Friend of mine brought some nice oak by to get it planed today. It was salvaged from old church pews and had a basic clear finish on it. (Varnish?) I thought the knives in my planer, DW235 were in pretty good shape as I hadn't used it a lot since they were new. Ran one board and said this won't do. Opened it up and turned them around to the fresh side. Ran a few more boards and they act like they are very dull already. Is the finish on the boards what is dulling them so soon? Could have bought new oak for the price of the blades!