rd 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.

Commencing with a countersunk head as the strongest form of head, the
greater the fillet permissible under the head of a rivet, or bolt, the
greater the strength and the decrease in liability to fracture, as a
fillet is the life of the rivet.

If rivets are made of iron, the material should be strong, tough, and
ductile, of a tensile strength not exceeding 54,000 pounds per square
inch, and giving an elongation in _eight inches_ of not less than
twenty-five per cent. The rivet iron should be as ductile as the best
boiler plate when cold. Iron rivets should be annealed and the iron in
the bar should be sufficiently ductile to be bent cold to a right
angle without fracture. When heated it should be capable of being
flattened out to one-third its diameter without crack or flaw.

[Illustration: FIG. 15. Solid Die Rivet.]

[Illustration: FIG. 16. Open Die Rivet.]

If rivets are made of steel they must be low in carbon, otherwise they
will harden by chilling when the hot rivets are placed in the cold
plates. Therefore, the steel must be particularly a low grade or mild
steel. The material should show a tensile strength not greater than
54,000 pounds per square inch and an elongation in _eight inches_ of
thirty per cent. The United States government requirements are that
steel rivets shall flatten out cold under the hammer to the thickness
of one-half their diameter without showing cracks or flaws; shall
flatten out hot to one-third their diameter, and be ca