Patent GB-1203352-A (GB)
Title: Method of and apparatus for tapping holes
IPC: B23G1/16
Filed: 1968-08-29
Abstract: 1,203,352. Tapping. HERBERT LINDNER G.m.b.H. 29 Aug., 1968 [15 Sept., 1967], No. 41385/68. Heading B3N. In a method of tapping a blind hole to a predetermined depth, the tapping spindle 2 of a machine 1 is fed axially at a rate which is greater or less than the intrinsic axial feed rate of the tap 7 dictated by its speed of revolution and pitch but is in fixed proportion thereto, the tap holder 6 allows axial displacement of the tap 7 relative to the spindle 2 to accommodate the difference between the movement of the spindle 2 and the actual penetration of the tap 7, and the instant at which the tapping operation is interrupted is determined by reference to the movement of the spindle 2 which will then be in fixed proportion to the actual penetration of the tap. The spindle 2 is driven by a synchronous electric motor 14 through electromagnetic reversing clutches 17, change-speed gearing 12, a drive pulley 13, V- belts 11, and a driven pulley 18 slidably keyed to the spindle. A second synchronous motor 24 fed from the same power source as the motor 14 is connected through V-belts 27, worm gearing 28, 29, electro-magnetic reversing clutches 23, and change-speed gearing 20 to a pinion 19 meshing with a rack 18 which is either secured to a sleeve 3 carrying the spindle 2 as shown so that the sleeve is fed through a spindle head 4, or in a modification, Fig. 2 (not shown), is secured to the head 4 so as to feed the head 23, and change-speed gearing 20 to a pinion 19 meshing with a rack 18 which is either secured to a sleeve 3 carrying the spindle 2 as shown so that the sleeve is fed through a spindle head 4, or in a modification, Fig. 2 (not shown), is secured to the head 4 so as to feed the head together with the sleeve and spindle A second rack 31 meshes with a pinion 32 on a counting device 33 which transmits signals representing the axial movement of the spindle 2 to a control cabinet 35 where the signals are compared with programmed values fed in by punched tape 36. Output signals from the cabinet 35 are transmitted to an amplifier 38 having output wires 39, 40 connected to the clutches 17, 23. The tap holder 6 includes a sleeve 48 which carries the tap 7 and is slidably mounted on a shaft portion 42 having a tapered shank 41. A ball 45 located in a groove 44 and in a slot 46 in a bush 47 secured in the sleeve 48 couples the sleeve and shaft portion for conjoint rotation. A compression spring 49 is either arranged between the bush 47 and a collar 43 as shown to urge the sleeve 48 into a retracted position on the shaft portion 42, or in another arrangement, Fig. 5 (not shown), the spring urges the sleeve into an extended position. In operation, the spindle is rotated at the tapping speed and advanced rapidly until the tap 7 is in close proximity to the workpiece. The spindle 2 is then fed at the predetermined axial feed rate, the difference between the spindle feed movement and the actual penetration of the tap into the hole being accommodated by compression of the spring 49, and when the extent of spindle movement signalled by the counting device 33 coincides with the programmed value, the direction of rotation and feed is reversed. When the tap 7 leaves the hole the spindle 2 is returned rapidly to the initial position.