GB702594A - Improvements in drawing equipment - Google Patents

Abstract

702,594. Mathematical drawing instruments. KROSLAK, H. Feb. 6, 1950, No. 2977/50. Class 97(3) A T-square head having a ruler fixed or angularly adjustable with respect thereto which is movable along a guide-way or groove in a drawing board is fixed at a desired point along the groove by means of two clamping jaws capable of relative sliding movement towards or away from each other, one of the jaws consisting of a flange on the head engaging freely in the groove and the other consisting of a flat slider which either engages in the groove or with the external edge of the drawing board, the clamping pressure of both jaws being exerted by turning a lever rotatably mounted within and on a pivot secured to the head and is provided with an eccentric hub part which on operation of the lever actuates the slider jaw. As shown in Figs. 2 and 3 the flanges 11a, 11b of the head 4 carrying ruler 5 fixed with respect thereto and the flange 12 of a slider 10 carried by the head all engage freely in the groove 2 of the board 3. A lever 6 is pivotally mounted in a casing 9a of the head on an eccentric pivot 17 and is connected to the slider 10 by a link 15 pivotally connected by pin 14 to the slider and by pin 16 to the lever 6. Rotation of the lever 6 from the broken-line position shown in Fig. 2 to the full-line position until the pins 14, 16 and 17 are in a straight line cause the flanges 11a, 11b and 12 to move apart and extend pressure on the sides of the groove. As shown in Figs. 5 and 6 a jaw 28, Fig. 6, is forced against the pressure of a spring 29, Fig. 6, against the edge of the board 3, Fig. 6, by a lever 6 having a cam-shaped end 27 and rotatably mounted on a cylindrical guide 26 on the casing 24 of the head 4 and concentric with a hollow journal 20 secured to the ruler 5 so that rotation of the lever 6 to press jaw 28 against the external edge of the board causes the flange 11, Fig. 6, to be drawn against the outer edge of the groove 2. A second lever 23, Fig. 5, is provided for fixing the angular position of the ruler 5 and is secured at its end to a ring 22 bearing against the lower end of a dished portion 18 of the head 4 and is internally threaded to co-operate with external threads on the journal 20 so that on rotation of the lever 23 and ring 22 the journal 20 with the ruler 5 rotatably attached thereto is drawn down pressing the ruler against the head 4. The journal is prevented from rotation by a pin 21 passing therethrough into slots in the dished portion of the head. In an alternative construction for fixing the angular position of the ruler the lever 23 is provided at its end with a wedge-shaped portion which on rotation of the lever secures the ruler to the head by wedge action.