But the funny thing is it happened on 2 pens made from walnut made the same dayI have had this happen to me a few times. I think for me it happened during the pressing together from separate causes. If after finishing you dont re-square the ends the CA will sit proud of the end of the pen. When you press the pen the hardware puts pressure on the finish itself before the wood or the brass.....crack...you're done. Or I have had this happen from parts being slightly misaligned during assembly.