One’s teeth of a helical gear are set at an angle (in accordance with axis of the gear) and take the form of a helix. This enables the teeth to mesh steadily, starting as point contact and developing into series get in touch with as engagement progresses. One of the most noticeable benefits of helical gears over spur gears is less noise, especially at medium- to high-speeds. Also, with helical gears, multiple teeth are generally in mesh, which means much less load on every individual tooth. This outcomes in a planetary gearbox smoother changeover of forces in one tooth to the next, 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 generates axial forces and heat, decreasing performance. These axial forces play a significant part in bearing selection for helical gears. As the bearings have to endure 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 
compared to the magnitude of the tangent of the helix angle. Although larger helix angles provide higher velocity and smoother movement, the helix angle is typically limited to 45 degrees due to the production of axial forces.
