The fundamental purpose of the strength calculation is a responsible design, choosing the right gear characteristics and derived from that their dimensions, all in function of the transferring powers or capabilities in particular operating conditions; thus for existing gears or proposed characteristics, the power transmission capacity and to verify the feasibly lifetime or to capture this approximately.
This is equivalent with defining of materials and gears that, for a given or assumed load will avoid that tooth failure or tooth flank damage occur, and accordingly will ensure or promise an adequate service life. It goes without saying that a good solution provides a reasonable safety factor and heavy or too big gears, which are often expensive and sometimes lead to useless high circumferential speeds, can be avoided. If the strength calculation of gears seems fairly complicated, this is mainly due to the shape of the teeth, to the movement that brings a continual changing of the powers, to their distribution, as also to define the difficulty of the maximum load, the influence of the inertia forces and the influence of the mounting conditions.
On the other hand, the errors are inherent to the teeth themselves (roundness, eccentricity, pitch errors, direction or profile error) and the degree of finish of the tooth flank and other elements that directly impact the behaviours of a gear and which one should take into account, but that ultimately are difficult to convert in numbers. Taking into account the changing of the load and operating conditions, with the multitude of factors that affect the gear pair, it is clear that the resistance of a teeth, both against fracture or wear, and for a given material is not proportional to the size of a tooth (section of tooth foot and facewidth), but also to a large extent depends on the speed, the tooth shape (profiles), the contact line and the quality of finish.
Trying to make a direct link between these factors and the power transmission capacity for a certain life span, was a complicated task for which eminent researchers and practitioners have made efforts. It is a question of drawing up a simple and rational calculation method, tested against a large number of trials, observations, verifications and comparisons of behaviors of gears, in very diverse and spreaded out operating conditions. The so acquired experience has allowed to draw up formulas in which all resistance determinant factors are included with corresponding appropriate coefficients.
Thanks to the help of computer programs, nowadays it has become possible to calculate in a quick way the gear sets according to the different standards. When problems arise, we can always calculate or design gear sets or gearboxes for you.