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Keyways Index

Table showing keyway / spline design factor Kd

Coupling Design Design Factor Kd
Fixed (close fit) loaded
No relative axial/radial movement of the hub and the shaft occurs.; the relative positions of the shaft and hub are fixed using a suitable bearing or constructional design e.g press-fit , Shaft nuts.
Flexible/Sliding - Unloaded
Relative positions of the shaft and hub are not fixed; Axial movements of the hub along the shaft occur only when coupling is unloaded. The shaft is effectively fixed when loaded.
Flexible/Sliding loaded
Sliding coupling with loading:relative positions of the shaft and hub are not fixed; axial shifts of the hub along the shaft occur in loaded couplings.

Table showing spline application factors Ka

Power Source Type of Load
Generators, Fans
Light shock
Oscillating pumps
Intermittent Shock
heavy shock
Presses, Shears
Application Factor (Ka
Uniform (Turbine, Motor) 1,0 1,2 1,5 1,8
light shock, (Hydraulic Motor) 1,2 1,3 1,8 2,1
Medium shock, (Internal combustion engine 2,00 2,2 2,4 2,8

Table showing splines distribution factors Km

This factor relates to reduction in strength as a result of misalignment of the spline

Misalignment (mm/mm Load misalignment factor (Km )
12mm face width 25mm face width 50mm face width100mm face width
0,001 1,0 1,0 1 1,5
0,002 1,0 1,0 1,5 2,0
0,004 1,0 1,5 2,0 2,5
0,008 1,5 2,0 2,5 3,0

Table showing fatigue life factors for splines Kf

No of torque cycles
(stop/start cycles)
Fatigue life factor (Kf )
Unidirectional Fully reversed
1 0001,81,8
10 0001,01,0
100 0000,50,4
1 000 0000,40,3
10 000 0000,30,2

Table showing wear life factors for splines Kw

No revolutions of spline Life wear factor (Kf )
10 0004,0
100 0002,8
1 000 0002,0
10 000 0001,4
100 000 0001,0
1000 000 0000,7
10 000 000 0000,5

Table showing Typical design strengths for selected materials

Material Hardness Ultimate
Tensile Strength
Compressive Strength
Shear Strength
BrinellRockwell C MPaMPaMPa
Structural Steel150-200- 35090140
Carbon Steel220-270- 500130200
Alloy Steel300-35033-38 600200275
Surface Hardened Steel65045-53 650250275
Cast Iron
(Speroidal Graphite
400- 400135140

Sites Providing Relevant Information
  1. Mitcalc.com...Excel based programme allowing detailed design of shaft connection (19 Eur)
  2. Zakgear-Spline Stress Calculation... Calculator and associated equations of tables - Extemely useful - US units (not metric)
  3. Wikipedia _Spline Calcs in English Units... Extensive notes similar to Zakgear US units -not english
  4. Tasman industires...Supplier of keys
  5. Bonut Engineering...supplier of keys
  6. Technifast Ltd...Supplier of fasteners and keys.

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Keyways Index

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Last Updated 19/01/2013