Involute Splines
A spline is a set of narrow generated longitudinally around the circumference of a shaft or grooves generated on the inside bore of a workpiece. The externally splined shaft mates with an internal spline that slots, or spaces, formed in the reverse of the shaft’s teeth. These keyways are implemented in a design to prevent movement between two parts, especially while in the transmission of torque. Splines transfer the rotary motion of an input to an output through a mechanical connection, or splined shaft. Splines that are not an involute tooth form are called serrations. Splines can also be used to center a rotor to the shaft. Splines have several different types of applications. Splines are used while coupling shafts when relatively heavy torques are to be transmitted with slippage, transmitting power to floating or permanently fixed gears, and coupling parts that may require frequent removal for indexing or change of angular position. External and internal splines are very extensively used in the automotive, machine tools and other industries.
Involute splines are the predominant form of splines because they are stronger than straight sided splines and are easier to cut and the fit. Involute splines have teeth similar to gear teeth except spline teeth are much shorter, and they do not roll. The external splines can be formed either by hobbing are by a spline shaper. Internal splines can be formed by broaching or a spline shaper. The various simplest method of initially selecting an involute spline based on a shaft diameter is to arrive at an initial pitch circle diameter in module. Involute splines are used for fixed end for sliding connections of shafts with hubs. While splines are used in the transmission of power similar to gears, this feature of splines is not tied to the involute profile that splines also share with gears. The involute profile is due to the manufacturing techniques for the splines.
Involute splines are available in several standard pressure angles. The 30 degree pressure angle spline are the most commonly used pressure angle. The pressure angle measurement of splines are similar to gears, and splines are generally inspected in the same ways that external and internal gears are inspected, typically through measurement over or between pins. Measurement over or between pins is when specific sized wires are placed in between gear teeth across from one another and the distance between the outside of the wires is then measured with micrometers. This measurement can also tell you if the gear has the proper gear tooth profile. Unlike gears, the tooth thicknesses of splines are measured in actual and effective tooth thickness. The effective sizes of tooth thickness are affected by errors such as involute profile error, lead error and errors in the spacing of spline teeth and keyways. This effective tooth thickness has led to an industry practice of designing splines around the parameter that between 25-50% of the spline’s teeth will be engaged during coupling and therefore carry the load. This load is generally practiced to be uniformly distributed.
Variations in spline teeth clearances can cause some of the spline teeth to engage before other teeth while coupling cause those teeth to carry a much greater load than other teeth. This ultimately means that these teeth will fail faster than others. Splines have precision teeth that transferred torque from the shaft to a hub as the flanks of the teeth mesh. These teeth are spaced uniformly around the entirety of the shaft and create an increased load capacity in the system. Unlike gears, splines are designed to allow a shaft to engage with a hub over its full circumference and therefore creating a constant multiple teeth point of contact in order to transmit torque.
Spline cutting is the process of machining internal or external splines on shafts, gears and other mechanical power transmission components, which mesh with grooves in a mating piece allowing power to be transmitted from one to another. Splines are generally manufactured through the use of hobbing or shaper cutting for external spline teeth and via shaping or broaching for internal spline teeth. Marples Gears manufactures precision splines both internal and external. We have a dedicated staff that manufacture and inspect your spline projects.
