GB794912A - Improvements in or relating to single-start or multiple-start hobs - Google Patents

Abstract

794,912. Milling-cutters. LINDNER, W. March 11, 1955 [March 12, 1954], No. 7288/55. Class 83 (3). A single-start or multi-start hob, which may be of conical form, for cutting gears, splines, &c., comprises cutting-teeth 1-26 grouped in rows along the helical threads B, E of the hob, the distance between consecutive teeth of a group on the same thread (e.g. teeth 1-6 on thread B), being substantially equal, and the gap between the first tooth of one group (e.g. tooth 7) and the last tooth of the preceding group on the same thread (tooth 6) being equal to from one to five times the average helical pitch of the teeth in all the groups, the gap being measured, along the pitch-cylinder of the hob, between the nearest adjacent points on the teeth 6, 7. The twostart hob of Fig. 5 has three groups of teeth 1-6, 7-12, 13-26, on each thread B, E provided on toothed rings L, M, N, the first and second groups effecting rough-cuts and the third group a finishing-cut. The height of the teeth in groups 1-6, 7-12 increases from the first to the last tooth in the group, and the height of tooth 7 is less than that of tooth 6, teeth 13-26 being of constant height. Succeeding teeth of the first and second groups 1-6, 7-12, cut alternate sides of a tooth-space, and the cutting edges are relieved, Fig. 7, and notched at H to break the chips. The finishing- teeth 13-26 operate on both flanks of the tooth spaces, and their width increases over the leading-teeth. A different cutting angle is provided on each group of teeth, and the groups may be sharpened in stages on their own supporting sleeve 33, Fig. 8, in the case of a builtup hob with toothed rings 30-32. In this event, rings 30, 31 are removed to enable the teeth on ring 32 to be sharpened, and the latter ring removed and rings 30, 31 replaced so that these may be sharpened simultaneously. A key 41 on each of the rings 30, 31 engages in a keyway 40 in the sleeve 33 to locate the rings during the grinding of one flank angle, and one of the rings is re-positioned to engage its key in a keyway 39, Fig. 9 (not shown), during the grinding of the other flank-angle. The keys 41 are engaged in the keyways 39, 40 during operation of the cutter.