GB364025A - Improvements in drawing-compasses - Google Patents

Abstract

364,025. Beam compasses. THOROLD, A. J., 6, Hereford Road, 'Bayswater, London. Sept. 25, 1930, No. 28771. '[Class 97 (iii).] In a beam compass, an operative point is adjustably mounted on a head-piece, slidable along the beam and optical means by which the position of the point itself relative to the sliding head may be observed are provided. In the form shown a beam made in interlocking sections 1a, 1b, 1c carries the sliding heads 2, 3. The beam comprises a pair of splines 4, 5, Fig. 4, which are respectively recessed for reception of a graduated tape 6 and provided with notches 7 for positioning the sliding heads on the beam. The tape 6 which may be interchanged as desired is secured at one end to a tab 6a of thicker section which is fastened to the beam by a screw 9, the other end being carried by a spring reel 10 secured to the beam by a clip 11. A micrometer screw 13 for adjusting the sliding head 2 has secured to it by the clamping screw 16 a detachable disc 15 preferably graduated in accordance with the graduations on the tape 6 being used. The sliding head 2 carries a handle 20, a clamping screw 21 and a holder 22 carrying the point 26 and adapted to slide on the head 2 by operation of the knurled nut 23. The sliding head 3 is provided with a clamping screw 27, a slidable point holder 28 with adjusting nut 29, and a pair of housings 32, Fig. 6, into either of which in accordance with the series of notches 7 to be used may be placed a plunger 33 pressed against the notches by a spring-urged pivoted lever 35. The sliding head 3 is provided with a sighting tube 40 focused on the point 31, the latter being correctly set relative to the head 3 when it is adjusted to coincide with cross wires in the sighting tube 40.