I found that a sweeper is not strong enough to work on walnuts. Maybe mine was just too weak, and others have found differently.
I drive on them to knock the soft husk off and pick the nuts out the next day. I put them in a 5 gal plastic pail, and wash them with a stream of water, tumbling them around until the water is clear. Then lay them out on newspaper to dry (inside if the squirrels are around /forums/images/graemlins/wink.gif ).
After drying, they store pretty well. I crack them in a 4" vise and find that offers good control. However, using a hammer on a solid steel surface like an anvil works good too. My grandmother cracked hickory nuts and walnuts until she was 95 years old.
Using rubber gloves will keep the stain off your fingers. /forums/images/graemlins/wink.gif