Victor3, That would be a bad one to make into a cannon barrel, but without special equipment and processes, the cannon tube maker has few options with which to discover such material defects. One way you can detect inclusions or cracks is to polish your tube to a finer degree than what's really necessary for use. I have seen cracks in only 6 of the thousands of steel and aluminum parts that I have inspected over 30 years. The Dye-penetrant depts. picked up on quite a few more when they inspected critical function hardware in the aerospace and aircraft plants where I worked. Only one, a 2.5 inch 1026 steel round could have been used for a cannon tube.
Inclusions can also ruin or weaken an otherwise good piece of material. As far as inclusions go, not too many people can top Mike's experience with a large inclusion in a 6061-T6 aluminum tooling plate which was being machined into a support fixture. He was waiting to inspect it's thickness as a 10 inch dia., 12 carbide insert tooth face mill was singing over the surface, removing a quarter of an inch as it went. Suddenly, a machinegun sound replaced the normal humming of the Big Mill. Everyone nearby dove for the floor!...and the machinist finally found the emergency OFF SWITCH. On the Millicron's table was a fine finish on the tooling plate, up to a barely visible, 1/2" circle, and a nasty finish beyond. After prodding the circle a bit, one-half of a hardened ball bearing popped out! Every carbide tooth on the face mill was shattered and coffee was leaking out of a styrofoam cup on a roll-away about 20 feet away!
Mike and Tracy
