I haven't tried a CK wedge collet for this although I have one on the TIG. It works for welding as there is no force on the electrode when the arc is going. Having tried pin vices with their pinch type holding and finding that they slip, I think for grinding the CK collets would do something similar, as in reality they are only holding in one place, so the tungsten can flop around a little. For me, this size ER is great as I can tighten it by hand with this setup enough that it does not slip and the compression nature of the collet means it is stable side to side.

Michael