Patent GB-1489968-A (GB)
Title: Tools and methods for machining bores
IPC: B24B33/08
Filed: 1975-12-19
Abstract: 1489968 Grinding NAGEL MASCHINENUND WERKZEUGFABRIK GmbH 19 Dec 1975 [21 Dec 1974] 52025/75 Heading B3D A tool for machining burrs comprises a tool body 14 and a working portion having an abrasive surface 16, the working portion being formed of a cylindrical zone 20 having a diameter corresponding to the required finished dimension of the bore and a conical or tapering zone 19 contiguous thereto in a direction towards the free end of the tool, and contiguous to the zone 19 a guide portion 18 constructed to guide the tool in a non-machined bore. In use, the tool is rotated and moved axially, the machining being effected in a single metalcutting stroke of the tool, fixedly adjusted to the finished dimension, into and out of the bore 12. The body 14 of the tool is tubular and has a reduced diameter portion having a coating 16 of abrasive, such as galvanically bonded diamond, the free end of the tool being closed by a screwed plug 15. The coating is of different thicknesses along the length of the reduced diameter portion so as to provide from the free end a cylindrical guide zone 18 dimensioned to enter the bore, the conical zone 19 which effects the main removal of material from the bore, and the cylindrical zone 20 which produces a finished surface on the bore, the abrasive being finer in the zone 20 than in the zones 18, 19. The difference in diameter between the zones 18, 20 is small and of the order of tenths of a millimetre. The coating of the cylindrical zone 20 is flush with the tool body above the zone and provides a further guide 35. The diameter of the cylindrical and conical zones is adjustable by axial movement of an expansion cone relative to a conical bore 23 in the tool body 14 which has a plurality of longitudinal slots 21 permitting expansion and contraction of the tool body. The diameter of the body is adjusted after a number of bores, e.g. 100, have been machined, the expansion cone being fixed to a rod 25 abutting a nut 26 adjustable on a screwthread 27 on the tool body. In use, the tool is rotated and the workpiece slipped manually on to the guide zone 18 which corresponds to the non-machined bore. Further advance of the tool causes the conical zone to effect the metal cutting and the cylindrical zone to finish the bore to the required size, the tool being advanced until the cylindrical zone has passed completely through the bore and then withdrawn. Coolant may be supplied to the machining location and to the interior of the tool so as to emerge through the slots 21. In another embodiment, the conical zone 19 is interrupted by circumferential, or one or more spiral, grooves. In a further embodiment, the tool body is held in a collet chuck of an adaptor and the rod 25 is secured to a member having a rod extending transversely of the adapter through axial grooves therein into an annular groove in a nut screw-threaded on to the body of the adapter. The adjustment of the cone by axial movement of the rod 25 may be effected manually or by a stepping mechanisn actuated by a device for measuring the finished workpieces. The abrasive coating may be directly mounted on the tool body, as shown, or on a plurality of separate bodies mounted on the periphery of the tool.