Planers seem to uniformly have bolts super tight. I remember changing blades on an old Ryobi 13" and my DeWalt 735 and having trouble. In this instance percussion is your friend. A 12 volt or larger impact gun will help get the bolts loose. just be sure you are using really good bits that fit very tightly in the screw heads. I bought a nice set of bits for this specifically and all the bolts came out without stripping.