Cutting gear teeth: Trimming 
straight teeth is comparatively easier than cutting helical teeth. Equipment milling or equipment hobbing can be used 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 tooth of helical gear.
Effect load, vibration and noise: Since teeth of two mating spur gears will come in sudden contact, so they encounter a shock or effect load. This also creates significant vibration and sound, which occasionally impose limit on optimum permissible speed of operation. 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 can be employed at higher quickness 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 tooth of two mating spur gears come in sudden get in touch with and the contact is always a type of duration equals to teeth encounter width. On the contrary, helical gears possess helical teeth plus they are installed on parallel shafts. So teeth of two mating helical gears can be found in gradual get in touch with. Their engagement begins with a point and becomes a series and then gradually 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 its likelihood to use for non-parallel shafts. However, several types of gear are suitable for varying orientations of driver and powered shafts. Both spur gear and helical gears are overwhelmingly utilized for parallel shafts; whereas, bevel gears can be used 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 quite similar to worm equipment; however, crossed helical equipment cannot provide high velocity decrease. Typically, it really is suitable for 1:1 to 1 1:2 quickness ratio (as compared to 1:15 to at least one 1:100 in worm gear). Its application can be limited because of many limitations.