Patent GB-483279-A (GB)
Title: Improvements in or relating to grinding or abrading machines
IPC: B24B47/20
Filed: 1936-10-12
Abstract: 483,279. Grinding internally. HEALD MACHINE CO. Oct. 12, 1936, No. 27666. Convention date, March 11. [Class 60] In an internal-grinding machine, the grinding-wheel is fed' rapidly into contact with the work, and upon contact therewith is fed more slowly, at rough grinding speed, which again is reduced for finishing ; the control of the speed upon contact with the work is brought about, irrespective of the diameter of the work, by making the wheel electrically conductive and including it in a circuit controlling the rate of feed. The machine comprises a base 6 upon which is rotatably mounted, in a work-head 2 a chuck 10 carrying the work a, and the grinding-wheel 7 is mounted in a head 3 on a bridge 4, the wheel being moved transversely to apply the feed, and the work-head 2 being mounted on a table 1 reciprocated on the base under control of dogs 16, 17 and a reversing- lever 20 actuating a reversing valve 21, which supplies fluid to a cylinder 32 containing a piston 33 connected to the table 1: The wheel-head 3 is carried by a cross slide 37 movable by a screw 38, which is geared at 41, 42, to a shaft 43 rotatable in a housing 44 either by a hand wheel 43<1> or by a ratchetwheel 45 secured to the shaft 43 and engaged by two oppositely directed pawls 46, 47, Fig. 4, carried by an annular member 48 rotatable on the shaft and moved, through rack gearing 50, 51, by a piston 62. In order to compensate for reduction in size of the grinding-wheel due to wear and dressing, the pawl 46, which causes retraction of the slide 37 after completion of grinding, is endered inoperative, for a portion of the rotation of the member 48, by means of a cam 59, which engages a pin 60 on the pawl to hold it lifted, and is movable with an arm 54 adjusted about the shaft 43 by a gear segment, 55 and a pinion 56 adjustable by a knob 58. The piston 62 moves in a cylinder 63 connected at the lefthand end by a pipe 69 to a reversing-valve 67, and at the right-hand end through valve mechanism 73 to a pipe 71 leading to the valve 67. The valve 73 is slidable in a casing 74 in a block 77, and in the position shown in Fig. 4, admits fluid under full pressure allowed by a throttle valve 75 to the right-hand end of cylinder 63 to give a rapid feed of the wheel up to the work. when the valve 73 is moved to the right, and admission of fluid is controlled by a coarse feed valve 83 in the block 77. The valve 73 is normally held in the position shown in Fig. 4, by means of a spring 97 compressed by a ring 98, which when released engages a flange 100 on the valve to move this to the right, the ring being held in the position shown by two pins 102 slidable in the block 77 and engaged by a lever 103 pivoted at 104 and engaged, through an adjustable screw 106, by a lever 107, pivoted at 108 and connected at 109 to the armature 110 of a solenoid 111. The circuit of the solenoid is closed by a contact member 116 on the armature 119 of a solenoid 120, the circuit of which is fed from a transformer 122 and is closed when the grinding-wheel 7 contacts with the work a, the wheel having been rendered conductive, for example, by impregnating it with an electrolyte, and the wheel head 3 being insulated from the slide 37. When the circuit of the solenoid 120 is closed, the contact member 116 is lifted, the circuit of solenoid 111 is opened and the valve 73 is moved to the right by the spring 97 so that grinding then proceeds at the coarse feed, until a cam 92 on the annular member 48 engages a roller 91 on a plunger 90 slidable in the block 77, thereby moving the valve 73 further to the right and causing fluid to pass to the cylinder 63 through a fine-feed valve 84 mounted in the block 77. Grinding then proceeds with the fine feed until a cam 93 on the member 48 engages the roller 91 when the valve 73 is closed except for the passage provided by fine grooves 139 in the part 138 of the valve, which gives almost negligible feeding for sparking out finish until a gauge causes axial separation of the work and wheel, and the valve 67 is moved to allow fluid to enter the left-hand end of the cylinder 63 to give rapid transverse separation of the wheel and the work. As the table 1 moves to the left, a cam 143 thereon engages the actuator 144 of a switch 127 opening the circuit of solenoid 120 to allow the circuit of solenoid 111 to be closed. Means is provided whereby, during axial separation of the work and wheel at completion of the grinding or for dressing the wheel, the cross slide is temporarily moved transversely to avoid " belt-mouthing " of the work.