GB714010A - Improvements in draughting machines - Google Patents

Abstract

714,010. Draughting-machines. CHAUVELON. A. J. F. June 25, 1952, No. 15938/52. Class 97(3) A draughting machine has a head which comprises three co-axial rotary plates of which the first plate carries straight edges and is fixed to a manually rotatable spindle and is coupled to the second plate, which is freely rotatable about the spindle, by projections provided on one of these plates and spring urged into recesses in the other plate enabling relative stepwise rotation of the first and second plates, while the second plate cooperates with the third plate also freely rotatable about the spindle by a friction clutch which may be coupled and released by means comprising a manually adjustable lever and a cam ring, this cam ring having recesses disposed to set resiliently seated bases, movable between the recesses by said lever, in either of two axially distinct positions corresponding to coupling and release of the clutch, whereby the first plate is rotatable relative to the third plate stepwise when the clutch is coupled and freely when the clutch is released. The machine head shown is connected by a parallel linkage to a bracket for attachment to a drawing board and comprises a first plate 14 to which three mutually perpendicular straight edges are frictionally secured, this plate being fixed to a spindle 22 having an operating knob 23 and a scale 24 cooperating with an index 25 on the third plate 26 to which links 4,5 of the parallel linkage are pivoted on conical pins 27, 28 which are received in recesses in a plate 29. Plates 26, 29 are freely rotatable on spindle 22. Between plate 29 and the third nlate 31, provided with spaced conical recesses 32 for engagement with spring loaded balls 33 on plate 14, is a friction disc 30. This disc is pressed downwardly by spring 42 on to the balls 33 so that plate 14 can only rotate relatively to plate 26 in steps, when a lever 38 carrying balls 39 for engagement in openings in a fixed cam ring 43 is rotated so that balls 39 engage with the openings 45, Fig. 5, in the tops of inclines on the ring 43. When the balls 39 engage with openings 46 in the bottom of the inclines, the friction disc is released and plate 14 can rotate freely.