| 摘要 |
302,510. Olson, C. G. Jan. 16, 1928. Gear-cutting; milling-cutters. - A hob 10 for cutting spur gears and the like is provided with gashes 14 oblique to the hob thread and disposed so as to increase the sharpness of the cutting-edge of the leading side 16 of the teeth, and the teeth ere arranged to generate on a circle smaller than the pitch circle 30, Fig. 3, of the blank. The teeth are a,so undercut so as to increase the acutaness of the top cutting-edge 18. The pressure angle of the blank teeth is shown at a in Fig. 3. According to the invention, the inclination of the flanks of a hob tooth is less than the pressure angle of the gear to be cut and is equal to an angle #. The hob will thus generate on a circle 30<1> and the hob teeth are thinner at the base and thicker at the top than the teeth of an ordinary hob. The lead is also slightly shorter than that of the normal hob. In some cases, particularly for roughing out, doublethreaded hobs may be employed. This modification of the hob profile results in a better distribution of the work performed by the leading and leaving edges 16, 17 respectively, this distribution being indicated in Fig. 5. From this it is seen that the acute angled leading edge removes approximately 25 per cent of the metal while the obtuse-angled leaving edge 17 is only required to remove 15 per cent of the metal, the corresponding figures for ordinary hobs being 20 per cent and 30 per cent respectively. |
