One’s teeth of a helical gear are set at an angle (in accordance with axis of the apparatus) and take the form of a helix. This allows one’s teeth to mesh gradually, starting as point contact and developing into line contact as engagement progresses. Probably the most noticeable advantages of helical gears over spur gears is usually less noise, especially at medium- to high-speeds. Also, with helical gears, multiple the teeth are often in mesh, which means less load on each helical gear china individual tooth. This results in a smoother transition of forces in one tooth to the next, so 
that vibrations, shock loads, and wear are reduced.
However the inclined angle of one’s teeth also causes sliding get in touch with between the teeth, which creates axial forces and heat, decreasing effectiveness. These axial forces enjoy a significant part in bearing selection for helical gears. As the bearings have to endure both radial and axial forces, helical gears need thrust or roller bearings, which are usually larger (and more expensive) 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 larger helix angles provide higher speed and smoother movement, the helix angle is typically limited to 45 degrees because of the production of axial forces.