The lawn mower began emitting horrible crashes, which turned out to be coming from a flange at the rear of the mower housing that was formerly spot-welded to the main chassis. Those welds broke and the flange occasionally vibrated into contact with the blade, causing heartache and confusion for both parties.
Re-spot-welding the flange wasn’t in the cards, but the elaborately formed piece of steel did have a flat section in contact with another part of the chassis with just enough meat for a bolt. I grabbed the two with a Vise-grip, whacked the flange until it was more-or-less lined up where it should be, drilled a hole, and popped in a 1/4-20 bolt:
The curved section of the flange faces the blade, with the vertical end pointed anti-spinward: the blade nicks that edge.
A dab of red Loctite and a nylock nut topped it off:
Then I could complete the mission…