Patent GB-816275-A (GB)
Title: Rotary magnetic work holders
IPC: B23Q3/154
Filed: 1957-07-22
Abstract: 816,275. Magnets. TAFT-PEIRCE MANUFACTURING CO. July 22, 1957 [July 30, 1956], No. 23086/57. Class 35. [Also in Group XXIII] A rotary magnetic workholder comprises a body 14, Fig. 1, having at least two members 27, 35 of magnetic material spaced from each other by means 36 having appreciable reluctance, and a source 44 of magnetic lines of force which is axially-movable between two positions in a bore 29 in the body so that in one position the flux passes through a workpiece 42 disposed on the faces of the members 27, 35 and in the other position the flux is shunted through the body. The body is driven by a face-plate 12 from a machine spindle 11 and is formed of a part 26 and the member 27 secured together by screws 28 and separated from the member 35 by a brass ring 36. Magnets 44 are carried in a brass sleeve 45 which is slidable in the bore 29 of the body under the control of a rod 20, at one end, screwthreaded into a polepiece 46 secured to the magnets, and, at the other end, provided with a grooved collar 22 engaged by a pin 24 on a pivoted lever 25; the lever or the rod may be operated by a solenoid or air cylinder. The magnets and polepiece 46 are secured by a non- magnetic bolt 52 to a front polepiece 49 which has a shunt portion 50 so arranged that when the magnets are moved to the forward operative position by the rod 20 the flux passes from the magnets through the portion 50 into the member 35 and workpiece 42 and back through the other member 27 and body 14 into the rear polepiece 46 and magnets 44. In the rearward inoperative position the shunt portion 50 is disposed adjacent the member 27 and the flux from the magnets passes directly into the body 14 to the rear polepiece and magnets. A pin 47 engages a slot 48 in the rear polepiece to provide limiting positions of movement of the magnets. Wear on the faces of the members may be prevented by non-magnetic radial inserts 43 of hard material such as tungsten-carbide. The ring 35 may be in the form of a circular plate spaced with its rear face adjacent the polepiece 49 when the latter is in its forward position. In an embodiment suitable for holding smaller diameter workpieces the front polepiece 149, Fig. 4, has a portion 57 of reduced diameter which when the magnets 44 are in the forward position is disposed adjacent a ring 135 separated from the member 127 of the body 114 by a non-magnetic ring 136. The flux from the magnets then passes through the portion 57 into the ring 135 and workpiece 42 and back into the member 127 and body 114 to the rear polepiece 146 and magnets. In the forward position the shunt portion 50 of the front polepiece 149 is separated from the body by an annular air chamber 55 while in the rearward position it is disposed adjacent the part 126 of the Lody 114 and passes the flux from the magnet directly into the body and to the rear polepiece and magnets as before; the portion 57 is in the rearward position disposed adjacent the non- magnetic ring 136 and therefore inoperative. In an embodiment suitable for holding workpieces 142, 242, Fig. 6, of differing diameters, a plurality of magnets 244 are disposed in circumferentially spaced holes 61 in a cylindrical body 60 of non-magnetic material axiallyslidable in an outer body 214. A rear polepiece 246, which magnetically connects the magnets to the outer body, and a front polepiece 257 having a shunt plate 249 are connected to the spider by a non-magnetic bolt 252. Alternate sector-shaped plates 227, 235, are associated with the magnets and separated from each other by non-magnetic strips 66, Fig. 7, which may be of brass or wear-resistant tungsten material. The plates 227 are in direct magnetic contact with the body 214 but separated from the polepiece 257 by arcuate non-magnetic strips 64, and the plates 235 are magnetically insulated from the body 214 by non-magnetic plates 68 and provided with arcuate non-magnetic strips 65 which permit direct magnetic contact between the plates and polepieces only when the magnets are in the forward operative position. In this position the shunt plate 249 is disposed adjacent a non-magnetic ring 69 and the flux passes from the magnets through the polepiece 257 into the plates 235 and workpiece, and back through the adjacent plates 235 and body 214 into the polepiece 246 and magnets 244. In the rearward inoperative position the shunt plate is in direct contact with the body 214 through which the flux passes into the rear polepiece and magnets, and the polepiece 257 is magnetically insulated from the plates 235 by the strips 65. The strips may be brazed together and the plates 68 brazed to the ring 69 or the plates 227, 235 may be brazed together or undercut so that the parts are held together when the plates are secured to the body 214. The non-magnetic parts of the embodiments may be moulded from plastic material such as epoxy-resin composition.