Patent GB-714679-A (GB)
Title: Improvements in or relating to drawing apparatus
Inventor: DEAKIN THOMAS MEYRICK
IPC: B43L13/14
Filed: 1951-02-02
Abstract: 714,679. Perspective drawing appliance; curve-describing instrument. D. R. W., Ltd. Feb. 1, 1952 [Feb. 2, 1951], No. 2693/51. Class 97(3) Perspective drawing apparatus comprises a tracing point displaceable in three dimensions and a drawing point movable in two dimensions, the tracing point being coupled to the drawing point through at least one universal pivotal connection and at least one transversely rigid telescopic or longitudinally slidable member which is universally pivotally mounted at a selected viewing point, the plane of movement of the drawing point being inclined (preferably at 90 degrees) to the viewing axis and the said coupling being such as to constrain the drawing point to have a displacement proportional to the component, in a plane parallel to the drawing plane of the displacement, of the tracing point. One form of perspective drawing apparatus comprises a tracing bar 4. Fig. 1, connected by ball and socket joint 1, 2 with a part 3 that is movable vertically in a fixed slide 6 and by ball and socket joint 9, 10 with a pantograph 12 which is connected to a drawing point 14. The bar 4 ends in a tracing point 5 which moves over the contours of an object or plan view thereof and transmits such movement to'the drawing point so that a perspective view of the object is obtained on a drawing surface 15. When a plan view of the object is provided, it is placed on a table 8 which is inclined to the plane of the surface 15 and is reciprocable through a distance corresponding to the third dimension of the object. The pantograph is adjustable to vary the scale of the drawing. In another form, Fig 3, the tracing bar 4a and the drawing bar 4b comprise telescoping parts forming a parallel linkage. The bars are pivoted at 21, 22 to a cage which is pivoted at 24 to the frame 3 about an axis normal to the axes of the pivots 21, 22. The bars 4a, 4b are connected by ball and socket joints 9, 10 and 19, 20 to tracing and drawing points 5, 14 carried by saddles 29, 46 which are slidable along straight edges on a table 8 and drawing surface 15. Table 8 is rotatably and slidably mounted in a bracket 26 which is itself movable over an arcuate path 27 having its centre of curvature at C. In order to trace circles of small radius, the saddle 29, Fig. 5, carrying the tracing point 5 is clamped to a straight edge 30 attached to a slide 32 which may be clamped at 34 to a slide 33 movable in one direction over a guide 35 which is slidable in an orthogonal direction over a fixed guide 36. Slide 33 is connected by an arm 37 with a member 39 which is slidable in a diametrical groove 40 in a disc 41. This disc is pivoted to a slide 42 which is movable in the direction of slide 33 along a guide 44 which is itself movable in an orthogonal direction over a fixed guide 45. The slides 42, 44 are moved until the distance of the member 39 from the pivot of disc 41 is equal to the radius of the circle to be drawn. The member is then clamped in the groove 40 by clamp 38 and slide 32 is clamped at 34 to slide 33. If disc 41 is now rotated, the tracing point 5 traces out the original circle. Another form is described in which the tracing bar is replaced by a telescope, movable to follow the outline of a building or other large object; in this case, the telescope axis constitutes the tracing bar and each focused point becomes a tracing point.