GB635805A - An improved tacheometric staff - Google Patents

Abstract

635,805. Surveying - instruments. COOKE, TROUGHTON, & SIMMS, Ltd., TAYLOR, E. W., and HOGG, F. B. R. Feb. 4, 1948, No. 3307. [Class 97 (ii)] In order that a tacheometric staff may be set normal to the line of sight of the observing instrument, the mounting for the staff is provided with means for orientating the staff and with sighting means having a line of sight normal to the face of the staff when secured to the orientating means for sighting on to the objective of the observing instrument. Preferably the staff is detachably secured to the mounting in positions which are normal to each other. The mounting comprises an L-shaped bracket 3, Fig. 3, provided with a vertical spigot 6 in its lower portion by means of which it may be secured to a tripod and around which the mounting and staff may be rotated in azimuth by a worm drive 16, 17 operated by knobs 16<SP>1</SP>, Fig. 4, and having an upstanding portion provided with bearings 2, 21 for a horizontal spindle 9 which may be rotated about its axis by a worm 14 and sector 12 operated by knobs 14<SP>1</SP> and housed in the upstanding portion. One end of the spindle 9 is provided with a head 23 having a wedge-shaped protuberance 23b on its outer vertical face adapted to engage a similar shaped block 28 on the staff grip 30 when the staff 1 is to be mounted in a horizontal position and a second wedge-shaped protuberance 23a on its upper horizontal face to engage the block 28 of the staff when mounted in a vertical position. In either position the staff is clamped to the head by means of a spring-urged clamp 24 operated by knob 25. A counterweight 22 is adjustably secured to the other end of the spindle 9. The sighting means by which the staff is positioned normal to the observing line of sight comprises a telescope 39 mounted on the side of the head 23 normal to the two protuberances 23a, 23b and adapted to sight the objective of the observing instrument through apertures 39a in the opposite face of the cube and 1a adjacent the zero of the scale in the end of the staff. The mounting may be levelled by a bubble level 50. The staff, Fig. 7, has a longitudinal V-shaped groove 37 to receive the scale 38 and this groove is widened at the bracket end to take the vernier 38<SP>1</SP> which together with the scale 38 butts up against the adjacent end protector plate 35, all being secured to the clamping bracket 29 on which is secured the block 28. The scales are preferably made of materials with low temperature coefficients of expansion.