GB621337A - Improvements relating to appliances for drawing ellipses - Google Patents

Abstract

621,337. Ellipsographs. GLADSTONE, D. M. Feb. 19, 1947, No. 4789. [Class 97 (iii)] Apparatus for drawing ellipses comprises a pair of straight-edged guide members 8, 9, Fig. 1, rigidly connected together at right angles to each other and preferably connected by a third member 10, the members 8, 9 having means such as pins 12, 14 provided on the corners of the frame for preventing their displacement when laid upon the drawing surface, and a trammel 15, Fig. 4, having a pair of depending pegs 18 adjustable lengthwise of the trammel and a holder for a marking instrument 19 also adjustable lengthwise of the trammel. The trammel 15 is provided with a longitudinal slot 16, preferably enlarged on the undersurface, to receive slide blocks 17 fitted with studs 24 and clamping nuts, each block carrying a peg 18 of concave shape to permit of closer movement towards the marking instrument. The marking instrument 19 is carried in a block 20 adjustably mounted on a longitudinal rod 21 clamped at one end in a block 22 which is secured to a spring plate 23 projecting from the end face of the trammel 15. Alternatively the marking instrument may be clamped in a slide block slidable in the trammel slot. In use the trammel 15 is placed across the members 8, 9 so that the pegs 18 engage the inside edges of members 8, 9. By moving the trammel from a position in which one of the pegs moves from point 12 to a position in which the other peg moves to the same point, the marking instrument will describe a quarter of an ellipse. The pin points 12, 14 are positioned so as to be in line with the centre line of the trammel slot 16 when the trammel abuts the appropriate edge and pin 12 defines the intersection of the major and minor axes of the ellipse, the pins 14 lying on these axes. The pegs may both be located on the same side of the marking instrument, when larger ellipses are to be drawn.