The teeth of a helical gear are set at an angle (in accordance with axis of the apparatus) and take the shape of a helix. This enables one’s teeth to mesh steadily, starting as point contact and developing into series contact as engagement progresses. One of the most noticeable advantages of helical gears over spur gears can be less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple the teeth are always in mesh, which means much less load on every helical gear china individual tooth. This outcomes in a smoother changeover 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 your teeth, which creates axial forces and heat, decreasing efficiency. These axial forces enjoy a significant function 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 usually larger (and more expensive) than the simple bearings used in combination with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although bigger helix angles provide higher speed and smoother motion, the helix angle is typically limited by 45 degrees due to 
the creation of axial forces.
