The standard tooth profile, generated as a point on a taut line unwrapping from the base circle. Two involute gears transmit motion at a constant speed ratio, and that ratio does not change if the center distance shifts slightly, which makes the form forgiving to build and mount. Involute teeth can also be generated by a straight-sided rack cutter, which is why hobs and rack cutters have straight flanks.
Profile trace shows the involute's fine through the middle, the problem's all in the tip relief.
Because involute flanks can be generated by a straight-sided rack, one hob cuts every tooth count of the same pitch and pressure angle.
Also heard as
- involute curve
- involute profile
Related terms
Base circle
The circle from which the involute tooth profile is unwound, smaller than the pitch circle.
Line of action
The straight path along which the point of tooth contact travels, tangent to both base circles.
Rack
A straight bar with gear teeth along it, which turns a pinion's rotation into straight-line travel.
Profile deviation
How far a tooth's actual shape from root to tip departs from the intended involute and modifications.