I had a TA crankset (or maybe a Lambert copy of a TA) whose chainring bolts wouldn't come off no matter what. I rarely go to bike shops, but I knew Larry would know what to do. He was my boss at my first job way back in 1978. He's a genius mechanic. He put the crankset on the anvil part of his vise and tapped on it gently with his ball peen hammer. He explained that it freed the threads from each other. I had not heard of that technique, and I haven't had to use it since.