Cutting gear teeth: Trimming straight teeth is usually comparatively easier than cutting helical teeth. Gear milling or gear hobbing can be utilized to cut teeth of spur and helical gears. In milling, only two simultaneous motions are wanted to cut teeth of spur gears; however, three simultaneous motions are required for cutting teeth of helical gear.

Impact load, vibration and sound: Since teeth of two mating spur gears comes in sudden contact, therefore they experience a shock or influence load. This also generates significant vibration and noise, which sometimes impose limit on optimum permissible speed of operation. On the contrary, gradual get in touch with between mating teeth results a gradual load on the teeth and lower vibration and noise. Thus helical gears can be employed at higher swiftness 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 the teeth of two mating spur gears come in sudden contact and the get in touch with is always a line of size equals to teeth face width. On the contrary, helical gears possess 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 range and then gradually disengages as a point. So contact length does 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 probability to use for non-parallel shafts. However, several types of gear are ideal for different 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 gear, called crossed helical gear, which can be employed for transmitting power between perpendicular shafts. This is quite similar to worm gear; however, crossed helical gear cannot provide high velocity decrease. Typically, it is suitable for 1:1 to at least one 1:2 swiftness ratio (when compared with 1:15 to 1 1:100 in worm gear). Its application can be limited because of many limitations.