GB396339A - Improvements in hobs for cutting worm wheel teeth - Google Patents

Abstract

396,339. Gear-cutting hobs. HOLROYD & CO., Ltd., J. and WALKER, H., Perseverance Works, Harbour Lane, Milnrow, near Rochdale. March 30, 1933, No. 9546. [Class 83 (iii).] The teeth of a hob for cutting worm wheels are provided on a number of separate coaxial members which may be relatively adjustable either angularly or axially. In Fig. 1 a shaft 1 carries a circular row of integral hob teeth 2 while an axially adjustable ring 3, slidably keyed to the shaft, has a similar row of teeth 4. The cutting edges 8, 9 of each tooth 2 and the corresponding edges 10, 11 of each tooth 4 of the other row may lie on helical surfaces corresponding to the surfaces of a worm intended to mesh with the worm wheel to be cut. With this disposition the tooth bases 2<1>, 4<1> are disposed as in Fig. 4, a being the lead of the worm. The number of teeth of each circular row is equal to the number of threads of the worm. To produce the hob, the teeth are first cut to the required lead while the rows are spaced by a washer 14 and the requisite number of gashes are cut. To provide side clearance, a thinner washer 16, Fig. 5, is substituted and the tooth sides are cut by a tool or grinding wheel set to give a shorter lead b corresponding to the new positions of the teeth, Fig. 5. The distance between the two rows of teeth is then increased by substituting a thicker washer and side relief on the opposite tooth flanks is produced in a similar manner. The usual top clearance is also provided. For using the hob, the washer 14 is replaced so that the teeth assume the position, Fig. 7, wherein the relieved cutting edges have the required lead a. To restore the effective cutting thickness d after repeated sharpenings, a thinner washer 18 is substituted, Fig. 8, so that the tooth gaps are now cut by the edge 9<1> of a tooth of one row and the opposite edge 10<1> of a tooth of the other row. The edges 8<1>, 11<1> take roughing cuts. In a modification, the hob may be initially provided with teeth thinner than the standard, in which case the setting shown in Fig. 8 will be required. In another modification Fig. 2, each circular row of teeth may be formed on a separate ring keyed to the cutter shaft and retained by a locking ring. In a further modification, the hob teeth are provided on rings which are relatively adjustable angularly for providing side clearance and for restoring the cutting thickness after sharpening. In some cases, the hob may have more than two rows of teeth.