(marking tool), an instrument used in laying out workpieces to scribe lines, center punch, measure lengths, and mark off sections, angles, and circles.
Scribers, which are equipped with a point that has been sharpened and hardened, are among the tools most often used for scribing lines along a straight-edge or try square. Center punches, equipped with a hardened head and a hardened and sharpened point, are used for center punching—making indentations on lines already marked off in order to preserve the layout until the work is completed; the indentations are made by striking the head of the center punch with a light hammer. Dividers are used for marking off circles, arcs, sections, and various geometric figures and for transferring dimensions from a ruler to the workpiece.
Perpendicular lines are scribed using a try square; try squares equipped with a base are the most stable and the most frequently used. Oblique lines are marked off by means of a bevel protractor. A trammel is used for marking the precise division of straight lines and for marking off centers and circles with large diameters.
The principal tool used for laying out in three dimensions is the surface gauge; it is used to mark off parallel vertical and horizontal lines and to check the mounting of the workpiece on the layout plate. A surface gauge equipped with a micrometer screw and a height gauge is used for marking off with greater precision and for measuring. Various types of center squares are used for locating the centers of circles.
N. A. SHCHEMELOV