GB661980A - Improvements in or relating to drawing instruments - Google Patents

Abstract

661,980. Pantographic apparatus. BELL, L. H., BAINBRIDGE-, and BUCKINGHAM, J. March 28, 1950 [March 9, 1949], No. 6400/49. Class 97 (iii). A pantographic linkage with which a drawing may be reproduced with a change of scale along one of two rectangular axes, e.g. for drawing an ellipse from a circle, for redrawing a graph curve with a change of scale along one axis only, or the reproduction of a drawing with dimensions fore-shortened in one direction to give an impression of perspective and facilitation of isometric projection by reduction along one axis in the ratio of 3 to 1, has no fixed point but has means to constrain a point on a line through the tracings and drawing points to move, in the plane of the linkage, only perpendicularly to said line. As shown, an interpivoted four link pantograph has a point C on the line connecting the drawing point D and tracing point T, and a second point C<SP>2</SP> constrained to move along a straight track rail 7 secured firmly to the drawing board at right angles to the line D, T, and the constrained points c, c<SP>2</SP> and the tracing point T (or the drawing point D) are equidistant from the common pivot p<SP>2</SP> of the links. Each of the follower members provided at c and c<SP>2</SP> comprises a block 9, Fig. 2, having a pintle 10 and a pair of ball bearings 11 inclined so that their outer races rest as wheels on the rail 7. Smooth feet 12 and 13 are provided on arms 3 and 1 to limit rocking and adjustable balance weights 15 on arms 2 and 3 are provided to adjust the poise on the rail 7. The use of a straight line track may be avoided by a combination of Peaucellier cell linkages. In an alternative arrangement the constrained point C 2 may be located on the arm 2, and then the arms c<SP>2</SP>, p<SP>1</SP>; c, p<SP>1</SP> and D, p<SP>1</SP> must be equal. To avoid lateral inversion of the drawing produced by the arrangement described, the common point p<SP>3</SP> is used as the drawing point and the free end of one of the long links 1, 2 is used as the constrained point c. The second constrained point being on the arm 1 as at c<SP>2</SP>, Fig. 1, or on the prolongation of the arm 3.