I am going to try sharpening a blunt long sword and wondered what the preferred angle for the secondary bevel should be? I've heard anything from 17 degrees to 30 degrees. What was the typical edge angle on period swords, say 13th - 15th centuries? I want the sword to cut well, yet have enough strength to take the odd occasional clang on steel or wood, not edge to edge mind you, just the errant oops.