The actual execution from working drawings is
comparatively an easy task; provided always that good tools are
employed, and that methods of working are adopted, in which the
perfection of the part constructed depends less on the personal
skill of the workman, than upon the certainty of the method
employed.
322. The causes of failure in this stage most frequently
derive their origin from errors in the preceding one; and it is
sufficient merely to indicate a few of their sources. They
frequently arise from having neglected to take into consideration
that metals are not perfectly rigid but elastic. A steel cylinder
of small diameter must not be regarded as an inflexible rod; but
in order to ensure its perfect action as an axis, it must be
supported at proper intervals.
Again, the strength and stiffness of the framing which
supports the mechanism must be carefully attended to. It should
always be recollected, that the addition of superfluous matter to
the immovable parts of a machine produces no additional momentum,
and therefore is not accompanied with the same evil that arises
when the moving parts are increased in weight.
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