Patent GB-281252-A (GB)
IPC: B23G1/32
Filed: 1927-11-07
Abstract: 281,252. Mirfield, G. E. Nov. 29, 1926, [Convention date]. Milling screws; chucks.-In a thread-milling machine, particularly for milling tapered or parallel threads on pipe-ends, the work extends through a hollow rotatable container which carries workgripping means and is rotated and fed axially to carry the work past a threading cutter having annular teeth without lead. A preliminary turning operation on the end of the pipe is performed by a roughing-cutter acting in conjunction with the threading-cutter in a manner similar to that described in Specification 227,465. The base 1 carries a vertical pillar 2 on which are mounted heads 4, 5 carrying respectively the spindle 8 of the roughing cutter R and the spindle 9 of the threading cutter T. The vertical adjustment of the heads is effected by screws 6, 7 respectively. The tool spindles are driven from a main shaft 15 through bevel gearing 13, vertical shaft 12 and worm gearing. An upper portion 20 of the base 1 carries a member 22 which is secured in position by bolts 23 engaging transverse slots in the part 20, and is adjusted by a screw 30 actuating a block 28. The base 22 has arcuate slots to take the bolts 23 and is angularly adjusted on a pin 29 secured to the block 28. The work support 35 is provided with bearings for a rotary hollow spindle 41 through which the pipe P extends and which carries at its forward end a part-spherical centring-ring 44, the ring being driven with the spindle 41 by means of a stud 46. The front of the ring is threaded to receive a chuck plate 49 having grooves fitted with radial jaws 50 which are closed to grip the work by means of a cam ring 51 coacting with pins 53 secured to the chuck jaws. The interior of the pipe is supported near its end by means of blades 54 which are expanded into contact with the bore of the pipe. A suitable bearing is provided for the outer end of the pipe. The spindle 41 carries a worm wheel 60 driven by a worm 61 on a cross shaft 62, the worm 61 having clutch teeth 64 engageable by a sliding clutch member 65 on a sleeve 66 loose on the shaft 62. The sleeve itself carries a fixed worm wheel 69 and a loose clutch member 67 integral with a gear 68. The wheel 69 is driven from the main shaft through worm gearing 75, universal shaft 72 and shaft 71. A lever 40 controls the clutch member 65, the clutch in one position driving the worm 61 to rotate the spindle and in the other position the wheel 68. In order to impart the desired longitudinal movement to the work during operation, ring 80 on the work spindle carries a screw of preferably about ten times the pitch of the thread to be formed, the screw co-acting with a nut member 82 which is driven at a slightly lower speed than the screw to give the necessary forward feed. The periphery of the nut is formed as a worm wheel and is driven by a worm 83 on a. shaft 84 driven from the shaft 62 by change gearing. An overrunning clutch member is embodied in this gearing. In order to return the work spindle after the threading operation the nut 82 is driven at high speed from the gear 68 which drives a gear 98 on the shaft 84, the rotation of the shaft 62 and of the work swindle are suspended during this operation. The movements of the clutch member 65 are effected automatically. For this purpose a groove 102, Fig. 10, in the spindle is connected by a roller 103 to an arm 104 which, during the movement of the work-spindle actuates a. slide 108 which carries a stop 112 and a slotted link 113. The stop co-acts with a latch engaging a pin 115 on the clutch operating lever 40. To start the operation, the lever 40 is moved manually to engage the clutch to rotate the shaft 62 and in this position the lever is secured by the latch 114. On completion of the thread the stop 112 trips the latch, whereupon the lever is thrown over by a spring to initiate the return movement of the work-spindle. At the end of the return movement the end of the slot in the link 113 engages a pin 117 on the clutch lever to move the latter to a neutral position and stop the machine. The roughing-cutter R arranged in front of the threading-cutter is first brought into operation and the threading-cutter is subsequently fed in tangentially to depth and both cutters then continue to operate until, after about one and a quarter revolutions of the work, the thread is completely formed. The feed of the roughing and threading heads is controlled from the shaft 84 which is arranged to drive, through a telescopic shaft 136 and further gearing, a disc 143 provided with pairs of adjustable contacts 144, 145. The feed screws 6, 7 are respectively driven through gearing from electric motors 162, 173 mounted on brackets on the pillar 2, the starting of the motors at the proper times in the cycle being effected by the contacts 144, 145, which coact with spring contact fingers 178, 179 and act in conjunction with overload reversing switches S, S<1> in the motor circuits. These switches are so arranged that when overload is thrown on the corresponding motor the switch breaks the circuit and is automatically moved so that when the circuit through the switch is re-established by one of the contacts 144, 145, the motor is operated in the reverse direction. The movements of the head 4 are positively limited by a pair of stops 185, 186 and those of the head 5 by stops 187, 188, the engagement of a head with its stop causing overloading of the motor and disengagement of the switch S or S'. A master switch M may be located between the switches and the power line. The cutters are arranged to move, from the dotted to the full line positions shown in Fig. 12. A stop 190 serves to determine the position of the pipe as it is pushed into the work spindle and the angular position of the work support on the pin 29 is set according to the taper of the thread to be formed so that during the longitudinal movement of the work relatively to the cutter a radial movement is also imparted to give the required taper.