GB571458A - Improved variable electrical resistance - Google Patents

Abstract

571,458. Variable-contact resistances. MORGAN CRUCIBLE CO., Ltd., and MILLER. L. W. Feb. 22, 1944, No. 3306. [Class 37] A variable resistance, particularly for volume control in radio reception and as a midget type control on aircraft, is constructed so as to withstand extreme conditions without undue variation. The casing comprises a part 1 and a part 3 carrying the segmental strip resistance element 4, the rotor contact 5, and terminals 6, 8. The part 3 of the casing is made of synthetic plastic material, whilst the other part 1 is of aluminium or aluminium alloy and is formed with an integral boss 11 providing a bearing for the operating spindle 2. The two parts 1, 3 are secured together by spinning the rim 13 of the part 1 over a flange 14 on the part 3 after inserting a sealing ring or washer 15. The spindle 2 carries a contact operating member 9 of synthetic plastic material moulded on a metal piece 16. This has an axial hole 17 into which is forced a knurled part 19 on the reduced end of the spindle 2, a groove 18<1> being provided into which the metal piece 16 is swaged. The spindle is fitted in an annular recess 20 with sealing rings 21 to make the bearing in the bush fluid-tight. The member 9 is formed with an extension 22 adapted to abut against a projection 23 in the part 1 to limit the rotation of the spindle. The rotor contact comprises a flat metal ring 24 indented to form a projection 5 for bearing on the resistance element 4, and having a leaf 25 extending radially inwards from the point 26 on the ring diametrically opposite to the projection 5, and provided with a central pivot hole. The rotor contact is rotatably mounted by means of a rivet 27, the radial leaf 25 being pressed against the underside of the rivet head 35 by a spring washer. The plane of the ring portion 24 of the rotor contact is inclined to that of the radial leaf 25 so that the projection 5 bears with spring pressure on the resistance element 4. This is secured at its ends on the inside face of the part 3 of the casing by rivets 33, the outside heads of which and of the central rivet 27 are clamped on terminals 6, 8. The head 35 of the rivet 27 is rounded and fits with clearance in a corresponding recess in the actuating member 9. The radial leaf 25 of the rotor contact engages at 10 in a corresponding radial slot 37 in the actuating member 9. The head of the member 9 is otherwise snugly accommodated within the ring portion 24 of the rotor contact without touching it, so that it does not interfere with the springing of this ring portion.