They just rust out (warp too) and grind. Actually I should correct that: one of the 3 times, two front ones were only turned (ground/renewed), but twice were complete replacements. The second replacement I managed to get the rotors warrantied, as it was just under a year. (During that year, I only put 7500 miles on the car.)
WHERE ARE THE ROTORS COMMING FROM? WHAT PARTS STORE? FOR INSTANCE I HAVE A CHEVY. BLAZER WITH OVER 100 K MILES AND ONLY MACHINED ROTORS ONCE. DOES THE REPAIR SHOP SAY WHY YOU ARE HAVING THIS MUCH TROYBLE?