The teeth of a helical gear are set at an angle (relative to axis of the apparatus) and take the shape of a helix. This allows one’s teeth to mesh steadily, 
starting as point contact and developing into series get in touch with as engagement progresses. One of the most planetary gearbox noticeable advantages of helical gears over spur gears is definitely less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple teeth are at all times in mesh, this means less load on every individual tooth. This results in a smoother transition of forces from one tooth to the next, to ensure that vibrations, shock loads, and wear are reduced.
But the inclined angle of one’s teeth also causes sliding contact between the teeth, which generates axial forces and heat, decreasing performance. These axial forces play a significant part in bearing selection for helical gears. Because the bearings have to endure both radial and axial forces, helical gears require thrust or roller bearings, which are usually larger (and more costly) compared to the simple bearings used with spur gears. The axial forces vary compared to the magnitude of the tangent of the helix angle. Although bigger helix angles offer higher acceleration and smoother motion, the helix angle is typically limited to 45 degrees due to the production of axial forces.