Worm gear Here worm and worm wheel have different teeth profile. It can transmit very high mechanical power or torque. A helical gear has teeth in the form of a helix around the gear. Power transmission capability of helical gear is comparatively small. The Boeing 747 has a wingspan of 65 meters and AR of 7.7. Hobbing can also be used for cutting helical gears. Differences between these four types of gear based on various factors are explained below. A gear drive is one engagement type rigid mechanical drive that is suitable for small distance power transmission. Axial thickness is the distance parallel to the axis between two pitch line elements of the same tooth. apex The pressure angle variesfrom amaximum at the beginningof the engagement, reduces tozero at the pitch pointand again increases to amaximum at the end of engagementresulting in the less smooth running of the gears. This ratio is obtained most directly as the ratio of the length of action to the base pitch. transmit power between two parallel shafts. Spur gear Since the teeth are parallel to the gear axis, it imposes only radial force to the bearings. //