Page:International Library of Technology, Volume 53.djvu/24

 9. The compasses must be handled in such a manner that the needle point will not dig large holes in the paper. Keep the needle point adjusted so that it will be perpendicular to the paper, when drawing circles, and do not bear upon it. A slight pressure will be necessary on the pen or pencil point, but not on the needle point. 10. The dividers, shown in Figs. 9 and 12, are used for laying off distances upon a drawing, or for dividing straight lines or circles into parts. The points of the dividers should be very sharp, so that they will not punch holes in the paper larger than is absolutely necessary to be seen. Compasses are sometimes furnished with two steel divider points, besides the pen and pencil points, so that the instrument may be used either as compasses or dividers. This is the kind illustrated in Fig. 12. When using the dividers to

space a line or circle into a number of equal parts, hold them at the top between the thumb and forefinger, as when using the compasses, and. step off the spaces, turning the instrument alternately to the right and left. If the line or circle does not space exactly, vary the distance between the divider points and try again; so continue until it is spaced equally. When spacing in this manner, great care must be exercised not to press the divider points into the paper; for, if the points enter the paper, the spacing can never be accurately done. The student should satisfy himself of the truth of this statement by actual trial.

11. The bow-pencil and bow-pen, shown in Fig. 13, are convenient for describing small circles. The two points of the instruments must be adjusted to the same length: