Spline root failure

[MattW20]

I currently have a spline that is cracking in the root of the spline. According to calculations for shear stress and compressive stress the spline should not fail. Is there a way to calculate the stress at the root without using a FEA software?
Thank You

 

[Fabrico]

Maybe calculations for load are off.

 

[GregLocock]

Sure, any gear design reference will take you through it. Shigley probably does as well.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Pressed]

Hey

Matt here are some things to ponder:

[URL unfurl="true"]http://www.geartechnology.com/mag/gt-solid.htm[/URL]

[URL unfurl="true"]http://www.zakgear.com/External_Spline_IN.html[/URL]

[URL unfurl="true"]http://www.kisssoft.ch/english/manual/index.html[/URL]
[URL unfurl="true"]http://www.hexagon.de/wn4_e.htm[/URL]
[URL unfurl="true"]http://www.mitcalc.com/en/products.htm[/URL]
[URL unfurl="true"]http://home.swiftdsl.com.au/~gears/[/URL]

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[rob768]

did you check the level of torsional vibrations? Most likely it is fatigue due to some form of torsional resonance.

 

[clshore]

Fatigue cracks at the root of splines commonly occur due to localized bending at the surface discontinuity where the machined groove meets the surface of the shaft. These are typically rather sharp, even when the profile of the spline itself is not.
These can be minimized my 'necking' the transition area down to the base diameter of the spline, and tapering the transition back to the full shaft diameter.
Even is cases where there is not much room, a circular groove with width equal to the spline depth can help.

I had this issue with stub axles, added the groove, and eliminated it.

Carter Shore

 

[Tmoose]

Is the shaft hollow?