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. 13. At the opposite end of the bar _E_ is
placed a looped spring _G_, which carries a steel tube and point like
the spring _D_, Fig. 14. Above this tube and point, shown at _j_, Fig.
15, is placed an adjustment screw _k_ for fine adjustment. The inner end
of the screw _k_ rests against the end of the bar _E_. The tendency of
the spring _G_ is to close upon the end of _E_; consequently if we make
use of the screw _k_ to force away the lower end of _G_, we can set the
fine point in _j_ to the greatest exactness.

The spring _G_ is made of a piece of steel one-eighth of an inch
square, and secured to the bar _E_ with a screw and steady pins at _m_.
A pen and pencil point attachment can be added to the spring _G_; but in
case this is done it would be better to make another spring like _G_
without the point _j_, and with the adjusting screw placed at _l_. In
fitting pen and pencil points to a spring like _G_ it would probably be
economical to make them outright; that is, make the blades and screw for
the ruling pen and a spring or clamping tube for the pencil point.