The softened disc is then
taken to the rolls (Fig. 45). The rolls are loosened until the disc can
be pressed between them. Looking through the interval between them the
rolls should appear exactly parallel; if they are not, one adjusting
screw should be loosened and the other tightened until parallelism is
obtained. The rolls are now turned and the disc should be drawn through
without any great effort. Beginners are apt to err by trying to do too
much with one turn of the handle. It is easy to stop whilst the rolls
are only just gripping the metal and then to bring the disc back by
reversing the action. If the disc was originally level and the rolls
are parallel, the metal will appear as a strip which has been merely
lengthened. If the rolls are tighter on one side the strip will be
bowed; the tighter side will correspond with the outer curve of the
crescent. A mistake of this kind may be amended by passing the strip
through the rolls the other way, so as to reverse the irregularity and
so straighten the strip. The screw on the looser side should then be
tightened until parallelism is obtained; after which more care should be
taken to tighten the two screws equally. The rolling should be stopped
when the strip is 3 or 4 inches long and of the thickness of an ordinary
visiting card. The strip should be annealed during the rolling and again
at the finish.
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