Gears
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Module 2- GEARS Lecture – 11 HELICAL GEARS Contents
11.1 Helical gears – an introduction 11.2 Helical gears – Kinematics 11.3 Helical gears – geometry and nomenclature 11.4 Helical gears – force analysis 11.5 Helical gears – bending stress 11.6 Helical gears – contact stress 11.7 Crossed helical gears 11.7.1 Tips for crossed helical gear design 11.1 HELICAL GEARS – an introduction In spur gears Fig.11.1 dealt earlier, the teeth are parallel to the axis whereas in helical gears Fig.11.2 the teeth are inclined to the axis. Both the gears are transmitting power between two parallel shafts.
Fig.11.1 Spur gear
Fig.11.2 Helical gear
Indian Institute of Technology Madras
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Helical gear can be thought of as an ordinary spur gear machined from a stack of thin shim stock, each limitation of which is rotated slightly with respect to its neighbours as in Fig.11.3. When power is transmitted both shafts are subjected to thrust load on the shaft.
Fig.11.3 Illustration of concept of helical gear
Fig.11.4 Double helical gear or herringbone gear
Indian Institute of Technology Madras
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Herringbone or double helical gear shown in Fig. 11.4 can be two helical gears with opposing helix angle stacked together. As a result, two opposing thrust loads cancel and the shafts are not acted upon by any thrust load. The advantages of elimination of thrust load in Herringbone gears, is obliterated by considerably higher machining and mounting costs. This limits their applications to very heavy power transmission.
Fig.11.5 Double helical gear of a cement mill rotary gear drive
Indian Institute of Technology Madras
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Fig. 11.6 Crossed helical gears. Crossed helical gears As in Fig. 11.6 are used for transmitting power between
Prof. K.Gopinath & Prof. M.M.Mayuram
Module 2- GEARS Lecture – 11 HELICAL GEARS Contents
11.1 Helical gears – an introduction 11.2 Helical gears – Kinematics 11.3 Helical gears – geometry and nomenclature 11.4 Helical gears – force analysis 11.5 Helical gears – bending stress 11.6 Helical gears – contact stress 11.7 Crossed helical gears 11.7.1 Tips for crossed helical gear design 11.1 HELICAL GEARS – an introduction In spur gears Fig.11.1 dealt earlier, the teeth are parallel to the axis whereas in helical gears Fig.11.2 the teeth are inclined to the axis. Both the gears are transmitting power between two parallel shafts.
Fig.11.1 Spur gear
Fig.11.2 Helical gear
Indian Institute of Technology Madras
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Helical gear can be thought of as an ordinary spur gear machined from a stack of thin shim stock, each limitation of which is rotated slightly with respect to its neighbours as in Fig.11.3. When power is transmitted both shafts are subjected to thrust load on the shaft.
Fig.11.3 Illustration of concept of helical gear
Fig.11.4 Double helical gear or herringbone gear
Indian Institute of Technology Madras
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Herringbone or double helical gear shown in Fig. 11.4 can be two helical gears with opposing helix angle stacked together. As a result, two opposing thrust loads cancel and the shafts are not acted upon by any thrust load. The advantages of elimination of thrust load in Herringbone gears, is obliterated by considerably higher machining and mounting costs. This limits their applications to very heavy power transmission.
Fig.11.5 Double helical gear of a cement mill rotary gear drive
Indian Institute of Technology Madras
Machine Design II
Prof. K.Gopinath & Prof. M.M.Mayuram
Fig. 11.6 Crossed helical gears. Crossed helical gears As in Fig. 11.6 are used for transmitting power between