Cutting gear teeth: Trimming straight teeth is usually comparatively easier than reducing helical teeth. Gear milling or equipment hobbing can be used to cut the teeth of spur and helical gears. In milling, just two simultaneous motions are desired to cut tooth of spur gears; however, three simultaneous motions are necessary for cutting the teeth of helical gear.
Effect load, 
vibration and sound: Since teeth of two mating spur gears will come in sudden contact, so they experience a shock or influence load. This also generates significant vibration and sound, which sometimes impose limit on maximum permissible speed of procedure. On the other hand, gradual contact between mating teeth outcomes a gradual load on one’s teeth and lower vibration and sound. Thus helical gears may be employed at higher rate without much problem.
Contact situation between mating teeth: Spur gears have directly teeth parallel to equipment axis. Two mating gears are also mounted in parallel shafts. Thus teeth of two mating spur gears can be found in sudden get in touch with and the contact is always a type of duration equals to teeth face width. On the other hand, helical gears have helical teeth plus they are installed on parallel shafts. So tooth of two mating helical gears can be found in gradual contact. Their engagement starts with a point and becomes a series and then gradually disengages as a point. So contact length will not remain constant.
Orientation of driver and driven shafts: One fundamental advantage of equipment drive over other mechanical drives (like belt or chain drive) is its probability to use for non-parallel shafts. However, various kinds gear are ideal for various orientations of driver and driven shafts. Both spur gear and helical gears are overwhelmingly used 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 type of helical gear, called crossed helical gear, which can be employed for transmitting power between perpendicular shafts. This is pretty similar to worm equipment; however, crossed helical gear cannot offer high velocity decrease. Typically, it really is suitable for 1:1 to 1 1:2 velocity ratio (when compared with 1:15 to 1 1:100 in worm gear). Its application can be limited due to many limitations.