GB767313A - Improvements in or relating to means for controlling the movements of elements so that they describe arcs of large radius - Google Patents

Abstract

767,313. Curve-describing instruments. COOK, K. E. J. June 29, 1955 [March 29, 1954], No. 9049/54. Class 97(3) A compass like instrument has a locating leg with a fulcrum device at its foot providing a fulcrum line about which the locating leg can rock a scribing leg, and a hinge device connecting the two legs together providing a hinge axis obliquely disposed relative to the fulcrum line, the axis and the fulcrum line being contained in a common plane, whereby the scribing leg is caused to describe an arc on a plane surface when swung about the hinge axis away from or towards the locating leg, the latter rocking on the fulcrum line during the swinging movement. As shown in Figs. 2 and 3, the device comprises a locating leg a and a scribing leg b. The locating leg a terminates in a blade d, which may be placed on the drawing paper and allows the leg to rock about the edge of the blade. If desired. the blade member d may have needle points f to assist in locating it on the paper. The scribing leg b has a conventional marking point p, and at its other end there is a circular scale bearing member j. The legs a and bare connected together at their upper ends by a hinge member, see also Fig. 5. One part of the hinge c<SP>1</SP> has a screw threaded member c<SP>6</SP> projecting through a hole in the scale bearing member j which is clamped to the hinge member by means of a nut c'. The other hinge member c<SP>2</SP> is pivoted about a longitudinal axis in a recess in the member c<SP>1</SP>, and has a screw threaded hole c<SP>9</SP> which receives a screw c<SP>8</SP> passing through a hole. in the upper end of the leg a. To set the device, the screw c<SP>8</SP> and the nut c<SP>7</SP> are slackened off, and the hinge is ad-. justed by means of the scale on the plate j so that its axis intersects the line of the knife edge d at a point which is the centre of the arc which is to be described. The nut c<SP>7</SP> and the screw. c<SP>8</SP> having been tightened again, the marking point p is moved away from its initial position close to the blade d. The point will then trace out the arc of a circle as required. In another example, the hinge is modified in such a manner that the point may be initially in line with the edge of blade d, and may be removed away therefrom in either direction. In a further modification, the marking point p is replaceable by a second blade similar to the blade d. When the instrument is closed, the blade on the leg b will come to lie.against or in alignment with the blade on the leg a. The latter may then be swung away from the leg b which will rock upon the fulcrum provided by its blade (fitted with needle points if desired), and when the knife edge and points of the leg a are disposed a suitable distance from the blade on the leg b they may be pressed down upon the drawing board to provide a new fulcrum line for describing an arc in continuation of the arc previously described by the scribing marking point p. According to the Provisional Specification a modified arrangement has a second knife edge and points, and the pencil point is brought into operating position when the second knife edge is swung out of operating position. The additional knife edge enables the first blade to be shifted to enable the curve to be extended. The Provisional Specification also refers to the application of the device to television and kinematograph cameras