A Spline by definition are ridges or teeth on a drive shaft which mesh with grooves in a mating piece. This is done so as to transfer torque whilst maintaining angular correspondence. This provides an equally distributed load along the sides of the teeth, enabling a longer fatigue life as compared to a keyway drive. Both Splined Shaft and Mating piece rotate together at a ratio of 1:1, and splined shafts will have their ends chamfered so as to prevent stress concentrations.
Splined Shafts are common in a variety of transport vehicles. In the automotive sector demand has grown for higher rotational speeds and torque delivery which cannot be met by Key Shafts. Slots cut into a Key Shaft would weaken it and reduce its torque transmitting capacity. Aircraft engines often mount their propeller on a Master Spline which ensures it can only spin in one direction and maintain dynamic balance. Even on Bicycles, splined shafts can be found so as to enforce fixed orientation.
Types of Spline
There are two key varieties of Splines; Internal and External. These are almost always used in combination with each other. There are a few different designs of External Splines including broached, shaped, milled, hobbed, rolled, ground and extruded. There are a few variations on this:
Involute Splines are the most commonly found. They have equally spaced teeth, but as its name suggests these teeth are involute, and usually a shorter form of spline. This lowered height decreased stress concentration and lowers the possibility of cracks due to fatigue. Involute spines are self-centering under load and even where an assembly is loose fitting will center themselves when torque is applied.
Parallel Key Splines are also equally spaced and have straight-sided grooves that are parallel in design. This design is similar to a Keyway Drive but where in that case the Keys are fitted into slots, here they are an integral part of the shaft and are equally spaced along the circumference.
Serrated Splines are most often used on smaller diameter shafts and have teeth in a triangular or ‘V’ formation, allowing for more teeth on a smaller circumferences. Often used in gearboxes.
Helical Splines have equally spaced teeth which form a helix around the shaft. This design enables the better load sharing of rotational torque along the length of the shaft and is most often used in high torque applications.
Bronte Precision are a sub-contract manufacturer with a speciality in both Gear Cutting and the Splining of Shafts. We are ISO accredited and based in Bradford, West Yorkshire.