Patent GB-312895-A (GB)
Title: Improvements in machines for milling threads
IPC: B23G1/32
Filed: 1928-11-20
Abstract: 312,895. Mirfield, G. E. Nov. 20, 1928. Milling screws.-A machine for milling screw threads, particularly taper threads on the ends of pipes, comprises a roughing-cutter and a threading-cutter which are independently driven and are mounted on separate slides moved to and from the work in timed relation with the rotary and longitudinal movements of the work. The operation is similar to that described in Specifications 227,465 and 281,252. The base 1 carries a pedestal 2 provided with slideways 3 on which are mounted a slide 4 carrying a roughing-cutter R on a spindle 7 and an oppositely-disposed slide 5 carrying a threading-cutter T on a spindle 20. The cutter R is mounted as shown in Fig. 18, the cutter being secured to an extension 9 which is integral with a face-plate 10 secured to the front of the spindle and which carries a plug 10<1> seating in a bore 11 in the spindle end. The roughing-cutter is driven from an electric motor RM through a flexible coupling 15, shaft 16, and worm gearing 18, while the threading-cutter is similarly driven from a motor TM through a coupling 21, shaft 22, and worm gearing 25. The head 4 is provided with a depending lug 30, Fig. 17, in which slides a non-rotary screw 32 coacting with a nut 31 which is rotated to effect longitudinal adjustment of the screw by wormgearing 40 actuated from a crank 42. A scale 46 is provided to indicate the setting of the worm shaft 39. The end 33 of the screw 32 coacts with a fixed stop 43 and thus serves to limit adjustably the movement of the roughing cutter-head towards the work. These movements are effected by a fluid-pressure cylinder 50 whose piston is con nected to the screw 32, and which is supplied with fluid from a pump OG driven by a chain C from a motor OGW. This motor also drives through a chain C<1> a pump OG<1> supplying fluid to a cylinder 61 which actuates the threading cutter-slide 5. The inward movement of this slide is limited in a similar way to that above described by means of a screw 55 which is moved longitudinally by means of a nut 56 which is rotated by worm gearing 59 and crank 60. In place of the fixed abutment 43, a cam 65 engaged by a roller 64 on the screw 65 is provided to limit the movement of the threading-cutter towards thework. The work P, such as a pipe to be threaded, is suitably supported at its outer end, and is pushed into a hollow container 70, Fig. 4, against a fixed stop 91. The container is adjustable by means of a screw 75, and is journaled in a housing 72' fitted with a removable cap 80. The container is rotated by means of a splined wormwheel 100 driven by a shaft 102 which carries an integral clutch member 105 coacting with one side of a double clutch member 106 slidably keyed on a sleeve 107 which is rotatable on the shaft 102 and to which is keyed a worm wheel 110 which is driven through a worm 111, shaft 112, vertical shaft 115 and further gearing from a motor DR. The sleeve 107 also carries a loose gear 108 coacting with the double clutch member. The double clutch-member is actuated by means of a fork 120 secured to a shaft 121 which is moved longitudinally by a spring-pressed plunger 124. The threading-cutter is provided with annular rings of teeth without lead and the work is moved longitudinally per revolution by a. distance equal to the pitch. This is effected by means of a master screw 130 preferably of, say, ten times the pitch of thread required, this screw coacting with a nut 131 driven at nine-tenths of the speed of the screw. 'The screw rotates as' a unit with the container and the nut is driven at the required speed by means of a worm 133 mounted on a shaft 134. The latter shaft is driven from the shaft 102 through two-speed gearing 135 - - 137 so that threads of different pitches. may be cut without changing the master screw. The loose gears 139, 139<1> may be coupled to the shaft 139 through an overrunning splined clutch 140. In order to return the container to the starting point on completion of the thread, the wheel 108 is connected to a wheel 148 keyed on the shaft 134, so that when the double clutch 106 is engaged with the gear 108 the rotation of the sleeve 107 is transmitted to the shaft 134 which is then rotated at high speed while the clutch 140 overruns the gear 139. The nut is thus rotated while the rotation of the container is arrested owing to the disengagement of the double clutch from the member 105. This causes a quick-return longitudinal movement of the container. The movements of the double, clutch at the required times in the cycle are effected automatically. For this purpose, a pivoted latch lever 151 has a projection 151<1> which is spring urged to engage a lug 152 on the shaft 121 and hold the clutch in the position shown in Fig. 14. A shaft 161 carries a forked finger 163 extending over the shaft 121. The shaft 134 drives a wormwheel 168 mounted on a bushing 162 and connected through a train of gearing 169 - - 174 with a timing-disc 177, Fig. 20, which makes one revolution for each complete threading cycle. The shaft 102 is similarly arranged to drive a wormwheel 166 carrying pins 181, 182, which coact with a loose, dog 180 which at the required time trips the latch 151 and allows the shaft 121 to be moved by a spring 156 to cause the return movement of the container. At the end of the return movement the clutch is moved to a neutral position by means of the fork 163 on the shaft 161 which is actuated from a cam 190, Fig. 11, connected to the gear 168. Since the threading cutter is of taper form, the cutter is fed radially into the work to compensate for the relative longitudinal movement. This is effected through the cam 65 forming the abutment of the screw 55 The cam is moved through a link 210 connected by a block 212 to the groove 90 in the ring carried by the container. Thus as, during the threading operation, the container moves longitudinally, the cam 65 is rotated to cause the threading cutter slide to be moved progressively towards the work. The timing-disc is provided with spaced ridges carrying dogs controlling the movements of the roughing and threading slides. The dogs coact with rollers mounted on levers 228 and 230 which are pivoted at fixed points' 229 and 231 respectively. The lower end of the lever 228 is connected by a link 240 and lever 241 to a rod 242 controlling the reversing-valve of the cylinder 50, the movements of lever being such that the valve is succesively moved to forward, reverse, and neutral positions. The lever 230 is similarly connected to the controlling valve of the cylinder 61. The motor OGM is arranged to drive a lubricating-oil pump OP from which oil is directed to the cutters and other parts. In operation, the double clutch 106 is first manually operated to initiate the work rotation and the roughing-cutter is moved up to the work, Fig. 24a. After rather more than half a revolution the threading-cutter is moved up to operate on the surface exposed by the roughing-cutter. On completion of a revolution the roughing-cutter is withdrawn while the threading-cutter continues to operate, and the thread is completed after the work has completed rather more than a revolutionin contact with the threading-cutter. During the threading, the cutter is gradually fed in to compensate for the changing radius of the work due to the taper thread. On completion of the thread, the slide 5 is withdrawn and the latch 151 is then tripped to initiate the container return. At the end of the return movement the double clutch is automatically moved by the finger 163 to a neutral position to stop the container whereupon the work is removed. For cutting parallel threads the link 210 is disconnected so that the cam 65 acts as a fixed abutment for the threading-cutter slide. Chucks.-The pipe is secured in its container by a chuck comprising jaws 82 supported in an annular plate 83 screwed into a bushing 84 seated in the container. The jaws are operated by a cam-ring 85 coacting with rollers 86 secured to the jaws. A ring 88 is secured to the plate 83 and is cut away so as to allow manipulation of the cam-ring.