The teeth of a helical gear are set at an angle (relative to axis of the gear) and take the form of a helix. This enables one’s teeth to mesh steadily, starting as point contact and developing into range contact as engagement progresses. One of the most noticeable advantages of helical gears over spur gears can be less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple the teeth are always in mesh, which means much less load on every individual tooth. This results in a smoother transition of forces in one tooth to the next, so that vibrations, shock loads, and wear are reduced.
However the inclined angle of the teeth also causes sliding get in touch with between the teeth, which creates axial forces and heat, decreasing efficiency. These axial forces enjoy a significant function in bearing selection for helical gears. As the bearings have to withstand both radial and axial forces, helical gears need thrust or roller bearings, which are typically larger (and more costly) than the simple bearings used with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although larger helix angles offer higher speed and smoother motion, the helix angle is typically limited to 45 gear rack degrees because of the creation of axial forces.