Cutting gear teeth: Cutting straight teeth is definitely comparatively easier than cutting helical teeth. Gear milling or gear hobbing can be utilized to cut 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 necessary for cutting the teeth of helical gear.
Influence load, vibration and sound: Since teeth of two mating spur gears comes in sudden contact, so they experience a shock or impact load. This also produces significant vibration and sound, which sometimes impose limit on maximum permissible speed of operation. On the other hand, gradual get in touch with between mating teeth results a gradual load on the teeth and lower vibration and sound. Thus helical gears may be employed at higher swiftness 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 the teeth of two mating 
spur gears can be found in sudden get in touch with and the get in touch with is always a line of duration equals to teeth face width. On the contrary, helical gears possess helical teeth and they are installed on parallel shafts. So the teeth of two mating helical gears come in gradual get in touch with. Their engagement starts with a spot and becomes a range and then gradually disengages as a point. 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 probability to use for nonparallel shafts. However, several types of gear are ideal for various orientations of driver and powered shafts. Both spur gear and helical gears are overwhelmingly used for parallel shafts; whereas, bevel gears can be utilized for intersecting shafts and worm equipment can be used for perpendicular non-intersecting shafts. There exists a particular type of helical equipment, called crossed helical gear, which can be employed for transmitting power between perpendicular shafts. This is quite similar to worm gear; however, crossed helical equipment cannot offer high velocity reduction. Typically, it is suitable for 1:1 to at least one 1:2 rate ratio (when compared with 1:15 to at least one 1:100 in worm gear). Its application is also limited because of many limitations.