Law of gearing says that the common normal at the point of contact between a pair of teeth must always pass through the pitch point.

The face and flank of involute teeth are generated by a single curve where as in cycloidal

The two non-intersecting and non-parallel i.e. non-coplanar shaft connected by gears. These gears are called skew bevel gears or spiral gears and the arrangement is known as skew bevel gearing or spiral gearing. This type of gearing also have a line contact, the rotation of which about the axes generates the two pitch surfaces known as hyperboloids.

Pitch circle is an imaginary circle which by pure rolling action, would give the same motion as the actual gear.

ηmax = cos (θ + φ ) + 1/ cos (θ − φ ) + 1

None.

Addendum is the radial distance of a tooth from the pitch circle to the top of the tooth.

When equal bevel gears (having equal teeth) connect two shafts whose axes are mutually perpendicular, then the bevel gears are known as mitres.

The fundamental condition of correct gearing is the common normal at the point of contact between a pair of teeth must always pass through the pitch point.

The theoretical minimum value for the contact ratio is one, that is there must always be at least one pair of teeth in contact for continuous action.