Straight bevel Straight bevel gears are the most common type of bevel gear, where teeth will be straight like teeth in case of spur gear but teeth will be taper from larger diameter of tooth to the smaller diameter of tooth in case of straight bevel gear. Shaping and coniflex, these are two cutting methods, those are used to cut the straight bevel gear teeth to prepare the straight bevel gear. 100 % straight teeth in straight bevel gears are not acceptable in many applications as they will not permit any misalignment during assembly with gearbox. Therefore there will be slightly curvature in teeth of straight bevel gear and that is termed as crowning.
Now solution of this problem will be to cut and prepare the curved teeth for bevel gear so that the engagement of teeth of mating gear will be gradual and higher tooth to tooth contact as compared to straight bevel gearing. Spiral bevel gear will provide the silent operation as compared to straight bevel gearing. Spiral bevel gears are the best choice to use where applications are associated with high rpm and high torque. Spiral bevel gears are normally preferred to use to transmit the power and motion between driving and driven shafts those are typically at ninety degree orientation with each other.