One’s 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 gradually, starting as point get 
in touch with and developing into series get in touch with as engagement progresses. One of the most noticeable advantages of helical gears over spur gears is usually less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple the teeth are always in mesh, this means much less load on each individual tooth. This results in a smoother changeover of forces in one tooth to another, to ensure that vibrations, shock loads, and wear are reduced.
But the inclined angle of the teeth also causes sliding get in touch with between the teeth, which generates axial forces and heat, decreasing efficiency. These axial forces perform a significant function in bearing selection for helical gears. Because the bearings have to endure both radial and axial forces, helical gears need gear rack thrust or roller bearings, which are usually larger (and more expensive) than the simple bearings used with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although larger helix angles provide higher rate and smoother movement, the helix position is typically limited by 45 degrees due to the production of axial forces.