Cutting gear teeth: Reducing straight teeth is usually comparatively easier than slicing helical teeth. Equipment milling or gear hobbing can be utilized to cut the teeth of spur and helical gears. In milling, just two simultaneous motions are desired to cut the teeth of spur gears; however, three simultaneous motions are required for cutting the teeth of helical gear.
Effect load, vibration and noise: Since teeth of two mating spur gears will come in sudden contact, so they experience a shock or impact load. This also produces significant vibration and noise, 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 noise. Thus helical gears may be employed at higher rate without much problem.
Contact scenario between mating teeth: Spur gears have directly teeth parallel to equipment axis. Two mating gears are also mounted in parallel shafts. Thus tooth of two mating spur gears come in sudden contact and the get in touch with is always a type of length equals to teeth encounter width. On the other hand, helical gears possess helical teeth and they are mounted on parallel shafts. So tooth of two mating helical gears come in gradual contact. Their engagement starts with a spot and becomes a range and then steadily disengages as a spot. 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 the probability to use for nonparallel shafts. However, various kinds gear are ideal for different orientations of driver and driven 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 utilized for perpendicular non-intersecting shafts. There is a particular type of helical equipment, called crossed helical equipment, which can be useful for transmitting power between perpendicular 
shafts. This is fairly similar to worm gear; however, crossed helical equipment cannot offer high velocity reduction. Typically, it really is suitable for 1:1 to 1 1:2 velocity ratio (as compared to 1:15 to 1 1:100 in worm gear). Its application can be limited due to many limitations.