Making Scale Enlargements with a Rubber Band
For reducing or enlarging maps, and similar drawings of irregular design, the device shown in the illustration will replace the ordinary instruments, and enable the draftsman to turn out a given amount of work in much less time than required when proportional dividers are used. The materials needed are an eraser, a rubber band, two pins, two thumb tacks, and a few drops of rubber cement. From the eraser two pieces are cut, as shown in the sketch, about ¹⁄₄ by ¹⁄₂ by 1¹⁄₄ in. Cut deep slits in each end of these pieces. Insert the end of the rubber band, cut at the splice, in one of these slits and place a thumb tack in the other. A pin is thrust through the eraser and trimmed close, to prevent the thumb tack from tearing the eraser. Cement the slits with rubber cement, and place the assembled device under a book weight, until the cement has set.
This Simple Device Is Useful in Enlarging or Reducing Drawings and Maps
Assuming that a contour map is to be enlarged, the rectangular divisions of the original map, ordinarily section lines or the boundaries of quarter sections, are drawn on the larger sheet as a base for the reproduction. Place the device on the original map, as indicated, the edge of the rubber band touching a “horizontal” section line between two “vertical” ones, the rubber band under slight tension. On the black surface of the band, dot white points, with water color, along the section line at which the contour lines intersect it. Also place a dot at each end of the band to indicate the position of the two “vertical” section lines between which the band is set.
Transfer the device to the same relative position on the enlargement, stretching the rubber band. Make dots at each end, denoting the “vertical” section lines, for the corresponding lines on the enlargement. The series of intermediate points along the band will be in the same relative position on the enlargement as they were on the original. They can be connected on the enlargement with as accurate a result as obtained by the use of proportional dividers, and more rapidly.
After the points are indicated upon the enlargement, the reproducing device is removed and the surface of the rubber band cleaned instantly by touching it with a moist cloth. The exposed part of the rubber band is a variable, and the device can be made with this dimension adapted to the work. It is capable of enlarging or reducing at a ratio not greater than six to one, above which the rubber band approaches its elastic limit.—H. L. Wiley, Seattle, Wash.