STRENGTH OF PUNCHED AND DRILLED IRON BARS.

HOOPES & TOWNSEND.

----------------+------------------+----------------+----------------+
Thickness of bar|Thickness outside | Punched bars | Drilled bars |
in inches. |of hole in inches.|broke in pounds.|broke in pounds.|
----------------+------------------+----------------+----------------+
3/8 or 0.375 | 3/8 or 0.375 | 31,740 | 28,000 |
3/8 or 0.375 | 3/8 or 0.375 | 31,380 | 26,950 |
5/8 or 0.625 | 1/4 or 0.25 | 18,820 | 18,000 |
5/8 or 0.625 | 1/4 or 0.25 | 18,750 | 17,590 |
5/8 or 0.625 | 3/16 or 0.1875 | 14,590 | 13,230 |
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