GB535699A - Improvements in and relating to drawing apparatus - Google Patents

Abstract

535,699. Drawing-apparatus. EVANS, W. J. Oct. 13, 1939, No. 27810. [Class 97 (iii)] In a drawing apparatus of the type in which a straight edge is movable parallel to itself across the drawing board a driving mechanism is provided to move the straight edge in a series of steps each of predetermined amount. The straight edge 50, Fig. 1, mounted in suitable guides, is connected to a rod 14 upon which is mounted a block 13. The latter block is arranged to slide on the rod or to be clutched thereto by the driving mechanism which also advances the block 13 together with the rod 14 and straight edge an amount determined by the adjustable stops 32, 34, Fig. 2, while during the return motion the rod 14 is declutched and permits the block 13 to be retracted for another advance step. The driving mechanism as shown comprises a pedal 52, Fig. 2, bell crank lever 56, counterpoise 53 operating a bell crank 54 mounted on the block 13. The first movement of the bell crank 54 operates through lever 21, Fig. 2, a clutch comprising a boss 22, Fig. 4, and a split ring 23 having a ball 25 in a radial slot 24. The boss 22 is eccentric to the rod 14 and therefore rotary movement causes the ball 25 to press the ring 23 into frictional contact with the rod 14. Continued movement of the driving mechanism then carries the rod 14 forwardly together with the straight edge 50. On return movement the rod is declutched. Specifications 139,764, [Class 97 (iii)], 476,586, 485,146 and 535,698 are referred to.