A friend is very excited about harvesting black walnuts this year, having heard great things about their health benefits. There's the small matter of reaching the meat, however, well guarded by the green hull and the extremely hard shell.
One technique for removing the hulls is to drive over them with a car. Traffic along Harrison Street was being very cooperative in this regard, but I was a little leery of collecting nuts so close to a busy road.
If you're moved to give black walnut harvesting a try, here's one of many links with instructions.
Most walnuts go begging, like these on the lawn at Brearley House. That leaves an abundance for those willing to give harvesting a try. Best to be armed with a good nutcracker. Below are the results of my research.
Smaller nutcrackers like the Reed get high marks for everything but black walnuts, so you'll need something larger and stronger.
Here's a recommendation from a friend: "I have a Gardner nut cracker which I am very happy with… I think the cost is around $80 and it works very well with thick-shelled nuts like black walnut, butternut, and hickories and hicans. (I am also told there is a Chinese knockoff to be avoided.)" He also mentioned a Kenkel model.
There's also a Hunt nutcracker that came up in an internet search.