The practical draughtsman's book of industrial design and machinist's and engineer's companion : forming a complete course of mechanical, engineering and architectural drawing . a tracer round its boundary;and, besides the advantage of not injuring the drawing, it pos-sesses that of speed and accuracy. A frame, a, carries an axle,which has on it two rollers, b, of equal size, and a cone, c. Itis heavy, so that it maintains its parallelism on being pushedalong the paper. The sides of the frame are parallel to the edgeof the cone, and are fitted to receive the circumference of fourfriction rolle
The practical draughtsman's book of industrial design and machinist's and engineer's companion : forming a complete course of mechanical, engineering and architectural drawing . a tracer round its boundary;and, besides the advantage of not injuring the drawing, it pos-sesses that of speed and accuracy. A frame, a, carries an axle,which has on it two rollers, b, of equal size, and a cone, c. Itis heavy, so that it maintains its parallelism on being pushedalong the paper. The sides of the frame are parallel to the edgeof the cone, and are fitted to receive the circumference of fourfriction rollers, k, which move along a, and carry a light frame, f,terminating on the tracing-point, p, to which the handle, h, isattached by a universal joint. The frame, f, also carries a wheel, i,which, by means of a weight, is pressed on the surface of thecone, and receives motion from it as the tracer is carried along the paper. The index-wheel, i, only touches the cone by a narrowedge, the rest of its circumference being of smaller diameter, andcontaining a silver ring divided into 200 parts, which are againsubdivided by a vernier into 2,000 parts. The value of each of Fig. these divisions is the T J5th part of a square inch ; so that one turnof the wheel represents 20 inches. Another index-wheel, T,moved by i, is divided into five parts, each of which represents20 inches, so that a complete revolution of T values 100 eye-glass, e, assists in reading the divisions and vernier. It is apparent, from the construction of this instrument, that ifthe tracer be moved forward, it will cause the index to revolve,not simply in proportion to that motion, but in proportion to themotion of the tracer, multiplied by the distance of the edge of theindex-wheel, from the apex of the cone ; and that the revolvingmotion of the index will be positive or negative, according as thetracer is carried backwards or forwards. Hence, if the tracerbe carried completely round the outline of any fig
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Keywords: ., bookcentury1800, booksubjectarchitecturaldrawing, booksubjectmec
