Have cracked a frame twice. My first bike was an 18" wheel BSA. Great bike but after a few years the top tube broke just in front of the seat tube. My father found someone who was able to braze it back together and it lasted long enough that my brother and young cousin were both able to ride it. The other was my Commencal Super 4 which cracked at the junction between the top tube and seat tube. This was a common failure for the early versions of this frame along with the chain stay which I also broke