I created one not long ago whereby I drew each size keyway for each shaft diameter increment. I created a series of subtract extrusions and then used the suppress feature of the ipart to suppress all but the relevant extrusion. It worked ok.
I tried a similar method to create an intelligent iFeature for keyways but it did not work as intended. So i stick to the design accelerator keyways for most.
So you could try something like that if it helps?
Regards
Stew
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Stew, AICP
Inventor Professional 2013, Autodesk Simulation Multiphysics 2013
Windows 7 x64 Core i7 32GB Ram FX2000