. The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion: forming a complete course of mechanical, engineering, and architectural drawing. . oden bar, or ruler,T, of considerable length, and of a T section, beingformed of two strips united by a dovetail construction prevents warping or bending,and is necessary where a scale is cut on the bar, asany deviation from a straight line would render themeasurement inaccurate. The compasses are pro-vided with a pen, or pencil leg, and a centre leg,these being fitted upon the bar with socket pi
. The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion: forming a complete course of mechanical, engineering, and architectural drawing. . oden bar, or ruler,T, of considerable length, and of a T section, beingformed of two strips united by a dovetail construction prevents warping or bending,and is necessary where a scale is cut on the bar, asany deviation from a straight line would render themeasurement inaccurate. The compasses are pro-vided with a pen, or pencil leg, and a centre leg,these being fitted upon the bar with socket pieces,M, in. These socket pieces are fixed at any pointalong the bar, by pinching screws at the side; butto prevent the point of the screw from injuring thebar, a loose plate of metal is interposed next to thebar, as shown in the section, fig. 24. The socket,M, is in a solid piece with its pen, or pencil-holder ; but the centre leg, n, is in a separatepiece from its socket, m, and is capable of minuteadjustment back or forward in the latter. Thesocket, M, has a cylindrical groove along its under side, in whichslides the head of the leg, n. This head is formed with a Fig. 23. Fig. horizontal screw passage, or nut, to receive the screw spindle,I, which is held by an eye at the end of the socket groove,and is actuated by means of a button on tlic outside. By 190 THE PRACTICAL DRAUGHTSMANS turning the screw, i, in either direction, the centre leg may beadjusted with great accuracy at any part of the socket. Inadjusting the instrument to any measurement, the pencil socket,M, is loosened, and set pretty near the mark, and fixed; theexact length of radius is then obtained by adjusting the centre legby means of the screw. A pair of beam compasses, or dividers, ofsomewhat different description, are represented in side elevation infig. 25. In tliis instrument, which is entirely of metal, the centre Fig. 25.
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Keywords: ., bo, bookcentury1800, bookdecade1850, booksubjectmechanicaldrawing
