I only deal with black walnuts on the small scale, so most of the work is done by hand, or foot in the case of "hulling" the whole thing. I've found that my shoe can do a quicker job of getting the green hull off with a quick back and forth roll, once the covering starts to loosen anyway. Then after curing, I remove the flavorful kernels with a hammer and anvil. Sounds tedious and time consuming and it is... but it's the best way I've found to get them out without crushing and picking through the pieces and biting down on the occasional, incredibly hard, shell piece. A nut pick is quite handy as well, a little practice and you'll get out enough for a snack in minutes. The shell and nut thickness can differ from tree to tree (my favorite 2 trees are loaded this year). Start with the pointy end up if you're going the old fashioned route at cracking like I do, it tends to separate the halves and quarters, rather than crush, just go easy with the hammer.