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Difference between spur and helical gears(2014-02-18)

Spur Gear Vs Helical Gears

Gears are set of toothed wheels that mesh with one another to transmit / change torque, speed and direction of the power source. By altering the gear ratio one can increase or decrease speed or torque from the power source. Gears are used in almost all mechanical devices and more commonly used in automobiles.

Spur and helical are two types of gears, which are circular with teeth pointing radially out. In a Spur Gear the teeth are straight-cut and the edge of the teeth is parallel to the axis of rotation. In a Helical Gear the teeth are cut at an angle and the edge of the teeth is non parallel to the axis of rotation. There are fundamental differences in their design, which decides their functionality and application.


Spur Gear can be used only in a transmission involving parallel orientation; the gears can be meshed correctly only if they are perfectly parallel to each other. A Helical Gear on the other hand can be meshed in parallel or cross orientation. In cross orientation the input and the resultant shafts are not parallel and thus allowing transmission in more than one axis.


Spur Gears are comparatively more efficient than Helical gears. This is due to more number of teeth engaged at any point in time and a greater sliding friction in a Helical Gear. Also Helical Gears have a resultant thrust along the axis, which is often accommodated by having a thrust bearing, reducing the overall efficiency of the system.


The angled teeth in Helical Gears engage more gradually, each pair of teeth makes a point contact and gradually increases its contact and finally disengages at a single point. Spur Gear makes a sudden line contact and thus creating a higher noise.


The higher noise of Spur Gear restricts it to low speed application where the noise produced are manageable. Helical Gears can be used of high speed applications, where noise control is important.

Load bearing:

Helical Gears can handle higher load than Spur Gear. With more number of teeth engaged at any point in time, allows it to bear higher load by sharing it between the teeth’s.

Manufacturing cost:

Spur Gears are comparatively simple in design and thus costs less. Helical Gears with its angled tooth involves complex manufacturing process.


Helical Gears are most commonly used in automobile gear boxes, as they operate with less noise at higher speeds. Spur Gears can be most commonly seen in fuel pumps, mills and in mechanical watches.

Difference between Spur and Helical gears:

  • Both Spur and Helical Gears are circular in shape.
  • Teeth in Spur Gear are straight-cut, in helical it is at and angle.
  • Spur Gear can be used only in parallel orientation, whereas Helical Gears can also be used in cross orientation.
  • Spur Gears are more efficient than helical due to lesser friction.
  • Helical Gears produce lesser noise compared to spur gears and thus used for hight speed application.
  • Spur Gears are easy and are less expensive to manufacture.
  • Helical Gear has higher load bearing capacity than a Spur Gear.