to step off a series of equal distances, and to divide
lines into a number of equal parts.
Drop Bow Pen
The DROP BOW PEN (fig. 2-16D) is not one
of the standard instruments. However, for some
jobs it is essential. It is used to ink small circles
with diameters of less than a quarter of an inch.
As the name indicates, the pen assembly is free
to move up and down and to rotate around the
main shaft. When using this instrument, hold the
pen in the raised position, adjust the setscrew to
give the desired radius, and then gently lower the
pen to the paper surface and draw the circle by
rotating the pen around the shaft.
Maintenance of Compasses and Dividers
Figure 2-17 shows the three shapes in which
compasses and dividers are made: round, flat, and
bevel. Figure 2-18 shows two types of pivot joints
commonly found on compasses and dividers.
When you select compasses and dividers, test them
for alignment by bending the joints and bringing
the points together. New instruments are factory
adjusted for correct friction setting. They rarely
require adjustment. A small jeweler’s screwdriver
or the screwdriver found in some instrument sets
(fig. 2-15H) is used for adjusting most pivot joint
instruments. Instruments that require a special
tool should be adjusted by skilled instrument
repairmen.
Pivot joint compasses and dividers should be
adjusted so that they may be set without undue
friction. They should not be so rigid that their
45.158X
Figure 2-17.-Shapes of compasses and dividers: (A) Round;
(B) Flat; (C) Bevel.
142.34X
Figure 2-18.-Sections of pivot joints.
manipulation is difficult, nor so loose that they
will not retain their setting.
Divider points should be straight and free
from burrs. When the dividers are not in use, the
points may be protected by sticking them into a
small piece of soft rubber eraser or cork. When
points become dull or minutely uneven in length,
make them even by holding the dividers vertically,
placing the legs together, and grinding them lightly
back and forth against a whetstone. (See fig. 2-19,
view A.) Then hold the dividers horizontally and
sharpen each point by whetting the outside of it
back and forth on the stone, while rolling it from
side to side with your fingers (fig. 2-19, view B).
The inside of the leg should remain flat and should
not be ground on the stone. The outside of the
point should not be ground so that a flat surface
results. In shaping the point, be careful to avoid
shortening the leg.
Needles on compasses and dividers should be
kept sharpened to a fine taper. When they are
pushed into the drawing, they should leave a
small, round hole in the paper no larger than a
2-14
