Helical Gear Vs Herringbone Gear Vs Double Helical Gear

Helical Gear Vs Herringbone Gear Vs Double Helical Gear

Helical Gear	Herringbone Gear
Teeth of the helical gear are cut in the form of a helix (either left hand or right hand helix) on the cylindrical gear blank.	Identical teeth are cut in two halves of the gear blank maintaining same module, number of teeth and helix angle but opposite hand of helix.
A pair of mating helical gears produces significant radial thrust force.	Thrust force produces by each half of the gear is equal and opposite in direction; and thus they cancel out each other.
Radial thrust force limits the helix angle to a maximum of about 25°.	Absence of thrust force gives the provision to use higher helix angle (up to about 45°).
Bearings that can handle both axial load and thrust load are required to use with helical gear.	Since thrust force does not exist, so bearings that can handle heavy radial load can be used with herringbone gear.
Power transmission capability of helical gear is comparatively small.	It can transmit very high mechanical power or torque.
Design and manufacturing of helical gear is easier and thus it is cheap.	Herringbone gear is expensive because of complicated design and manufacturing.

Herringbone Gear Vs Double Helical Gear

Herringbone Gear	Double Helical Gear
In herringbone gear, no gap is provided between two halves. So teeth with left hand helix touches the teeth with right hand helix.	In double helical gear, small relief gap is provided between two halves. So teeth with left hand helix do not touch the teeth with right hand helix.
Its manufacturing is difficult and requires dedicated machine.	Its manufacturing is comparatively easy as it can be cut by hobbing, shaping or even milling.
It has less axial length and thus can be used where space is limited.	Other features being same, it requires more axial space due to presence of relief gap.