A similar result seems to take place in any change of mental
exertion; the attention bestowed on the new subject not being so
perfect at first as it becomes after some exercise.
221. 4. Change of tools. The employment of different tools in
the successive processes is another cause of the loss of time in
changing from one operation to another. If these tools are
simple, and the change is not frequent, the loss of time is not
considerable; but in many processes of the arts the tools are of
great delicacy, requiring accurate adjustment every time they are
used; and in many cases the time employed in adjusting bears a
large proportion to that employed in using the tool. The
sliding-rest, the dividing and the drilling-engine, are of this
kind; and hence, in manufactories of sufficient extent, it is
found to be good economy to keep one machine constantly employed
in one kind of work: one lathe, for example, having a screw
motion to its sliding-rest along the whole length of its bed, is
kept constantly making cylinders; another, having a motion for
equalizing the velocity of the work at the point at which it
passes the tool, is kept for facing surfaces; whilst a third is
constantly employed in cutting wheels.
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