Cutting gear teeth: Slicing straight teeth is comparatively easier than cutting helical teeth. Equipment milling or equipment hobbing can be used to cut tooth of spur and helical gears. In milling, only two simultaneous motions are wanted to cut tooth of spur gears; nevertheless, three simultaneous motions are necessary for cutting teeth of helical gear.
Impact load, vibration and sound: Since teeth of two mating spur gears comes in sudden contact, therefore they experience a shock or effect load. This also creates significant vibration and noise, which occasionally impose limit on maximum permissible speed of procedure. On the other hand, gradual contact between mating teeth outcomes a gradual load on the teeth and lower vibration and sound. Thus helical gears may be employed at higher speed without much problem.
Contact situation between mating teeth: Spur gears have straight teeth parallel to equipment axis. Two mating gears are also installed in parallel shafts. Thus the teeth of two mating spur gears come in sudden get in touch with and the contact is always a type of length equals to teeth face width. On the contrary, helical gears have helical teeth plus they are installed on parallel shafts. So teeth of two mating helical gears come in gradual contact. Their engagement begins with a spot and becomes a line and then gradually disengages as a spot. So contact length does not remain constant.
Orientation of 
driver and driven shafts: One simple advantage of gear drive over other mechanical drives (like belt or chain drive) is the likelihood to use for non-parallel shafts. However, various kinds gear are suitable for various orientations of driver and driven shafts. Both spur gear and helical gears are overwhelmingly utilized for parallel shafts; whereas, bevel gears can be used for intersecting shafts and worm equipment can be used for perpendicular non-intersecting shafts. There is a particular kind 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 provide high velocity reduction. 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 because of many limitations.