A spline is a ridge or tooth on a

drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power, torque, and rotation, usually ...

that matches with a

groove Groove or Grooves may refer to: Music * Groove (music) * Groove (drumming) * The Groove (band), an Australian rock/pop band of the 1960s * The Groove (Sirius XM), a US radio station * Groove 101.7FM, a former Perth, Australia, radio station ...

in a mating piece and transfers

torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...

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

gear A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or ...

mounted 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 a

clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...

plate with mating female splines in the center hub, where the smooth tip of the axle would be supported in a pilot bearing in the

flywheel A flywheel is a mechanical device that uses the conservation of angular momentum to store rotational energy, a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, a ...

(not pictured). 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 (mathematics), locus of a point on a piece of taut string as the string is eith ...

, 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 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 A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...

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

bicycle A bicycle, also called a pedal cycle, bike, push-bike or cycle, is a human-powered transport, human-powered or motorized bicycle, motor-assisted, bicycle pedal, pedal-driven, single-track vehicle, with two bicycle wheel, wheels attached to a ...

s. The crank arm to BB shaft interfaces that are splined include

ISIS Drive The bottom bracket on a bicycle connects the crankset (chainset) to the bicycle and allows the crankset to rotate freely. It contains a spindle to which the crankset attaches, and the bearings that allow the spindle and crankset to rotate. The ...

, 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 engage the freehub via a spline that has one groove wider than the others to enforce a fixed orientation.

Disc brake A disc brake is a type of brake that uses the #Calipers, calipers to squeeze pairs of #Brake pads, pads against a disc (sometimes called a rakerotor) to create friction. There are two basic types of brake pad friction mechanisms: abrasive f ...

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. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbin ...

s may have a spline upon which mounts the

propeller A propeller (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 a working flu ...

. 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 spline, internal and external. External splines may be broached, shaped (for example on a gear shaping machine), milled, hobbed, rolled, ground or

extruded Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex ...

. 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