GB703754A - Improvements in t-squares - Google Patents

Abstract

703,754. Mathematical drawing-appliances. EVANS, W. J. Aug. 13, 1951 [Aug. 10, 1950; March 19, 1951], Nos. 19961/50 and 6553/51. Class 97(3) In a T-square the stock and blade are fitted together for relative sliding movement as well as relative pivotal adjustment and releasable means, e.g. frictional means or wedge means are provided operable consequent upon the sliding movement for permitting or preventing the pivotal adjustment. To this end one or more surfaces on the blade are adapted normally under spring pressure to birid frictionally on a complemental surface or surfaces on 'the stock or a tapered end on the blade' is adapted under spring pressure or manual action to cause intermediate elements to bind frictionally on a surface of the stock. As shown the arcuate bevelled end of the blade 8 is urged by a tensioned spring 12 against a circular chamfered wall 3a of the stock which comprises a base 1 having a part circular recess 3 with a central rotatable boss 5 which has projections outwardly there from two faces parallel with the straight edge of the blade and in rubbing contact with similar faces of a recess or slot 7 in the blade. The cover plate 2 is'fixed to the base 1 and has a recess conforming to the recess 3 in the base 1 so that the blade is maintained in frictional contact with the inner surfaces of both base and cover plate by the spring 12 forcing the blade against the surface 3a and .the inner rim of the recess in the cover plate. Circular holes in the base and cover plate receive discs 1b, 2b fixed at the two ends of the boss 5. These' discs are graduated for reading the angular displacement of the blade. The blade has two straight edges, viz. 8a for drawing lines at angles to the stock g from 0 to 90 degrees and 8b for drawing lines at angles 90 to 180 degrees during which the T-square is reversed. In an alternative construction the tapered end of the blade forces, by wedge action, two segmental frictional elements against the arcuate surface of the stock under the influence of the springs. The stock is formed with upper, lower and intermediate plates with a circular hole through them, the blade passing into such hole through a gap in the intermediate plate. In a modification of this alternative construction the spring is omitted and stops retain the blade in the hole in the stock. Specification 597,020 is referred to.