1,163,719. Lapping. J. BARRAGAN. 1 Dec., 1966 [18 Aug., 1966], No. 53821/66. Heading B3D. A surface lapping machine in which workpieces to be lapped are confined in rings placed on a rotatable bed of the machine and retained by arms of a stepwise rotatable device disposed in star formation, the angular extent of the steps of the motion of the rotatable device allowing the substitution of one ring by another at the periphery of the bed, and in which at least one plane, smooth table is disposed close to the periphery of the bed to permit the feeding of a ring to, and the withdrawal of a ring from, the bed by sliding, comprises (a) Means securing said rotatable device to a ratchet wheel; (b) A rotatable disc coaxial with the ratchet wheel; (c) Means limiting rotation of said disc to an angle equal to the angular extent of said steps; . (d) A pawl mounted on said disc and adapted to co-operate with the ratchet wheel; and (e) Means urging said disc to rotate in the direction opposite to the direction of rotation of the bed, said disc being more freely rotatable in the direction opposite to the direction of rotation of the bed than in the direction of rotation of the bed. A base (1) carries an annular table 2 surrounding a circular, flat, horizontally disposed bed 3 rotated by a motor housed in the base (1). Cylindrical rings 4 resting on the bed 3 contain the workpieces; these may be in contact with one another and the wall of the ring, may be arranged in cavities in a circular plate, or may be loaded by heavy covers 5 with handles 5a. Arms 8 each having two rollers 9 bearing against a ring 4 restrain the rings 4 from being carried round by the bed 3. Each arm 8 is secured to a jaw 12 of a three-jaw chuck 11 secured on a shaft 10; the jaws are displaceable radially by rotating the operating shaft 13 of the chuck by a square key. The flatness of the lopped workpieces is periodically checked optically, and the arms 8 radially adjusted accordingly to correct any curvature of the surface of the bed 3. At its upper end the shaft 10 is supported, through a height adjusting nut 15 and ball support 16, by a bracket 14. The shaft 10 has a bore 17 with a funnel 18 at the upper end to which abrasive in liquid suspension is supplied from the adjustable outlet 21 of a tube 20 carried in a support 22; the liquid suspension passes through a tube 19 to the bed 3. A ratchet wheel 24 is keyed to the shaft 10, and a disc 25 is rotatably mounted on the hub 24a of the ratchet wheel. A pawl 26 slidable in a radial groove in the disc 25 is engageable with the ratchet wheel 24 and has a tooth 26a engaging a notch 30a in a drum 30 rotatable by a handle 32 about a shaft 31 carried by the disc 25. The outer end of the pawl comprises a head 26b co-operating with an arcuate guide 34 to limit outward displacement of the pawl and a guide 35 tangential to the disc 25. A gap 36 in the periphery of the disc 25 receives a stop 37 fixed to the bracket 14, the angular extent of the gap less the angular width of the stop corresponding to the angular pitch of the teeth of the ratchet wheel, i.e. 60 degrees. The disc 25 is urged to rotate in the opposite direction to rotation of the bed 3 by a cable 38 carrying a weight 40. A portion 42 of the periphery of the disc 25 is toothed and meshes with a toothed sector 43 on a shaft 44. A pinion 45 on the shaft 44 meshes with a rack 47 on a piston 48 movable in a liquid filled cylinder 46. The ends of the cylinder are connected by a conduit 49 containing, in parallel, a non-return valve 50 and a constriction 51 adjustable by a knob 52. Operation.-With the bed 3 rotating in the direction of arrow F, the machine lapping workpieces in the three rings 4 and the pawl 26 in engagement with a radial flank of a tooth of the ratchet wheel 24, the thrust exerted by the rings 4 on the arms 8 tends to rotate the disc 25 in the direction of the arrow F so pressing the flank 36a of the gap 38 against the stop 37. When the handle 32 is actuated to withdraw the pawl 26 the weight 40 drives the disc 25 in the direction opposite to the arrow F; the piston 48 displaces liquid in the direction of opening of the valve 50, so that the disc 25 turns freely and the flank 36b of the gap 36 rapidly approaches the stop 37. The guide 35 drives the pawl 26 inwardly to engage the next notch of the ratchet wheel 24 whereupon the disc 25 may be driven by the ratchet wheel in the direction of the arrow F; the piston 48 displaces liquid through the constriction 51 to give hydraulic braking so that the advance through one step of the arms 8 is effected slowly, avoiding shocks and centrifugal force. Movement of the disc 25, upon liberation of the pawl 26, being rapid it is not necessary, in order to advance one step, to stop rotation of the bed 3 since the pawl 26 returns into engagement with the ratchet wheel before the assembly fixed to the shaft 10 has acquired acceleration. For safety reasons, the motor driving the bed 3 may be stopped as soon as withdrawal of pawl 26 commences, and the bed restarted only when the pawl has returned into engagement with the ratchet wheel and the flank 36b touches the stop 37; to this end, the pawl 26 is fixed to a curved bar 55 which acts on the push-button of a switch 56 in the supply to the bed driving motor, the length of the bar 55 being such that it frees the switch button only when the pawl has returned into engagement with the ratchet wheel. Two tables 57, 58 are mounted on the table 2 spaced 60 degrees apart around the bed 3. Each table comprises a sheet of hardened glass or of a smooth polished ceramic resting on four height-adjusting screws 60, the sheet being held down on the screws by spring-loaded draw members. The edges of the tables facing the bed are shaped to correspond to the curved edge of the bed; they may be lapped to the desired shape by contact with the edge of the bed 3 with abrasive interposed. The unloading table 57 is slightly below the bed 3. The loading table 58 may be above the bed and may be provided with a handle (65) so that after it has been used to feed a loaded ring on to the bed it may be spaced from the bed so as not to interfere with the edge of a ring which projects beyond the edge of the bed.