Diyfixman,

I don't think the speed was too fast for routing, just too fast for your under spec'd connection with a too heavy lump of non-concentrically turning metal. Tiny, short shaft, loosely fitting sleeve, held on by set screws. Couldn't expect that to resist all the forces trying to tear it apart. Because of the length of your chuck and bit combination, the effect of the first little bits of deflection, due to imbalance and the load on the cutter, rapidly became magnified and ran away. Lee