I realize this is an old thread, but the idea of turning a pen with cross-grain is intriguing. The marblewood example really stands out among wooden pens.
I suspect that most techniques and glue choices don’t actually provide full coverage between the tubes and the wood. The glue only needs to be strong enough to hold the brass tube in place. And because we almost always use lengthwise grain orientation, the wood will hold itself together well enough that the lack of coverage is not an issue.
In the case of a cross grained pen, I can see why full coverage would be important. I also suspect that the viscosity of the glue matters quite a bit as far as coverage. Most of the quick epoxies are rather thick, and it may be that TB II is a better balance and therefore provides more complete contact with the fibers. As far as adhering to the brass tube, there isn’t a lot of force pulling it out, so TB II is probably fine.
The biggest problem I can imagine in this scenario is adjusting the turning technique and tools to the grain orientation. To properly cut downhill, spindle turning techniques may end up with pieces splitting.
-- Barry, http://BarrysWorkshop.com/
