GB1321790A - Drawing apparatus - Google Patents

Abstract

1321790 Mathematical drawing appliances H P GUNTHER 11 April 1972 16695/72 Heading B6P [Also in Division G1] A drawing appliance comprises two mutually perpendicular arms 1, 2 having linear scales 7, 8, 14 thereon, a protractor 3 connected to at least one of the arms, a cursor 4 slidable along the arm 1 and having a hole 5 therethrough into which the drawing tip of a drawing instrument may be inserted, and two holes 11, 12 in the arm 2, similar to the hole 5 and positioned so that an edge of the arm 1 lies along the perpendicular bisector of the line joining the two holes 11, 12. Cylindrical bosses 13 are provided coaxial with the holes 11, 12. Circular holes 10 of known radius are provided in the arm 2. Except for the cursor, the appliance is in one piece, of transparent or translucent plastics or sheet metal. To locate the centre of a circle, the holes 11, 12 are placed on the circumference of the circle and a line drawn along the inside edge of the arm 1. This is repeated for another position of the appliance, the intersection of the two lines giving the required centre. The centre of a cylindrical shaft may be found similarly, using the appliance on the shaft end face and bringing the bosses 13 into contact with the shaft periphery. To draw a circle, a pin is placed in the hole 11, the cursor 4 is set to the required radius on scale 14, which has its zero at the hole 11, and rotating the appliance about the centre-location hole 11 with a drawing tip through the cursor hole 5.