sions have been clearly traceable to the abuse of this
tool. Then, next, specifications insisted that all holes should be
enlarged by reamering _after_ the plates were in place. But even that
did not prove a safeguard, because it often happened that the metal
reamered was nearly all removed from one side of a hole, so leaving
the other side just as the punch had torn it. Ultimately came the era
of drilling rivet-holes, to which there is no exception now in
high-class boiler work. For average girder and bridge work the
practice of punching and reamering is still in use, because the
conditions of service are not so severe as are those in steam boilers.

Flanging signifies the turning or bending over of the edges of a
plate to afford a means of union to other plates. Examples occur in
the back end-plates of Lancashire and Cornish boilers, the front and
back plates of marine boilers, the fire-boxes of locomotive boilers,
the crowns of vertical boilers, the ends of conical cross-tubes, and
the Adamson seams of furnace flues. This practice has superseded the
older system of effecting union by means of rings forming two sides of
a rectangular section (angle iron rings). These were a fruitful source
of grooving and explosions in steam boilers, because their sharp
angular form lacked elasticity; hence the reason for the substitution
of a flange turned with a large radius, which afforded the elasticity
necessary to counteract the effects of changes in temperature. In
girder work where such conditions do not exist, the method of union
with angles is of course retained. In the early days of flanging the
process was performed in detail by a skilled workman (the angle
ironsmith), and it is still so done in small establishments. A length
of edge of about 10 in. or a foot is heated, and bent by hammering
around the edge of a block of iron of suitable shape. Then another
"heat" is taken and flanged, and another, until the work is complete.
But in modern boiler shops little hand work is ever done; instead,
plates 4 ft., 6 ft., or 8 ft. in diameter, and fire-box plates for
locomotive boilers, have their entire flanges bent at a single squeeze
between massive dies in a hydraulic press. In the case of the ends of
marine boilers which are too large for such treatment, a special form
of press bends the edges over in successive heats. The flanges of
Adamson seams are rolled o