Cutting gear teeth: Slicing straight teeth can be comparatively easier than reducing helical teeth. Gear milling or gear hobbing can be utilized to cut the teeth of spur and helical gears. In milling, just two simultaneous motions are wanted to cut tooth of spur gears; nevertheless, three simultaneous motions are required for cutting tooth of helical gear.
Effect load, vibration and sound: Since teeth of two mating spur gears comes in sudden contact, so they encounter a shock or effect load. This also generates significant vibration and sound, which occasionally impose limit on optimum permissible speed of operation. On the contrary, 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 acceleration without much problem.
Contact scenario between mating teeth: Spur gears have directly 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 contact and the contact is always a line of length equals to teeth face width. On the other hand, helical gears possess 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 range and then steadily disengages as a spot. So contact length will 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, several types of gear are suitable for different orientations of driver and driven shafts. Both spur gear and helical gears are overwhelmingly used for parallel shafts; whereas, bevel gears can be utilized for intersecting shafts and worm gear can be used 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 pretty similar to worm equipment; however, crossed helical gear cannot provide high velocity decrease. Typically, it is suitable for 1:1 to 1 1:2 acceleration ratio (in comparison with 1:15 to 1 1:100 in worm gear). Its application is also limited because of many limitations.