when I first started deep hollowing,I made a shaft out of 1/2" bar sliced halfway through lengthways at the end with a large teardrop cutter at the end,was making 12" deep vases at the time in well seasoned wood,cracked a few pices of wood,shattered a few pieces,never broke the shaft though,but looking at the shaft on the crown tool it isn`t very thich by the look of it,even so,you would have to get a hell of a digin to break it.