I've got a small piece of walnut (about 1/2 x 3/4 in cross section) that I'd like to round over. Something about a 1/4 in radius. I've got a hollow with that radius, but I've never run across any uses of them going across the grain. My experience also suggests using a block plane isn't a good approach either. I'm thinking using a file is the way to go. Other thoughts.