Nice pens, Terry. Much better than my first attempt, still used by my dear long-suffering wife. Will publish a pic if I get the chance.
Don't throw out tubes if the wood cracks, just turn the wood down until its so thin it breaks away from the tubes. Then use a skew in 'planing' mode to clean the glue and wood residue off the tubes. Then try again! I sometimes take three attempts for one reason or another (mostly related to my own stupidity) before finishing a pen.