Cutting gear teeth: Reducing straight teeth can be comparatively easier than cutting helical teeth. Equipment milling or gear hobbing can be used to cut teeth of spur and helical gears. In milling, only two simultaneous motions are wanted to cut the teeth of spur gears; however, three simultaneous motions are required for cutting tooth of helical gear.
Impact load, vibration and noise: Since teeth of two mating spur gears will come in sudden contact, so they experience a shock or impact load. This also creates significant vibration and noise, which sometimes impose limit on optimum permissible speed of operation. On the contrary, gradual get in touch with between mating teeth outcomes a gradual load on one’s teeth and lower vibration and sound. Thus helical gears may be employed at higher acceleration without much problem.
Contact scenario between mating teeth: Spur gears have directly teeth parallel to equipment axis. Two mating gears are also mounted in parallel shafts. Thus tooth of two mating spur gears come in sudden get in touch with and the get in touch with is always a type of size equals to teeth encounter width. On the contrary, helical gears have helical teeth and they are mounted on parallel shafts. So tooth of two mating helical gears come in gradual get in touch with. Their engagement begins with a spot and becomes a range and then gradually disengages as a spot. So contact length does not remain constant.
Orientation of driver and driven shafts: One fundamental advantage of gear drive over other mechanical drives (like belt or chain drive) is the possibility to use for nonparallel 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 utilized for intersecting shafts and worm equipment can be utilized for perpendicular non-intersecting shafts. There exists a particular type of helical gear, called crossed helical equipment, which can be employed for transmitting power between perpendicular shafts. This is fairly similar to worm equipment; however, crossed helical equipment cannot offer high velocity reduction. Typically, it really is suitable for 1:1 to 1 1:2 quickness ratio (in comparison with 1:15 to at least one 1:100 in worm gear). Its application can be limited due to many limitations.