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 gradually, starting as point contact and developing into range contact as engagement progresses. Probably the most noticeable benefits of helical gears over spur gears is definitely less noise, planetary gearbox especially at medium- to high-speeds. Also, with helical gears, multiple the teeth are at all times in mesh, this means less load on each individual tooth. This results in a smoother transition of forces from one tooth to another, to ensure that vibrations, shock loads, and wear are reduced.
However the inclined angle of one’s teeth also causes sliding contact between your teeth, which produces axial forces and heat, decreasing efficiency. These axial forces play a significant role 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 expensive) 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 provide higher acceleration and smoother motion, the helix angle is typically limited by 45 degrees because of the production of axial forces.