Rotating spline
Encyclopedia
Splines are ridges or teeth
on a drive shaft that mesh with grooves in a mating piece and transfer torque
to it, maintaining the angular correspondence between them.
For instance, a gear
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.
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
, as with an involute gear
, but not as tall. The curves increase strength by decreasing stress concentration
s.
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 spline
s: where the 'teeth' of the outer part are implemented with a ball bearing
to allow for free linear motion even under high torque.
s use splines to transmit torque and rotation and allow for changes in length.
Splines are used in several places on bicycle
s. 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 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
s may have a spline upon which mounts the propeller
. 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, where smaller engines typically use a pattern of threaded fasteners instead.
(for example on a gear shaping machine), milled
, hobbed
, rolled, ground
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 chamfer
ed (as opposed to an abrupt vertical end). Such stress concentrations are a primary cause of failure in poorly designed splines.
on a drive shaft that mesh with grooves in a mating piece and transfer torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
to it, maintaining the angular correspondence between them.
For instance, a gear
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
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
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
plate, while the smooth tip of the axle is supported in the pilot bearing in the flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...
. An alternative to splines is a keyway and key, though splines provide a longer fatigue life.
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
Involute
In the differential geometry of curves, an involute is a curve obtained from another given curve by attaching an imaginary taut string to the given curve and tracing its free end as it is wound onto that given curve; or in reverse, unwound. It is a roulette wherein the rolling curve is a straight...
, as with an involute gear
Involute gear
The involute gear profile is the most commonly used system for gearing today. In an involute gear, the profiles of the teeth are involutes of a circle. In involute gear design contact between a pair of gear teeth occurs...
, but not as tall. The curves increase strength by decreasing stress concentration
Stress concentration
A stress concentration is a location in an object where stress is concentrated. An object is strongest when force is evenly distributed over its area, so a reduction in area, e.g. caused by a crack, results in a localized increase in stress...
s.
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
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
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 spline
Ball spline
Ball splines are a special type of linear motion bearing that are used to provide nearly frictionless linear motion while allowing the member to transmit torque simultaneously. There are grooves ground along the length of the shaft for the recirculating ground balls to run inside...
s: where the 'teeth' of the outer part are implemented with a ball bearing
Ball bearing
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 by using at least two races to contain the balls and transmit...
to allow for free linear motion even under high torque.
Uses
Drive shafts on vehicles and power take-offPower take-off
A power take-off or power takeoff is a splined driveshaft, usually on a tractor or truck, that can be used to provide power to an attachment or separate machine. It is designed to be easily connected and disconnected...
s use splines to transmit torque and rotation and allow for changes in length.
Splines are used in several places on bicycle
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
s. The crank arm to BB shaft
Crankset
The crankset or chainset , is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain, which in turn drives the rear wheel...
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 engage the freehub
Freehub
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism, and the name freehub is a registered trademark of Shimano. A set of sprockets are mounted onto a splined shaft of the freehub to engage the chain...
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
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
s may have a spline upon which mounts the propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
. 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, where smaller engines typically use a pattern of threaded fasteners instead.
Manufacturing
There are two types of splines, internal and external. External splines may be broached, shapedGear shaper
A gear shaper is a machine tool for cutting the teeth of internal or external gears. The name shaper relates to the fact that the cutter engages the part on the forward stroke and pulls away from the part on the return stroke, just like the clapper box on a planer shaper.The cutting tool is also...
(for example on a gear shaping machine), milled
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
, hobbed
Hobbing
Hobbing is a machining process for making gears, splines, and sprockets on a hobbing machine, which is a special type of milling machine. The teeth or splines are progressively cut into the workpiece by a series of cuts made by a cutting tool called a hob...
, rolled, ground
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
or extruded
Extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
. 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 chamfer
Chamfer
A chamfer is a beveled edge connecting two surfaces. If the surfaces are at right angles, the chamfer will typically be symmetrical at 45 degrees. A fillet is the rounding off of an interior corner. A rounding of an exterior corner is called a "round" or a "radius"."Chamfer" is a term commonly...
ed (as opposed to an abrupt vertical end). Such stress concentrations are a primary cause of failure in poorly designed splines.