{"data":{"fields":"term_definition","term_definition":"<div class=\"definition\">Gear failure can occur due to tooth breakage (tooth stress) or surface failure (surface durability) as a result of fatigue and wear. Strength is determined in terms of tooth-beam stresses for static and dynamic conditions, following well established formula and procedures. Satisfactory results may be obtained by the use of Barth\u2019s Revision to the Lewis Formula, which considers beam strength but not wear. The formula is satisfactory for commercial gears at Pitch Circle velocities of up to 1500 FPM. METALLIC SPUR GEARS W= Tooth Load, Lbs. (along the pitch line) S= Safe Material Stress (static) Lbs. per Sq. In. (Table II) F= Face Width, In. Y= Tooth Form Factor (Table I) P= Diametral Pitch D= Pitch Diameter V= Pitch Line Velocity, Ft. per Min. = .262xDxRPM For NON-METALLIC GEARS, the modified Lewis Formula shown below may be used with (S) values of 6000 PSI for Phenolic Laminated material.<\/div>"}}