It does sound like you don't have it tightened down enough. When I tighten mine down, I usually am holding near the end of the prop in one hand, and a screwdriver handle about the same length in the other, and I give it a good hard squeeze. (I keep pliers in the field box to get props off when both blades are broken, since with out the leverage, they will never come off). I also ususlly use a few layers of paper towl or something to keep the prop from cutting in to my hand. Though I do it bare-handed in a pinch. It doesn't atually break skin, but it does hurt a bit.