One’s teeth of a helical gear are set at an angle (relative to axis of the gear) and take the shape of a helix. This allows one’s teeth to mesh steadily, starting as point get in touch with and developing into collection contact as engagement progresses. One of the most noticeable advantages of helical gears over spur gears is less noise, especially at medium- to high-speeds. Also, with helical gears, multiple tooth 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, to ensure that vibrations, shock loads, and wear are reduced.
But 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 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 in combination with spur gears. The axial forces vary in proportion to the helical gear china magnitude of the tangent of the helix angle. Although larger helix angles offer higher acceleration and smoother movement, the helix angle is typically limited to 45 degrees because of the creation of axial forces.