Cutting gear teeth: Reducing straight teeth is certainly comparatively easier than slicing helical teeth. Gear milling or gear hobbing can be used to cut teeth of spur and helical gears. In milling, just 
two simultaneous motions are wanted to cut teeth of spur gears; nevertheless, 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, therefore they encounter a shock or effect load. This also generates significant vibration and sound, which sometimes impose limit on maximum permissible speed of procedure. On the contrary, gradual get in touch with between mating teeth results a gradual load on one's teeth and lower vibration and noise. Thus helical gears may be employed at higher quickness without much problem.
Contact situation between mating teeth: Spur gears have directly 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 get in touch with and the contact is always a type of length equals to teeth encounter 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 starts with a spot and becomes a range and then steadily disengages as a point. So contact length does not remain constant.
Orientation of driver and driven shafts: One basic advantage of equipment drive over other mechanical drives (like belt or chain drive) is its probability to use for nonparallel shafts. However, several types of gear are suitable for different 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 equipment can be used for perpendicular nonintersecting shafts. There exists a particular kind of helical gear, called crossed helical equipment, 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 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.