GB503102A - Improvements in or relating to draughting machines - Google Patents

Abstract

503,102. Draughting - machines. CONSULTANTS, Ltd., and TRYTHALL, W. C. Oct. 15, 1937, No. 28146. [Class 97 (iii)] Each link of the parallel link mechanism connecting a fixed head 4 and a work head 5 comprises an encased flexible band passing round pulleys at each end of the link, the casing being extensible to adjust the tension of the band. As shown, the fixed head 4 comprises a pulley fixed on a base 8, 9, rotatable on an axis 11, 13 formed by brackets 10, so that the links 1, 2 of the draughting-machine may be folded together in a position parallel to the top edge of the board and then turned through a right-angle to a position clear of the board. The base 8, 9 may be locked to the brackets 10 by locknuts 14 in such a position that the work head 5 exerts a pressure on the drawing surface. A pivotally mounted casing 15 encloses the fixed pulley and is connected to the upper casing 16 of the central mounting 3 by two tubular rods 17 which enclose a cable 19 passing round the fixed pulley and a pulley 18 pivotally mounted in the casing 16. The rods 17 may be screwed into the casings 15 and 16, right-hand threads being used at one end and left-hand threads at the other, so that rotation of the 'rods 17 causes relative movement of the casings 15, 16. Locknuts 20 are provided. In a modification turnbuckles having right and left-hand threads are inserted in the rods 17. The link 2 consists of a pulley 21 integral with the pulley 18 and enclosed in a lower casing 22, a pulley 25 pivoted in a work head casing 23, a cable 26 passing round the pulleys 21, 25, and tubular rods 24 enclosing the cable 26 and. holding apart the casings 22, 23. The weight of the machine is counterbalanced by a helical spring 28 attached at one end to the casing 23 and passing through one of the tubes 24 and partially round an adjustable ring 29 surrounding the double pulley 18, 21. A similar spring is fixed at one end to the casing 16, passes through a tube 17 and is partially wrapped round and fixed to an adjustable ring in the fixed head 4. The work head is provided with a handle 49 and coaxial locking nuts 43, 46, 48. The nut 43 co-operates with a sleeve 38 on the base plate 35 and a screw 42 on the clamping plate 41 to secure the scales 34, 34<1>, separately to the plate 35 in desired positions. The nut 46 co-operates with a sleeve 45 on a protractor disc 33 and the sleeve 38 to clamp the plate 35 and disc 33 together, a spring pressed ball 56 being provided to facilitate setting in certain predetermined positions. The nut 48 has a finger piece 55 and co-operates with a sleeve 47 on the pulley 25 and the sleeve 45 on the disc 3 to clamp the assemblage comprising the scales 34, 341, the plate 35, and the disc 33 to the pulley 25. '