One’s teeth of a helical gear are set at an angle (relative to axis of the gear) and take the form of a helix. This enables the teeth to mesh steadily, starting as point get in touch with and developing into line get in touch with as engagement planetary gearbox progresses. One of the most noticeable benefits of helical gears over spur gears is usually less noise, especially at medium- to high-speeds. Also, with helical gears, multiple teeth are usually in mesh, which means much less load on each individual tooth. This results in a smoother changeover of forces from one tooth to the next, so that vibrations, shock loads, and wear 
are reduced.
However the inclined angle of the teeth also causes sliding get in touch with between your teeth, which generates axial forces and heat, decreasing efficiency. These axial forces perform a significant part in bearing selection for helical gears. Because the bearings have to endure both radial and axial forces, helical gears need thrust or roller bearings, which are typically larger (and more expensive) than the simple bearings used with spur gears. The axial forces vary compared to the magnitude of the tangent of the helix angle. Although bigger helix angles provide higher acceleration and smoother motion, the helix position is typically limited to 45 degrees due to the creation of axial forces.