Splines are ridges or teeth on a drive shaft that matches with grooves in a mating piece and transfer

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of t ...

to it, maintaining the angular correspondence between them. For instance, a

gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic p ...

mounted on a shaft might use a male spline on the shaft that matches the female spline on the gear. The splines on the pictured drive shaft match with the female splines in the center of the clutch plate, while the smooth tip of the axle is supported in the pilot bearing in the flywheel. An alternative to splines is a keyway and key, though splines provide a longer fatigue 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 are

involute In mathematics, an involute (also known as an evolvent) is a particular type of curve that is dependent on another shape or curve. An involute of a curve is the locus of a point on a piece of taut string as the string is either unwrapped from o ...

, as with an involute gear, but not as tall. The curves increase strength by decreasing stress 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 a

helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined hel ...

about 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 with

ball bearings A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this ...

to 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. File:Spline-shaft.png, Detail of a spline joint File:Splinedshaft.jpg, A spline on the end of a manual transmission input shaft Image:Clutchdisc.jpg, Clutch disc with splined hub to mesh with pictured input shaft Image:Cardan Shaft.jpg, A drive shaft with a spline in the center and universal joints at the ends to transmit torque and rotation and allow for changes in length File:2008-04-23 Axle splines.jpg, Splines on the CV end of an axle shaft File:Cassetteandfreehub.jpg, Matching splines of a bicycle cassette and freehub with a master spline visible at the top

Uses

Drive shafts on vehicles and power take-offs use 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 in bicycles. The crank arm to BB shaft interfaces that are splined include ISIS Drive, Truvativ GXP and Howitzer, Shimano's Octalink and many others, most of which are proprietary. Some cranksets feature modular spiders, where torque is transmitted through splines.

Cassettes Cassette may refer to: Technology * Cassette tape (or ''musicassette'', ''audio cassette'', ''cassette tape'', or ''tape''), a worldwide standard for analog audio recording and playback ** Cassette single (or "Cassingle"), a music single in the ...

engage the freehub via a spline that has one groove wider than the others to enforce a fixed orientation. Disc brake mounting interfaces that are splined include Centerlock, by Shimano.

Aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years ma ...

s may have a spline upon which mounts the

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

. There may be a master spline which is wider than the others, so that the propeller may go on at only one orientation, to maintain dynamic 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 splines, internal and external. External splines may be broached, shaped (for example on a gear shaping machine), milled, hobbed, rolled,

ground Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...

or extruded. 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 are chamfered (as opposed to an abrupt vertical end). Such stress concentrations are a primary cause of failure in poorly designed splines.

Types

Uses

Manufacturing

See also

References

Further reading