5/8 or 0.625 | 3/16 or 0.1875 | 15,420 | 13,750 | 5/8 or 0.625 | 1/8 or 0.125 | 10,670 | 9,320 | 5/8 or 0.625 | 1/8 or 0.125 | 11,730 | 9,580 | ------------------------------------------------------------
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It will be seen from the above that the punched bars had the greatest strength, indicating that punching had the effect of strengthening instead of weakening the metal.  These experiments have given results just the reverse of similar experiments made on boiler plates; but the material, such as above experimented upon, is what should be placed in boilers, tough and ductile, and the manner of, and care taken in, punching contribute to these results.

It is usual to have the rivet holes one-sixteenth of an inch in diameter larger than the rivets, in order to allow for their expansion when hot; it is evident, however, that the difference between the diameters of the rivet hole and of the rivet should vary with the size of the rivet.

The hole in the die is made larger than the punch; for ordinary work the proportion of their respective diameters varies from 1:1.5 to 1:2.

As I have before stated, the best plate joint is that in which the strength of the plate and the resistance of the rivet to shearing are equal to each other.

In boilers as commercially made and sold the difference in quality of the plates and rivets, together with the great uncertainty as to the exact effect of punching the plates, have, so far, prevented anything like the determination either by calculation or experiment of what might be accepted as the best proportions of riveted joints.

In regard to steel plates for boilers Mr. F.W.  Webb, of Crewe, England, chief engineer of the London and Northwestern Railway, has made over 10,000 tests of steel plates, but had only two plates fail in actual work; these failures he thought were attributable solely to the want of care on the part of the men who worked the plates up.

All their rivet holes for boilers were punched in a Jacquard machine, the plates then annealed, and afterward bent in rolls; they only used the reamer slightly when they had three thicknesses of plate to deal with, as in butt joints with inside and outside covering strips.  These works turn out two locomotive boilers every three days.

The Baldwin Locomotive Works, which turn out on an average three locomotives per day, punch all their rivet holes one sixteenth inch less in diameter and ream them to driven rivet size when in place.  They also use rivets with a fillet formed under head made in solid dies.

Rivets.—­Rivets of steel or iron should be made in solid dies.  Rivets made in open dies are liable to have a fin on the shank, which prevents a close fit into the holes of the plates.  The use of solid dies in forming the rivet insures a round shank, and an accurate fit in a round hole.  In addition, there is secured by the use of solid dies, a strong, clean fillet under the head, the point where strength is most needed.