Patent GB-343834-A (GB)
IPC: B23G1/22
Filed: 1930-05-05
Abstract: 343,834. Tapping. VEREINIGTE STAHLWERKE AKT.-GES., 67, Breitestrasse, Dusseldorf, Germany. May 5, 1930, No. 13820. Convention date, May 4, 1929. [Class 83 (iii).] Taps.-In apparatus for cutting taper internal screw-threads in pipe fittings, flanges, sockets, &c. an expanding tap is used comprising dies 4 slidable in radial slots in a head 2 and having grooved ends engaging a slotted tapered guide 5 removably secured at 7 to a mandrel 6. The mandrel is slidable in the driving sleeve 1 of the head and is given a differential feed relatively thereto for producing the taper. The sleeve 1 is fed axially during tapping by a lead screw 9 keyed thereto and a fixed nut 10. A second lead screw 11, of different pitch from the screw 9, is secured to the mandrel by a bolt 13 which passes through a slot 12 in the driving sleeve so as to cause the screw to be rotated with the sleeve but to allow relative axial movement. A nut 15 engaging the screw 11 is held stationary in a bracket 14, the difference in pitch between the sleeves 9, 11 causing the mandrel 6 to impart the necessary taper to the work. For tapping reversed tapers, as in pipe couplings, two screws 11 may be provided having pitches respectively greater and less than that of the screw 9, the mandrel being adapted to be coupled to either screw alternatively. The pitches of the screws may be arranged to give equal or different tapers in the two parts of the work. The bracket 14 is mounted on a fixed pin 16 and is prevented from moving axially by a shoulder 17 on the pin and a lug 19<1> on the boss of a lever 19, rotatable on the pin, engaging with a stud 18. The lever 19 rests on a cone 20 adjustably secured to the driving sleeve 1, the action being such that when the desired length of thread has been cut the lever is rocked into a position where the lug 19<1> releases the stud 18 and allows a spring 21, secured at 22 to the sleeve, to withdraw the bracket 14 and the mandrel 6, thus collapsing the tap. The sleeve 1 is rotated by the usual reversing drive and on withdrawal of the sleeve a lever mechanism returns the bracket 14 into position against the shoulder 17 and the lever 19 then drops behind the stud 18 by gravity. Adjustment of the depth of cut is effected by rotation of the nut 15 in the bracket 14 through a worm drive 24, both nuts being capable of this adjustment when double tapers are being cut. In a modification the screw 11 is replaced by a plain sleeve secured to the mandrel 6 and provided with an annular groove which engages a roller adjustable along a slotted lever pivoted to the bracket 14. The free end of the lever is provided with a toothed sector meshing with a toothed sleeve slidable along a guide bar secured to the machine frame parallel to the axis of the sleeve 1. A flange attached to the cone 20 engages the toothed sleeve and moves it forward during tapping, thus rocking the lever and traversing the mandrel at a rate different from that of the sleeve 1, this rate being adjustable by moving the roller along the slot in the lever. On completion of the tapping operation, the lever 19 releases the bracket 14 and allows the spring 21 to withdraw the bracket and the pivot of the slotted lever, thus collapsing the tap.