Spur Gears: are the most recognized style of gear. Spur Gears are used primarily to transmit rotary motion between parallel shafts, while maintaining uniform speed and torque. The involutes tooth form, being the simplest to generate, Permits high manufacturing tolerances to be attained.


Helical Gears: are similar to spur gears with the exception that the teeth are cut at an angle to the axis of the shaft (helix angle). The helix cut creates a wider contact area enabling higher strengths and torques to be achieved. Though helical Gear sets operate quieter and smoother than spur gears, they are slightly less Efficient. Helical gears can run on parallel shafts or may be offset as much as the Helix angle will permit. Axial thrust loads are developed during operation and must be considered when selecting bearings and mounting arrangements.


Internal Spur Gears: unlike spur gears, have the teeth generated on the I.D. of the blank. They are generally stronger and more efficient than the mating pinion gear. The pitch diameter of the internal gear must be at least 1.5 times the P.D. of The mating pinion. If this condition is not met, interferences between the tips of the Teeth will occur. Internal gears provide the designer with the ability to achieve Higher contact and drive ratios than standard spur gears at shorter center Distances. They also enable a velocity change without a directional change. This would require an idler gear with standard spurs.