by Aleksey Alekseevich
gear image of Orlando Florin Rosu from Fotolia.com
Spur and helical gears are two different types of mechanical gears. A spur gear is circular and its teeth point directly from the center. A worm gear is also circular, but its teeth are molded at an angle to spiral downward from the gear. There are fundamental differences in their respective designs that would make one more suitable than the other for a certain task, and because of these differences the gears are not interchangeable on the same machine.
Spur gears are more efficient than helical gears. Helical gears are less efficient because they have more teeth that touch when two gears are connected, increasing friction and increasing energy loss from heat.
Spur gears cost less to manufacture than helical gears. The design of a spur gear is simpler and easier to create than a worm gear, which reduces the cost of production.
Helical gears can withstand a higher load than spur gears. As the load is distributed among more teeth, a worm gear can carry more load than a spur gear.
Helical gears are more durable than spur gears. The load is distributed over more teeth, so for a given load, helical gears will be able to distribute force better than a spur gear, reducing wear on individual teeth.
Helical gears are quieter than spur gears. Helical gears experience less vibration due to the angled teeth and, as a result, generate less noise.