Cutting gear teeth: Slicing straight teeth is certainly comparatively easier than trimming helical teeth. Equipment milling or gear hobbing can 
be utilized to cut teeth of spur and helical gears. In milling, only two simultaneous motions are desired to cut teeth of spur gears; nevertheless, three simultaneous motions are required for cutting teeth of helical gear.
Impact load, vibration and noise: Since teeth of two mating spur gears comes in sudden contact, so they experience a shock or effect load. This also generates significant vibration and sound, which occasionally impose limit on optimum permissible speed of operation. 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 velocity without much problem.
Contact scenario between mating teeth: Spur gears have straight 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 line of duration equals to teeth face width. On the other hand, helical gears have helical teeth and they are installed on parallel shafts. So the teeth of two mating helical gears can be found in gradual contact. Their engagement starts with a point and becomes a line and then gradually disengages as a spot. So contact length will 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 possibility to use for non-parallel shafts. However, several types of gear are ideal for various orientations of driver and driven shafts. Both spur gear and helical gears are overwhelmingly used 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 type of helical gear, called crossed helical equipment, which can be employed for transmitting power between perpendicular shafts. This is quite similar to worm equipment; however, crossed helical equipment cannot offer high velocity decrease. Typically, it really is suitable for 1:1 to at least one 1:2 swiftness ratio (as compared to 1:15 to at least one 1:100 in worm gear). Its application can be limited due to many limitations.