GB728352A - Apparatus providing an adjustable scale suitable for the preparation of, and for usewith, perspective drawings - Google Patents

Abstract

728,352. Perspective drawing apparatus. NORTH THAMES GAS BOARD. Sept. 16, 1953, No. 25658/53. Class 97 (3). Apparatus for the preparation of perspective drawings and the measurement of true linear dimensions therefrom comprises a base plate and an operating arm, the base plate having a scale and straight lines joining equidistant points thereon to a point on a normal to the scale, the operating arm being adapted to be positioned relatively to the scale by translational and angular movement and having a reference line or edge adapted to be viewed superimposed upon and intersecting the straight lines on the base plate, the intersection of said reference line with said normal constituting a zero point. The form shown comprises a base 1 at the upper edge of which is a lug 3 and an elongated lug 4. An arm 14 is pivoted to the lug 3 and carries a locking screw 19 guided in an arcuate slot 17 in the lug 4. A protractor scale 18 indicates its angular setting. Another arm 20 is connected to the arm 14 by pivoted links 24, 25 to form a parallelogram. The arm 14 carries a slide 28 having a projecting lug 29 with its under surface in the same plane as the under surface of the base 1. The slide also carries a graduated cross arm 31. A slide 30 slides on both the arms 20 and 31 and carries a transparent projecting lug 32. The lugs 29, 32 have marking-off edges 33, 34 in line. The arm 14 carries a slide 36 which can be secured thereto by a screw 39 and carries a projecting lug 37 with a marking- off edge 38 which may be brought into contact with the edge 33. A transparent arm 9 is coupled to slide along the arm 20 by clips 21 and may be secured by a screw 23. The arm 9 is obscured along its upper edge by a band of paint 10 to provide a reference line 11. The arm also carries a measuring scale 12 with its zero opposite a pin 13 lying in the line 11. The pin 13 engages a slot 2, in the base 1, normal to the longitudinal edges thereof. The base is inscribed with straight lines 6 radiating from the pin 13 engages a slot 2, in the base 1, normal to the longitudinal edges thereof. The base is inscribed with straight lines 6 radiating from the upper end 7 of the slot 2 to equidistant points on a scale 5 parallel to the edge of the base. The use of the instrument is described in detail in the Specification.