GB242016A - Improvements in method of and machine for milling tapered screw threads - Google Patents

Abstract

242,016. Hall, P. P.-G. Aug. 22, 1924. Milling screws.-In a milling-machine for cut. ting internal or external taper screw-threads the cutter, which has a length substantially equal to the length of thread being cut, is given a planetary motion relatively to the stationary work, and is also moved transversely and axially relatively to the work during the cutting operation which is completed in a single planetary movement. For external threads an annular cutter 27 is secured to a spindle 16 rapidly rotated by a belt-pulley 28 and eccentrically mounted in conical bearings in a cylinder 10 eccentrically mounted in a sleeve 5 adapted to be rotated in conical bearings 3, 4. Thrust washers are provided at 12 and 18. An interchangeable screwed sleeve 29 co-operating with nut segments 30 provides for axial feed relatively to the fixed work-piece 94. The sleeve 5 is rotated by a belt-driven worm 33 and a wormwheel 34 loosely mounted on the sleeve and carrying two projections 36 engaging a radial pin 37 on the cylinder 10 projecting through an annular slot 38 in the sleeve. In operation, the cutter is first rotated while concentric with the work and the worm-wheel 34 then rotates the cylinder inside the sleeve to feed the cutter radially to the required depth into the work. The pin 37 then contacts with a screw 44 in a lug on a ring 39 clamped to the sleeve at 41 in an adjusted position as determined by a pointer 90. The cylinder and sleeve now rotate together to give the cutter its planetary movement and after approximately one revolution round the work a radial projection 51 on a ring 49 secured to the sleeve meets a lateral lug 52 on a loosely mounted ring 53, the latter being thereby rotated until a radial shoulder thereon contacts with a flange 62 on a rod 56 to withdraw the rod from a hole in a disc 60 secured to the worm-shaft 32 and thereby allow a spiral spring to rotate the disc and carry the worm, which is eccentrically mounted on the disc, out of gear with its worm-wheel. A spiral spring 47, secured at 46 and 48 to the worm-wheel and sleeve respectively, then rotates the wheel in the reverse direction and by means of the pin 37 restores the cutter to a central position, after which a weight 69 rotates the sleeve by a belt 68 and withdraws the cutter from the work. For cutting taper threads a wedge 70, Fig. 6, is introduced between the screw 44 and the pin 37 to a. varying degree to cause relative rotation between the, sleeve and cylinder during cutting. The wedge is slidably mounted in a lug 40 on the ring 39 and its rear end 74<1> is pressed against a fixed surface by a spring. The fixed surface may be the wall 75, Fig. 1, of the machine casing, or the edge 80 of a screwed ring 77, Fig. 6, slidably keyed to the sleeve and engaging a fixed nut segment 78. Alternatively the surface may be on an internally threaded ring slidably keyed to the casing and engaging a screwed ring secured to the sleeve. In the two latter modifications the rings have a thread of opposite hand to that of the feed sleeve 29 and the pitch may be greater, being preferably twice that of the feed sleeve. Specification 2797/80 is referred to.