Involute Spline Calculation App

This app calculate the shear stress, contact stress and safety factors of a involute spline shaft under a defined torque. This calculation gives a good direction on design and will help to define sizes and lengths of shafts, and therefore the parts that are assembled on it. Bearings, Seals, snap rings sizes will, in most cases, be defined by the spline torque capacity.
The calculation is based in the document released by Darle W. Dudley, and used in many different engineering books.
The geometry of the inner diameter and the outer diameter is approximated for a quality 6 spline.
This calculation can be used for splines designed under the standard ANSI B92.2M or ISO4561.
This tool is defined for giving you directions and not definitive or complete designs. For that particular purpose, It is reccomended to run more accurate analysis and of course validate your designs with physical parts.

    Involute Spline Torque Calculation

Aditional Information about Splines:

• The function of a spline can be defined as fixed or sliding. Sliding one is oftenly used in synchronizers, shift gears and other similar machine elements.Fixed ones, are designed for not allowing any axial movement, therefore a minimun clearance, side or outer diameter is desired.A good practice on fixed splines is te use of pilot diameters for centering the load distribution and avoid excesive tilting in the connection.
• Splines work better when it is lubricated. Grease or oil will avoid premature failures due to fretting.
• Fillet root splines resist better the torque load, even when the minimun diameter is smaller compared with a flat root spline.
• A minimun taper angle on the outside diameter of the spline, along the overall effective length could help when torque twist the shaft and the contact distribution runs to the front or rear area of the spline. FEA analysis can help yo to determine the amount of taper needed.
• Splines failures would happen due to:
• Wearing of the spline teeth due to high contact stress and poor lube.
• Broken shaft due to high torsional stress.
• Spline fretting due to vibration, axial movement and poor lube
• Bending failure due to a small section under the tooth. Hollow diameter to big.
• If Faiure happen due to shear stress, shock load may be the reason.
• As general rule, use quality 6, according ANSI B92.2, for general purposes splines. Quality 7 allows more geometrical deviations and can be used for low spec requirements or when the safety factors are really high. Quality 4 and 5 are choosen when the spline is grinded and the contact distribution must be controlled.
• If the teeth number is low, you will require the tooth to tooth spline locatin to have more  accuracy to asure that all teeth share a similar torque level. It is more easy for a spline with smaller module and high teeth number to share equally the load.
• It is reccomended not to have parts in contact with a different in hardness > 8.
• Splines and Shaft materials:
• SAE 1010 & SAE 1020  Low cost material, under low solicitations and where part of the shaft is heat treated (carburized)
• SAE 1045  Common steel used for shafts. Low cost material. Can be heat treated and provide high load resistance. It is not a good selection if the fatigue strength is a mayor requirement on your design.
• SAE 4340 Cr-Ni Steel, bonified (Quenched and Tempered) high toughness and tension resistance.
• SAE 4140 Cr-Mo Steel that is commonly bonified and induction hardened. This steel is used for applications under high load requirements.
• Shaft Design (Link).
• Failure modes (link)
• Load Distribution (Link)