GB742649A - Improvements in or relating to the plotting and ruling of circular and non-circular arcs - Google Patents

Abstract

742,649. Ruling curves. LINES, L. Aug. 26, 1953 [Aug. 29, 1952], No. 21737/52. Drawings to Specification. Class 97 (3). Apparatus for use in ruling curves comprises a template having several ruling edges some of which form the boundaries of slots in the template and are in the form of parts of logarithmic spirals having certain specific values of a number m, which defines the rate of change of radius of curvature, such that if any are of a ruling edge is selected so that the radii of curvature at its extremities are in the ratio of 2 : 1 then the tangents to its extremities are inclined to each other at an angle 180/a<SP>m</SP> degrees where a is a constant for all the edges. The specific values of the number mare 1, 1.5, 2 &c. and the appropriate value is engraved on the template adjacent each ruling edge. At various points along each ruling edge there may also be numbers defining the radius of curvature at each such point. A plurality of linear scales may be engraved on the template for constructing a curve approximating to an ellipse having known semi-axes, each scale having as its inert k the value of that of a standard scale, the value of k being different for each scale. Parabolic ruling edges so shaped as to enable arcs of small radius to be ruled may be provided, as also may ruling edges in the form of circular arcs having radii such that if these edges are used to rule a series of arcs with a common chord, the arcs will intercept substantially equal lengths on the perpendicular bisector of that chord. A second template having similar ruling edges may be provided for use in conjunction with the first template.