[tadd]

Walt:
I have been accused of that by many good people... over designing too :-).

You make really good points. I actually hadn't considered the chains as a locating device, probably cause they aren't supposed (designed) to do that, despite doing just that.

I was just thinking a spring in the splined tube would be trivial to add, allow a bit of movement (as you pointed out), yet provide a resistance to gross movement.

I think my biggest concern was maintaining full tooth engagement... but like you said, the chains wont let it walk too much.

Thanks for the reply! More to think about...