Cutting gear teeth: Trimming straight teeth is certainly comparatively easier than cutting helical teeth. Gear milling or equipment hobbing can be used to cut the teeth of spur and helical gears. In milling, only two simultaneous motions are wanted to cut the teeth of spur gears; nevertheless, three simultaneous motions are necessary for cutting tooth of helical gear.
Influence load, vibration and sound: Since teeth of two mating spur gears comes in sudden contact, therefore they experience a shock or impact load. This also produces significant vibration and noise, which sometimes impose limit on optimum permissible speed of procedure. On the other hand, gradual contact between mating teeth results a gradual load on one’s teeth and lower vibration and noise. Thus 
helical gears may be employed at higher velocity 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 get in touch with is always a type of duration equals to teeth face width. On the other hand, helical gears have helical teeth plus they are mounted on parallel shafts. So tooth of two mating helical gears can be found in gradual contact. Their engagement begins with a point and becomes a collection and then gradually disengages as a point. So contact length does 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 the probability to use for nonparallel shafts. However, various kinds gear are ideal for varying orientations of driver and driven shafts. Both spur gear and helical gears are overwhelmingly utilized for parallel shafts; whereas, bevel gears can be utilized for intersecting shafts and worm gear can be used for perpendicular non-intersecting shafts. There is a particular kind of helical equipment, called crossed helical equipment, 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 decrease. Typically, it really is suitable for 1:1 to at least one 1:2 rate ratio (as compared to 1:15 to 1 1:100 in worm gear). Its application can be limited because of many limitations.