Cutting gear teeth: Trimming straight teeth is usually comparatively easier than cutting helical teeth. Equipment milling or gear hobbing can be utilized to cut the teeth of spur and helical gears. In milling, only two simultaneous motions are desired to cut tooth of spur gears; however, three simultaneous motions are required for cutting tooth of helical gear.
Effect load, vibration and sound: Since teeth of two mating spur gears will come in sudden contact, therefore they encounter a shock or effect load. This also generates significant vibration and sound, which sometimes impose limit on maximum permissible speed of procedure. On the contrary, gradual get in touch with between mating teeth results 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 situation between mating teeth: Spur gears have directly teeth parallel to gear axis. Two mating gears are also mounted in parallel shafts. Thus tooth of two mating spur gears come in sudden contact and the contact is always a line of duration equals to teeth face width. On the other hand, helical gears possess helical teeth plus they are mounted on parallel shafts. So the teeth of two mating helical gears come in gradual contact. Their engagement starts with 
a point and becomes a collection and then steadily disengages as a spot. So contact length will 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 its likelihood to use for nonparallel shafts. However, several types of gear are ideal for various orientations of driver and driven shafts. Both spur equipment 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 kind of helical gear, called crossed helical gear, which can be useful for transmitting power between perpendicular shafts. This is very similar to worm equipment; however, crossed helical equipment cannot offer high velocity decrease. Typically, it is suitable for 1:1 to 1 1:2 acceleration ratio (when compared with 1:15 to at least one 1:100 in worm gear). Its application is also limited due to many limitations.