Use a good sharp 8" Chef knife or a cleaver and the cartalidge cut is easy. Use your hands and bend the cartlidge back and forth, feel along the bones till you find the point where the bone ends and the carlidge starts (right where it bends). Cut right along the base of the bones and you are done
Yes that is big piece of meat you cut of, but here is the good point. Rub the trimmed off piece and smoke it with the ribs. The trimmings will be done about 3 hrs. into the smoke and I usually use about 1/4 of them to make some sandwiches and/or cook snacks. The rest either get cut up and used in baked beans, or pulled, vacuum packed, and frozen for use in various other meals.