Patent GB-190315688-A (GB)
Title: Improvements in Drawing Appliances.
Inventor: ROBINSON HUGH CECIL
Filed: 1903-07-15
Granted: 1904-05-26
Abstract: 15,688. Robinson, H. C. July 15. Curves, figures, &c., plotting and reproducing.- Relates to an instrument for making perspective drawings from plan drawings or both perspective and plan drawings simultaneously, including means for drawing straight lines and circles in plan and perspective. The plan is drawn or traced on the flat surface or drawing board A by a point at C on a slide 7, sliding on a bar 4 fixed to a plate 51 pinned to a slide 9, which may be slid or clamped on a bar 11 ; a block 10 also slides on this bar, which is attached to a fixed frame 41. To this frame, a board T is hinged at X X and in front of this frame the bars 1, 2 pivotally attached at the slides 9, 10 may slide, the bar 1 moving with the bar 4, while the bar 2 is moved by means of a pivoted slide-block 61 on the bar 5, one end of which is pivoted to the slide 7 at point C, and the other is guided by a slide 90, pivoted at the point of sight P. The bar 2 carries a slide 16 to which the pencil, for drawing the perspective plan on the board T, is attached, and pivoted to the slide 16 is a slide 14 working on a bar 3, pivoted horizontally at the vanishing-point at 17, and carrying another slide 13 pivoted to a slide 15 clamped to the slide 1 by a lever 49 at a height depending on the height of the plan above or below the vanishing point. After setting the instrument, by placing the point C above any point in the plan on A, the position of that point, in the perspective drawing on T, is indicated by the point of the pencil fixed to the slide 16. The movement of the point C may be guided by rulers or otherwise, but, for drawing straight lines parallel to the slide 4, a screw is provided immediately below the rod 77, working in a nut fixed to the slide 7, and turned by a removable handle at the outer end of the bar 4, which rests on a rail 45 parallel to the slide 11. Bevel-wheels, immediately below the wheels 33, 34, may transmit motion through a clutch to a nut turning in a bearing on the slide 9, and gearing with a screw 68 of such a pitch that the simultaneous movements of the slides 7, 9 cause the point C to trace a line perpendicular to the slide 4. In drawing the plan and perspective view of a circle in a vertical plane parallel to the .bar 4, adjustable pins on the discs 20, 21 are set to the radius of the circle, the disc 20 being mounted on a bearing on the hinge piece of the bar 1, and the disc 21 on a bearing on the piece 51, both discs being driven by mitre gearing and a shaft 77, at the same speed. The pin on the disc 21 works in a vertical slot at the end of a horizontal sliding bar 27, which is then clamped to and moves the slide 7. The pin in the disc 20 moves the slide 15 through a vertical sliding bar 26 in a similar manner. By making the radius of the pin on the disc 21 equal to the radius of the required circle multiplied by the co-tangent of the angle, preferably 60‹, between the slides 4, 11, the perspective of a circle, in a vertical plane at right-angles to the bar 4, may be drawn. For drawing the perspective of circles in the horizontal plane, the bar 26 is thrown out of action, the slide 15 being fixed at a suitable height, and a horizontal bar 85, moved in a similar manner to the bar 26 from the same pin, is clamped through pivoted clamps 78 to the guide-bar 11, the slide 9 thereby being reciprocated. The pin on the disc 21 is set to the radius of the required circle, and the pin on the disc 20 to the radius of the circle multiplied by the cosecant of the aforesaid angle. The line joining the point of sight P and the vanishing-point at 17, when the board T is vertical, is made parallel to the slide 4.