346,743. Grinding. JACKSON, L. MELLERSH-, 28, Southampton Buildings, London.-(Jones & Lamson Machine Co. ; Springfield, Vermont, U.S.A.) Oct. 14, 1929, No. 31185. [Class 60.] Screw-threads, grinding; milling-cutters and like tools, sharpening; trueing rotating tools.-A machine for grinding the threads on taps is provided with means for grinding the relief on the threads, and means are provided for trueing the grinding-wheel; the machine also may be employed for grinding reamers, hobs, &c. The machine consists of a base 1 having mounted thereon, on slideways 2, a carriage 3, which is traversed by means of a cam 6 mounted on a drum 7 and engaging a roller 5 journalled in a bracket 4 depending from the carriage, a spring 10 giving the return movement of the carriage. On the carriage are mounted head- and tail-stocks, the head-stock consisting of a sleeve 20 adjustable in a bearing 21 by a pinion 22 and rack teeth 23 on the sleeve, and slidably carrying a centre 30 pressed outwardly by a spring 32 to an extent allowed by the engagement of a gear segment 35 with rack teeth 34. The sleeve 20 carries a face-plate 40 with a work driving arm 41 and is driven by a pinion 43 carried by a shaft 44, driven, through gearing 47, 48 from a shaft 49 mounted in the carriage. The tail-stock comprises an adjustable sleeve 60 similar to the sleeve 20 and carries a centre 70 to which a pivotal movement is given to produce a movement of the tap for grinding the relief. The centre 70 has secured thereon a spherical block 72 seating in a mating socket 73 carried by the sleeve 60 and the shank of the centre extends through a sleeve 76 rotatable in the sleeve 60 and carries a spherically surfaced collar 88 located in an opening 87 in a block 80. The block is adjustable transversely of a gear 77 carried by the sleeve 76 so that the end of the shank of the centre 70 is carried round in a circle of adjustable diameter ; locking screws and an adjusting nut 94 are provided. The pivotal movement is timed to the rotation of the tap by gearing 103, 104 from the shaft 49. A modified mechanism for giving the relieving movement to the tap comprises pivoting the centre transversely of its axis in the sleeve 60 and rocking its outer end by a crank mechanism; relieving movement also may be given to the centre 30. The grinding-wheel 155 is carried by a shaft mounted in a plate having a circular extension 153 journalled, and angularly adjustable according to the pitch angle of the thread of the tap, within a casing 154 formed on a carriage 160 slidable to and from the work on the base 1. The wheel is driven through a belt 167, by an electric motor 165 pivotally mounted coaxially with the part 153 on a cradle 162 on the carriage 160. In order to avoid reversal of the rotation of the tap during the reverse movement of traverse, the grinding-wheel is withdrawn during that movement, the feed and withdrawal movements of the wheel being brought about by a lever 196 which engages a cam member 195 on the drum 7, and also engages a notch 198 in an internally screwed sleeve 182 engaged by a screw 187 carried by the carriage 160 ; a spring 200 serves to draw the wheel into cutting position, the forward motion being limited by a stop 202. The position of the slide 160 relatively to the plunger may be altered by rotation of the screw 187, through gears 205, 206 by a shaft 207, rotatable by a hand-wheel 209 or by a power feed mechanism. This is actuated by a cam member 220 on the drum 7 and consists of an arm 222 on a shaft 223 carrying a lever 224, which moves, through a link 225, a pawl 235 engaging a ratchet wheel 237 geared to the shaft 207, the feed at each movement being determined by an adjustable stop 240 ; the total feed also is limited by an adjustable arm 250 having a cam portion 251 which moves beneath the pawl 235 and lifts it clear of the ratchet teeth. Trueing means are provided for trueing the grinding- wheel, comprising a slide 270 mounted on the slide 160 and movable thereon by a screw 271 rotatable by a hand-wheel 279. A sleeve 276 is mounted on the screw and carries a gear 277 engaging a gear 190 on the screw 187 so that, when the hand-wheel 279 is clamped by a nut 280 to the sleeve 276, the screws 187, 271 rotate and the slides 270, 160 are fed at the same rate. The slide 270 has mounted thereon three shafts 294, 299, Fig. 9, carrying offset diamond &c. tools 301 to operate on the periphery and inclined side faces of the wheel, and the shafts are geared together by gearing 295, 297, 298, being oscillated by a link 324 connected to an arm 320, Fig. 2, on a shaft 315 carrying an arm 312 engaging a cam element on the drum 7; a spring 318 normally holds an arm 316 on the shaft 315 at an inner limit determined by a screw 317. In a modification, the shafts carrying the diamond tools carry gear segments engaging a segmental rack bar moved by the segment on one of the shafts. The carriages &c. are driven by a main shaft 353 driven by a belt from an electric motor 350, the shaft acting through spur gearing to drive the shaft 49, a clutch, operated bv a handle 367 being interposed, and acting, through worm gearing 379, 380, to drive the drum 7. In operation, a working traverse of the tap is made and the threads are ground to shape and with the relief. On the return stroke, which may be made at a higher speed, the grinding- wheel is retracted from the thread and the trueing devices may be actuated to trim the wheel, this cycle of operations being repeated until the tap is to size, the feed being set so that prior to the lifting of the pawl the grinding-wheel is trued and the finishing cuts made with the trued wheel; the pawl lifting gear is set back on the completion of each work piece to allow for the reduction of size of the wheel. In a modification, the cam 6 has portions arranged to give two traverses for each rotation of the cam, and the trueing mechanism is arranged to give a single oscillation after the first traverse and a reverse movement during the next traverse.