My therory about tangential grain shavings from a razor sharp plane is not working. the oblique grain just bust off into small shavings nothing long enough for your pupose. Do you have some exta walnut that you couild cut a section with the grain orintation such that you could glue in a fitted chunk and having let it dry a day or so shave off the bulk and reinlet the lock to tolerance in that area? If not I can send you a chunk of Black Walnut to make a patch from if you pick up the shipping. A flat rate priority box runs 11.00
