SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Accuracy of hobbing is normally high for pitch and for helix provided machines are maintained, involute is dependent solely 节 on the accuracy of the hob profile. As the involute form is generated by as many cuts as there are gashes on the hob the involute is not exact, but if there are, say, 14 tangents generating a flank of 20 mm radius of curvature about 4 mm high the divergence from a true involute is only about half a micron, hob manufacturing and mounting errors can be above 10 microns Use of tostart hobs or oblique hobbing gives increased error levels since hob errors of pitching transfer to the cut gear Broaching拉削 spline花键 Broaching is not usually used for helical gears but is useful for internal spur gears; the principal use of broaching in this context is for internal splines, which cannot easily be made by any other method. As with all broaching the method is onl economic for large quantities since setup costs are highSCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Accuracy of hobbing is normally high for pitch and for helix, provided machines are maintained, involute is dependent solely on the accuracy of the hob profile. As the involute form is generated by as many cuts as there are gashes on the hob the involute is not exact, but if there are, say, 14 tangents generating a flank of 20 mm radius of curvature about 4 mm high the divergence from a true involute is only about half a micron, hob manufacturing and mounting errors can be above 10 microns. Use of twostart hobs or oblique hobbing gives increased error levels since hob errors of pitching transfer to the cut gear. Broaching Broaching is not usually used for helical gears but is useful for internal spur gears; the principal use of broaching in this context is for internal splines, which cannot easily be made by any other method. As with all broaching the method is only economic for large quantities since setup costs are high. 周 节 拉削 spline 花键