Patent GB-432504-A (GB)
Title: Improvements relating to the abrading of hard material
IPC: B24C1/00
Filed: 1934-01-29
Abstract: 432,504. Grinding hard material; chucks. ANGELL, R. C., Prince Bay, New York, U.S.A. Jan. 29, 1934, No. 2964. [Class 60] [See also Group XXII] Hard material, such as hardened steel, is ground by propelling abrasive-carrying liquid into contact conjointly with the surface to be ground and a surface of a material harder than the material to be ground. The abrasive-containing liquid may be projected at high velocity against the surface to be abraded by the action of a rotating wheel harder than the material to be ground, and in immediate proximity to the work, the liquid being fed into the space between the work and wheel. An abrasive wheel may be employed having the hardest vitrified bond commercially available, glazing of the wheel not occurring owing to the fact that the abrasive action is performed by the particles in the liquid carried round by the wheel and temporarily adhering to it, rather than by the abrasive in the wheel. The abrasive in the liquid is preferably less hard than that in the wheel. Owing to the low temperatures and small forces occurring during the process of grinding delicate articles may be formed from pre-hardened steel, without softening or distortion. The process is described as applied to two machines, one for forming the heads on hardened blanks for dental burrs, and the other for cutting the teeth on them. In the first of these machines, shown in Figs. 2, 3, 5, 9, 10 and 21, cylindrical blanks B are automatically fed from a magazine 24 to a chuck 20 in which they are held between backing wheels 70, 71 shaped, as shown in Fig. 10, to produce a shoulder on the blank. The bearings of these wheels are mounted on slides 76, 77, Fig. 3, which during the cut are moved, at first rapidly and then slowly, towards one another by segmental gears 78, 79 meshing with rack-bars 82, 83 in the slides and operated at the appropriate times by roller arms 84, 85 actuated by cams 90, 91. Springs 92, 93 tend to move the slides outwardly, and so keep the roller arms in contact with the cams. The depth of cut may be varied by adjusting the rack bars 82, 83, relatively to the slides 76, 77 by the rotation of sleeves 96, 97, which are screwed into the ends of the slides and are traversed by headed rods 98, 99 extending from the rack-bars. The backing-wheels 70, 71 are composed of particles of abrasive, such as alundum, in a vitrified bond so hard as to be unsuitable for cutting purposes; and abrasive-containing fluid, preferably a mixture of sperm oil and fine emery, is supplied to the tapering space between them from a downturned nozzle 110. As shown in Fig. 9, the tapered end of the nozzle is of rectangular form, and it is divided by a partition 126 which extends beyond its end and is cut away on each side at 127, 128 to conform to the shape of the peripheries of the wheels 70, 71 between which it extends. Two separate streams of the fluid are thus directed between the peripheries of the backing wheels and the opposite sides of the blank. The abrasive fluid and the discharged blanks pass down a conduit 118, in the inclined portion of which is a perforated plate 122 which allows the fluid to pass to a trough 121 and thence to a reservoir 112 for re-circulation, whilst causing the blanks to fall into a tray 123. The means for feeding the blanks, Fig. 5, comprises a carriage 33 slidable on a horizontal bar having a groove in the upper surface in which rests the lowermost blank of the vertical pile in the magazine 24. The carriage when moved forward pushes the blank into the end of the axial bore 23 of the chuck mechanism. The movement of the carriage is produced by a cam 45 operating a roller arm 43 pivoted at 44, which reciprocates a head 41 through an adjustable pivotal connection 48 which allows the stroke of the head to be varied. A lateral finger 40 on the head 41 moves a rod 35 which passes through the carriage 33 and carries a spring 36 bearing on the end of the carriage, which is thus moved forward under pressure of the spring. The bore 23 of the chuck mechanism contains a line of the blanks, so that the insertion of a new blank ejects the completed blank and pushes the next blank into operative position, a stop 60, Fig. 2, being temporarily moved forward by mechanism including a cam 67, gear 63, and rack 62 to abut against the end of the new blank to position it. The chuck mechanism comprises a split chuck 20 having a coned outer surface engaged by a similar surface on a sleeve 19 pressed forwardly by the rod 22 to close the chuck. The work is released by a cam-actuated lever 54, which moves a collar 53 slidable on the hollow spindle 15 and operates levers 52 pivoted in slots in the spindle and bearing on the end of the rod 22. This releases the rod 22 and allows a spring 51 in compression between the inner end of the chuck 20 and a shoulder on the sleeve 19 to retract the latter and allow the chuck to open. To prevent entry of the grinding fluid into the chuck, oil or other fluid is supplied by passages 133, 134 into the bore of the spindle 15 and flows out through the chuck. The blanks formed in the above-described machine are toothed in the machine shown in Figs. 12-16. This comprises an inclined bed carrying transverse brackets 212, 213 in which are formed guide ways 214, 215, Fig. 15, for the side bars 216, 217 of a rectangular frame forming the work-supporting carriage. The upper sides of the guide ways are formed by rollers 221, 222. The carriage is reciprocated by a cam 226, against which a roller 225 on the lower end of the carriage is caused to bear by gravity. The roller 225 is adjustably mounted to enable the stroke of the carriage to be varied. The workcarrying head comprises an apertured member 232, Fig. 14, bridging the carriage and having a yoke 236 pivoted thereto, to which in turn is pivoted a cradle 240 in which a chuck sleeve 242, for the work B<1> is rotatably mounted. To alter the depth of cut, the yoke 236 is adjusted angularly about its pivots and secured by set-screws 237, 238, Fig. 13, thus moving the work to or from the backing- wheel 245. During reciprocation of the carriage, a cam 247 engaging an arm 248 secured to the cradle 240 rocks the cradle to move the blank towards and from the backing-wheel. The work is supported by a notched rest-plate at the forward end of the cradle 240, and is indexed by rotating the chuck sleeve 242 by hand to extents determined by the engagement of a spring-mounted pin with a notched wheel 269 on the chuck sleeve. The shaft of the backing wheel 245 is mounted in a bearing 256, carried on a plate 257 pivoted at 258 so that it may be raised and lowered by a screw 260 to adjust the wheel vertically. The bearing 256, and with it the wheel, may be laterally adjusted by a screw 265. The abrasive - containing liquid is supplied, from a reservoir containing a stirrer and connected to a source of airpressure, by way of a flexible tube 305 to a header 306, from which it is directed against opposite sides of the backing wheel adjacent the work by curved nozzles 307, 308. For truing the backing-wheel, diamond tools 287, 288 are mounted in holders 285, 286 carried on a pair of longitudinal rods 283, 284, and are radially adjustable by means of nuts 289, 290. The rods 283, 284 are pivotally mounted at the ends, and at their upper ends carry gear segments 298, 299, Fig. 15, meshing respectively with toothed discs 300, 301. These discs are slotted for the passage of a bolt 303 by which they are secured in independently adjustable relation to an operating arm 304. When the wheel is to be trued, a lever 291 pivoted to the machine bed and to the end of the work-supporting carriage is depressed, moving the carriage upwardly until the diamond 287 is at the tangent point on the periphery of the wheel; the arm 304 is then rocked, thereby moving the diamond in an arc across one bevelled face of the wheel. The lever 291 is then further depressed to bring the diamond 288 to operative position to true the opposite face of the wheel.