I *could* blame it on operator error, but I cut 5/8" instead of 3". 5/8" is the maximum possible depth for this bit. After 2" the bit broke right off the tip of the thin section. (ALWAYS WEAR GOGGLES!) It was hot as hell when I pulled the cutting part out. Hurry so don't be afraid to make a deep cut. Slow down. And wear safety goggles!