In making this spring, we take a piece of steel about two and one-fourth inches long and of the same width as the leg of the divider, and attach it to the inside of the leg as shown at Fig. 14, where _D_ represents the spring and _A_ the leg of the dividers. The spring _D_ has a short steel tube _C''_ and set-screw _d''_ for a fine point like _B_ or _B'_. In the lower end of the leg _A_, Fig. 14, is placed the milled-head screw _g_, which serves to adjust the two points of the dividers to very close distances. The spring _D_ is, of course, set so it would press close to the leg _A_ if the screw _g_ did not force it away.
SPRING AND ADJUSTING SCREW FOR DRAWING INSTRUMENTS.
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.