Emmett Manley, Lakeland, TN
Thanks to everyone for some great input and food for thought. I am not having any particular chucking problems; rather, I just wondered if I was overlooking something important. Really, most of my concern about wood coming off the lathe occurs during the phase when asymmetrical wood is between centers and before the much more secure tenon-held-by-scroll-jaw stage.

Relative to tenon size, my operating rule of thumb has been: big pieces of wood, use the largest tenon feasible, even if the jaws are near maximal expansion; smaller pieces of wood, use a tenon size just a little larger than the minimal jaw diameter. I have reached this happy state largely via intuition plus some trial and error.

I am pleased to learn that, except for the knuckle busting hazard, I don't have to be concerned about fully expanding the jaws. Also, I had not considered the influence of grain direction, but that certainly makes sense and fits my experience.