chipped and filed, if there is no means of mill- ing them with a formed cutter.

The die is marked out and drilled with a small drill so that it does not quite touch the outline or cut into the next drilled hole. To prevent the holes breaking into one another, fill the last drilled hole with a metal plug. Another metal part in which the punch- ing is the product is shown in Fig. 10. It is a complete ring. As in the other case, the die face is left flat and the shear to the punch face is all to one side as shown. The angle of shear determines the diameter of the finished ring. This also must be de- termined by trial.

If the face of the punch is made straight on an angle it will require considerable grinding throughout the cutting and will have a very short life. To obviate this wear, a short portion at the heel should be made equal to about one-half the thickness of the stock to be punched. At the terminal of the ring there will ap- pear a straight, flat part, equal to the amount of the flat part on the punch. This can be finished by grinding or ham- mering.

These holding devices are not expensive to make, and" where there is a good-sized vise at hand, small, round and square punches and dies may be used to advan- tage in punching holes in sheet metal for ordinary riveting or for tapped holes in fastening parts together with machine screws. The punches and dies for these operations are easily made. — J. B. Murphy.

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