Patent GB-899155-A (GB)
Title: Automatic cutter grinder
IPC: B24B3/02
Filed: 1961-03-14
Abstract: 899,155. Grinding cutting tools. CINCINNATI MILLING MACHINE CO. March 14, 1961 [March 14, 1960], No. 9257/61. Class 60. A machine for automatically grinding the teeth of a helical stagger or plain tooth cutter 20 comprises a table 12, Fig. 1, mounted for movement relatively to a grinding wheel 28, a rotatable head 15 on the table for supporting the cutter, means for intermittently indexing the head 15 to bring successive teeth into grinding position, means for providing a signal at the end of each complete revolution of the cutter and transmitting it to a counter which after a predetermined number of revolutions of the cutter transfers the signals to a second counter. The two counters are pre-settable to the number of revolutions of the cutter for the rough and finish grinding operations respectively, and are arranged to control these operations. A third counter, which registers a count at the end of each indexing movement of the cutter, is arranged at the end of each complete revolution of the cutter to register a count in the first counter and, when the latter counter counts out at the end of the prescribed number of rough grind revolutions for which it is set, transfers its registrations to the second counter which similarly counts out at the end of the prescribed number of finish grind operations for which it is set. The cutter 20 is disposed on an arbor 19 mounted between the head 15 and tailstock 16 on the table 12 which is slidable axially of the cutter on a transversely-adjustable saddle 11. The table 12 is moved on the saddle to cause each cutter tooth to traverse the cup-shaped grinding wheel 28 by a motor M6 operating through rack-and-pinion gearing which is disconnectable by energizing a solenoid 3 SOL to permit manual positioning of the table. At the end of its travel, adjustable stops 36, 36<SP>1</SP> on the table actuate a limit switch 1LS which through suitable time delay and other relays successively de-energizes the motor, brakes it dynamically, re-energizes it and shorts out its starting resistance. Predetermined feed movements are applied to the saddle 11 by corresponding rotation of a feed screw 39, Figs. 2 and 4, engaging a nut 42 fixed to the bed, the screw carrying for this purpose a ratchet wheel 61 for actuation by a pawl-carrying arm 62 through linkage 71 and eccentric pin connection 69 with a cam 68 driven from a motor M4; a limit switch 3 LS opens the circuit of the motor after each complete revolution of the cam. The extent to which the arm 62 is swung upon each revolution of the cam and therefore the corresponding feed of the saddle is determined by the coaction of a pitman 95, which fits over a pin 64 on the arm and is carried by swinging arms 101, 102, with either of two cams 80, 81 or a stop 82, all mounted on a shaft 83. By appropriate energization of solenoids 1 SOL, 2 SOL in the automatic cycle of the markers the pitman can be positioned so that it coacts with the cam 80 for rough grind feed, cam 81 for finish grind feed and stop 82 for feed to compensate for trueing of the grinding wheel; the cams and stop are each manually adjustable relative to the axis of the shaft 83 to set the precise feed in each case. As each tooth of the cutter is traversed across the grinding wheel by movement of the table 12 a torque motor M5, Fig 1, which rotates the head 15 through a belt drive 18 is arranged to exert torque to hold the tooth being operated upon against a fixed tooth rest 220, Fig. 11, on the wheel head 29. At the end of the left-hand traverse, Fig. 1, in the case of helical tooth cutters, the tooth being operated upon leaves this tooth rest and passes on to an index control rest 222, and the actuation of the table limit switch 1LS results in the motor M5 being energized in reverse to bring the next tooth into position, the passage of the cutter across the rest 222 operating a switch 4LS to cause feed torque to be applied to the motor to urge the next tooth against the rest 220. While for helical tooth cutters indexing occurs only at the end of the left-hand traverse for stagger tooth cutters indexing occurs at both ends of the traverse, an index control rest then being provided to move with the table. A switch in the circuit can be set to provide not only for indexing in accordance with the type of cutter being operated upon, but also to arrange for the motor M5 to be energized through different variable transformers in the different directions of traverse when dealing with right-hand and left-hand helical cutters and so permit the greater torque necessary to hold the tooth against the tooth rest in one direction of traverse than in the other to be provided by suitable setting of the transformers; when the switch is set for stagger tooth cutters, the same torque is applied in both directions of traverse. To achieve perfect roundness of the cutter it is desirable to arrange, preferably only during the rough grind operation, for indexing of the cutter through 180 degrees after each complete revolution of the cutter. The trueing diamond 127, Fig. 8, is carried by a bar 126 which is vertically reciprocated in a ball-way housing 129 in a slide 130 guided for reciprocation on a saddle 122 which is clamped on the wheel head 29 and can be pivoted through 90 degrees should it be desired to true the wheel periphery. Reciprocation of the bar 126 for a normal trueing operation is effected by a motor M3 which is automatically brought into action after a predetermined number of revolutions of the cutter. The motor, which is controlled by a switch 2LS, is carried by the slide 130 for driving through gearing 159 a shaft 162 carrying an eccentric plate 163 having a circular groove 164 engaged by a roll 165 on the bar. At the end of each reciprocation of the bar, the slide 130 is fed towards the grinding wheel by a lead screw 132 engaging a nut 133 in the saddle 122, either of two feed pawls 170, 171, according to the desired direction of feed, engaging respective ratchet wheels 136, 137 on the lead screw. The pawls 170, 171 are carried by respective arms 174, 175 which are so controlled by cams 182, 183 driven with the gear 159 that near the end of the upstroke of the bar 126 whichever of the pawls is not then masked by members 200, 201 on a hand-operated slide 199 is moved to rotate the screw and advance the slide a predetermined amount towards the grinding wheel. The various motors and solenoids are arranged for control in a control circuit which includes the limit switches, time delay and other relays, and eight counters determining and controlling certain aspects of the cycle. Each counter, which comprises a clutch coil arranged to be energized to enable it to operate and to be reset when the coil is deenergized and a count coil arranged to enter a count each time it is deenergized, is pre-settable to control, at the point where it counts out, a desired step in the cycle. Of the eight counters in the circuit, counter 1 is set to the number of rough grind operations on each tooth, counter 2 to the number of finish grind operations on each tooth, counter 3 to the number of teeth on the cutter, i.e. the number of indexing movements for a complete revolution, counter 4 to half the number of teeth on the cutter, counters 5 and 6 to the number of teeth to be ground respectively for each rough and finish grind feed of the saddle and corresponds normally to one revolution of the cutter, counter 7 to the number of teeth to be trued at each trueing operation, again corresponding to one or more revolutions of the cutter, and counter 8 to the number of trueing passes for the trueing operation. The cycle consists, in the case of a helical toothed cutter, of successive traverses of the cutter from right to left and back with the cutter held by the motor M5 against the tooth rest so that the teeth are successively traversed across the grinding wheel, the cutter being indexed from one tooth to the next when in the left-hand position and each indexing movement being registered by the counter 3. In the first rough grind part of the cycle the cutter is given as many revolutions (and therefore each tooth is given as many operative traverses) as are prescribed by the counter 1, a count bÚing made in this counter each time the counter 3 records one revolution of the cutter until, when it finally counts out, the second finish grind part of the cycle is initiated; the counter 3 then registers each revolution of the cutter in the counter 2 which counts out after the prescribed number of finish grind operations for which it is set. With the counter 4suitably set the circuit provides for automatic indexing of the cutter through 180 degrees after each rough grind revolution, movement of the table being prevented during this operation and the counter being advanced one step for each indexing movement so that it counts out after the cutter has rotated through 180 degrees. The intermittent feed of the cutter during rough grinding operation occurs after each index of the number of teeth to which the counter 5 is set, the counters 3 and 5 counting out at this stage and resulting in the saddle motor M5 being energized and the cam 80 rendered effective to cause feed to the extent set by the cam. At the end of the rough grind, the cutter is inwardly fed for the first finish grind by the motor M5, with the cam 81 effective and thereafter intermittently by the same means under the control of the counter 6. Trueing of the grinding wheel is carried out at the regular intervals set by the counter 7, e.g. after every two revolutions of the cutter, the counter counting out at these times to energize the trueing motor M3 to effect as many trueing passes as are set by the counter 8; at the end of each trueing pass the saddle motor M5 is energized for a further feed of the cutter to compensate for the amount of material trued from the grinding wheel, the stop 81 then being effective to determine the extent of feed. When the