Cutting gear teeth: Slicing straight teeth is definitely comparatively easier than slicing helical teeth. Equipment milling or gear hobbing can be used to cut tooth of spur and helical gears. In milling, just two simultaneous motions are wanted to cut the teeth of spur gears; however, three simultaneous motions are necessary for cutting teeth of helical gear.

Influence load, vibration and noise: Since teeth of two mating spur gears will come in sudden contact, so they encounter a shock or influence load. This also produces significant vibration and noise, which sometimes impose limit on maximum permissible speed of procedure. On the contrary, gradual contact between mating teeth results a gradual load on one’s teeth and lower vibration and noise. Thus helical gears can be employed at higher rate without much problem.

Contact situation between mating teeth: Spur gears have straight teeth parallel to gear axis. Two mating gears are also mounted in parallel shafts. Thus tooth of two mating spur gears can be found in sudden contact and the contact is always a line of duration equals to teeth face width. On the contrary, helical gears have helical teeth and they are mounted on parallel shafts. So teeth of two mating helical gears can be found in gradual contact. Their engagement begins with a spot and becomes a collection and then gradually disengages as a spot. So contact length does not remain constant.

Orientation of driver and driven shafts: One basic advantage of gear drive over other mechanical drives (like belt or chain drive) is its possibility to use for nonparallel shafts. However, various kinds gear are ideal for various orientations of driver and driven shafts. Both spur equipment and helical gears are overwhelmingly utilized for parallel shafts; whereas, bevel gears can be utilized for intersecting shafts and worm gear can be utilized for perpendicular nonintersecting 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 fairly similar to worm gear; however, crossed helical gear cannot offer high velocity decrease. Typically, it is suitable for 1:1 to at least one 1:2 quickness ratio (as compared to 1:15 to 1 1:100 in worm gear). Its application can be limited because of many limitations.