Patent GB-241629-A (GB)
Title: Improvements in methods of and apparatus for grinding screw threads, and grooves of similar cross section
IPC: B24B19/02
Filed: 1924-07-24
Abstract: 241,629. Newman, W. H. July 24, 1924. Screw-threads, grinding. - In a machine for grinding screw-threads, or grooves not forming part of a helix but of screw-thread form in crosssection, a single grinding-wheel is employed to grind the straight flanks, the rounded root and the rounded crests of a thread. The wheel grinds the flanks and root to shape in one operation and is then withdrawn and moved to a series of positions in each of which it grinds a small portion of the crest. The screw 1 to be ground is mounted between a slidable centre 3a and a centre 3 formed on a master screw 2, the centre and the screw being supported in bearings 5 on a frame 6, which is pivoted at 7 to the machine base 8. The screw 2 runs in a nut 10, which is prevented from axial movement by the bearings 5, but may be rotated with a cam 11 secured to it. The frame 6 is pressed transversely by a spring 14 to bring the cam into contact with a roller 13; the screws 1, 2 are rotated by a pulley 15. In the first pass of the screw 1 past the grinding-wheel 9, this wheel grinds the flanks and root of the thread, the work being held in correct transverse position by the narrow end of the cam. The cam is then turned quickly to the position shown in dotted lines in Fig. 3, this movement of the cam moving the work from the grinding-wheel and at the same time, by the partial rotation of the nut 10, moving the screw axially to bring the screw and the wheel 9 to a position to grind, on the next pass of the work, a small portion of the crest of the thread. On successive strokes or passes, the cam is moved slightly, thus repositioning the work and the wheel, until the crest is completely ground. In a modification, the master, or lead screw, works in a fixed nut and moves the pivoted frame along the work. the work being driven through differential bevel gearing from the lead screw, and the planet wheels of the gearing being mounted on a frame carrying the cam, movement of which effects the resetting of the work relatively to the lead screw. Fig. 5 shows a machine for grinding parallel grooves of thread form, the work being carried on centres 3, 3<a> and driven by a wheel 24 revolving on the centre 3, and the frame 6 being moved by the lead screw 18. The wheel 24 drives a similar wheel on a spindle 26 in a sleeve 27, and the lead screw is driven through gearing 22, 28 by a wheel 29 having secured thereto a cam 31 and carried by a plate 30 attached to the frame 6; the cam 31 revolves once while the frame moves a distance equal to the pitch of the grooves. The cam is engaged by a roller 32 on a spring or weight pressed arm 33 mounted on a shaft 35 in bearings 36 on the machine base, and the arm carries an adjustablethrow eccentric 37 engaging an arm 38 forming part of the frame 6, rotation of the cam 31 thus. moving the work to and from the grinding-wheel 9; the eccentric 37 and the cam 31 are adjusted according to the depth of the thread. The cam and the lead screw are driven at variable speeds depending upon which portion of the groove is being ground, by a ratchet wheel attached to the cam and operated by a pawl actuated by a crankpin on the spindle 26, gearing operated by the crank-pin also being provided to move a guard over the ratchet wheel to the extent required to give the necessary motion to the screw and the cam. The grinding-wheel may be trued by the means described in Specification 228,445, [Class 124, Stone &c.].