I'm not exactly a pro, but I have carved approximately 10-15 lithos in the past few months. However, this weekend I had two break in the final few minutes of a three hour carve, both of the same picture. I don't have a clue what is happening. Each time the bit finishes the carve, but the top 3 or 4 inches breaks. Any ideas? I am using a 3/4" piece of mdf with an 8x10 recess in it as a sled. I wondered if somehow the end of the corian is rocking off the bed of the sled, but I haven't had that problem before, so I'm stumped. Pictures of the cracked lithos are attached. As you can see, the first carve has an unintended carve through near the upper center. Both breaks appear in the same approximate area, though the first fractured across the entire width, while the second took out the upper right corner, then the upper border. Both carvings are displayed 90 degrees from their position during the carve. The broken pieces are actually on the left end of the carves. Thanks for any advice. BTW, I did not use "bit optimization." Don't know if that might have helped. Also, I think the actual break occurred when the bit reached nearer the end than what appears on the carves. I checked the progress of the carve last night at about 97% and there was no problem.