SPRING AND ADJUSTING SCREW FOR DRAWING INSTRUMENTS.
[Illustration: Fig. 15]
It will be seen that we can apply a spring _D_ and adjusting screw
opposite to the leg which carries the pen or pencil point of all our
dividers if we choose to do so; but it is for metal drawing that such
points are of the greatest advantage, as we can secure an accuracy very
gratifying to a workman who believes in precision. For drawing circles
on metal, "bar compasses" are much the best, as they are almost entirely
free from spring, which attends the jointed compass. To make (because
they cannot be bought) such an instrument, take a piece of flat steel,
one-eighth by three-eighths of an inch and seven inches long, and after
turning and smoothing it carefully, make a slide half an inch wide, as
shown at Fig. 15, with a set-screw _h_ on top to secure it at any point
on the bar _E_. In the lower part of the slide _F_ is placed a steel
tube like _C_, shown in Figs. 12 and 14, with set-screw for holding
points like _B B'_, Fig.
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