Cylindrical gears are the most common type of manufactured gear. They are typically usedfor low and medium speeds because at high speeds, if they are not rectified, or corrected,they produce a variable noise.
Helical gears are characterised by an oblique angle in relation to the axis of rotation. Theaxis can be parallel or can crossover, generally at 90º. Helical gears have the advantageof being able to transmit more speed and power than spur gears, they are quieter and lastlonger. However they experience more wear and tear and need more lubrication than spurgears.