Two things and neither of these may apply. Frist, when I started making pens, I didn't have any instructions other than the little sheet I got when I purchased the kits at Woodcraft. That sheet did not say anything about the wood or resin or whatever needing to be milled right to the tube. First pen I made, I guess I was lucky, second pen not. The wood cracked right at the nib as I was pressing the transmission in, it was a slimline so basically the same things as a 7mm euro. So, make sure the material is milled right to the tube. The second possibility is the size drill bit you used. Lots of people use a 7mm bit for these, others use a "J" bit and I use an "I" bit. You can also use an "H". The point is that if whatever drill bit you use leaves minimal clearance for the tube and you use CA or epoxy to glue the tubes in, the tube doesn't really have anywhere to go when you press the parts in. If you have a pretty tight fit which is usually the case with the Cross transmission, the tube has to expand and if it is already basically in contact with the material, the material will try to expand. You can't do that with resin, or antler, or and even some wood.