Spline (mechanical)

For the mathematical function, seeSpline (mathematics).

Asplineis a ridge or tooth on adrive shaftthat matches with agroovein a mating piece and transferstorqueto it, maintaining the angular correspondence between them.

For instance, agearmounted on a shaft might use a male spline on the shaft that matches the female spline on the gear. Adjacent images in the section below show a transmission input shaft with male splines and aclutchplate with mating female splines in the center hub, where the smooth tip of the axle would be supported in a pilot bearing in theflywheel(not pictured). An alternative to splines is akeyway and key,though splines provide a longerfatigue life,and can carry significantly greater torques for the size.

Types

There are several types of splines:

Parallel key spline

where the sides of the equally spaced grooves are parallel in both directions, radial and axial.

Involute spline

where the sides of the equally spaced grooves areinvolute,as with aninvolute gear,but not as tall. The curves increase strength by decreasingstress concentrations.

Crowned splines

where the sides of the equally spaced grooves are usually involute, but the male teeth are modified to allow for misalignment.

Serrations

where the sides of the equally spaced grooves form a "V". These are used on small-diameter shafts.

Helical splines

where the equally spaced grooves form ahelixabout the shaft. The sides may be parallel or involute. This can either minimize stress concentrations for a stationary joint under high load, or allow for rotary and linear motion between the parts.

Ball splines

where the grooves of the inner and outer parts are formed as linear races filled withball bearingsto allow for free linear motion even under high torque. To allow longer travel the outer spline can incorporate channels to re-circulate the balls, in this way torque can be transferred from a long shaft while travelling up or down the length.

• 
  Detail of a spline joint
• 
  A spline on the end of a manual transmission input shaft
• 
  Clutchdisc with splined hub to mesh with pictured input shaft
• 
  A drive shaft with a spline in the center anduniversal jointsat the ends to transmit torque and rotation and allow for changes in length
• 
  Splines on theCVend of an axle shaft
• 
  Matching splines of a bicycle cassette and freehub with a master spline visible at the top

Uses

Drive shafts on vehicles andpower take-offsuse splines to transmit torque and rotation and allow for changes in length. Splines are ubiquitous in aerospace, due to the spline's higher reliability and fatigue life compared to keyed shafts.

Splines are used in several places inbicycles.Thecrank arm to BB shaftinterfaces that are splined includeISIS Drive,TruvativGXP and Howitzer,Shimano'sOctalinkand many others, most of which are proprietary. Some cranksets feature modular spiders, where torque is transmitted through splines.Cassettesengage thefreehubvia a spline that has one groove wider than the others to enforce a fixed orientation.Disc brakemounting interfaces that are splined include Centerlock, by Shimano.

Aircraft enginesmay have a spline upon which mounts thepropeller.There may be a master spline which is wider than the others, so that the propeller may go on at only one orientation, to maintaindynamic balance.This arrangement is commonly found in larger engines, whereas smaller engines typically use a pattern of threaded fasteners instead.

Manufacturing

There are two complementary types of spline, internal and external. External splines may bebroached,shaped(for example on agear shapingmachine),milled,hobbed,rolled,groundorextruded.There are fewer methods available for manufacturing internal splines due to accessibility restrictions. Methods include those listed above with the exception of hobbing (no access). Often, with internal splines, the splined portion of the part may not have a through-hole, which precludes use of a pull / push broach or extrusion-type method. Also, if the part is small it may be difficult to fit a milling or grinding tool into the area where the splines are machined.

To prevent stress concentrations the ends of the splines arechamfered(as opposed to an abrupt vertical end). Such stress concentrations are a primary cause of failure in poorly designed splines.

See also

• Coupling
• Hirth joint
• Keyed joint
• Reeding

Further reading

• Robert Rich Robins (December 2008)."Tooth Engagement Evaluation of Involute Spline Couplings".Brigham Young University.Retrieved2010-07-08.