One’s teeth of a helical gear are set at an angle (relative to axis of the apparatus) and take the shape of a helix. This enables one’s teeth to mesh steadily, starting as point get in touch with and developing into line get in touch with as engagement progresses. Probably the most noticeable advantages of helical gears over spur gears is certainly less noise, especially at medium- to high-speeds. Also, with helical gears, multiple the teeth are at all times in mesh, which means much less load on every individual tooth. This results in a smoother changeover of forces in one tooth to the next, so that vibrations, shock loads, and wear are reduced.
But 
the inclined angle of the teeth also causes sliding contact between the teeth, which generates axial forces and heat, decreasing performance. 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 require thrust or roller bearings, which are typically larger (and more costly) than the simple bearings used in combination with spur gears. The axial forces vary compared to the magnitude of the helical gear china tangent of the helix angle. Although bigger helix angles provide higher swiftness and smoother movement, the helix angle is typically limited by 45 degrees because of the production of axial forces.