I haven't read all of the replies here so if this a double I apologize. I've worked with walnut a limited amount with no issues. However, it should be mentioned that black walnut is a toxic plant. When working with it you should be careful to make sure shavings & sawdust are contained as it can be lethal to certain animals & other plants. I first heard of this when working in the driveway of my old house. When my elderly neighbour noticed I was working with black walnut he cautioned me. From what I can find online it's not as bad as he made it out to be, but he likely had some first hand experiences to draw from. Either way, better to be cautious.