Another (albeit backyard) method I have used is to put the tinyest tackweld on the bolt to the plate, undo the nut then grind it down smooth again to remove the bolt.
Sorry to resurrect an old thread (but it's got great info in it) but I went through every trick in this thread short of using an angle grinder to cut the nut in half.
Were the blades on a 550 Pro, the previous owner had put them on without any lube, allowed to rust and absolutely HAMMERED them on with a rattle gun and then allowed to rust for a while to boot. And of course they were the old style blades, which don't have the hex hole on the backside, seriously who was the sadist who designed those?????? Ghastly design that makes zero sense and surely after undoing once they'd see the obvious design enhancement options!
Anyway I was just about to cut the nuts off and figured I'd give the spotwelds a quick go - as if cut off the bolts and nuts would be fubar anyway. Took a couple of tries on a few but managed to get them all off, though the thread on a few of the bolts likely was nearly ruined.
Definitely great info in some of these old threads, plenty of stuff on the net about removing the new blades if stuck but nothing at all on the old ones and those are the real buggers.
