Cutting gear teeth: Reducing straight teeth is usually comparatively easier than reducing helical teeth. Gear milling or gear hobbing can be used to cut the teeth of spur and helical gears. In milling, only two simultaneous motions are desired to cut the teeth of spur gears; however, three simultaneous motions are required for cutting teeth of helical gear.
Effect load, vibration and noise: Since teeth of two mating spur gears comes in sudden contact, therefore they encounter a shock or effect load. This also generates significant vibration and sound, which sometimes impose limit on optimum permissible speed of operation. On the other hand, gradual contact between mating teeth results a gradual load on the teeth and lower vibration and noise. Thus helical gears may be employed at higher velocity without much problem.
Contact scenario between mating teeth: Spur gears have straight teeth parallel to equipment axis. Two mating gears are also mounted in parallel shafts. Thus tooth of two mating spur gears come in sudden contact and the get in touch with is always a line of duration equals to teeth encounter width. On the other hand, helical gears have helical teeth plus they are mounted on parallel shafts. So teeth of two mating helical gears come in gradual contact. Their engagement starts with a spot and becomes a series and then steadily disengages as a point. So contact length does not remain constant.
Orientation of driver and driven shafts: One simple advantage of equipment drive over other mechanical drives (like belt or chain drive) is the possibility to use for non-parallel shafts. However, various kinds gear are suitable for different orientations of driver and driven shafts. Both spur equipment and helical gears are overwhelmingly utilized for parallel shafts; whereas, bevel gears can be used for intersecting shafts and worm equipment can be utilized for perpendicular nonintersecting shafts. There exists a particular kind of helical gear, called crossed helical gear, which can be employed for transmitting power between perpendicular shafts. This is very similar to worm gear; however, crossed helical equipment cannot offer high velocity decrease. Typically, it is suitable for 1:1 to 1 1:2 acceleration ratio (in comparison with 1:15 to at least one 1:100 in worm gear). Its application is also limited due to many limitations.