I've turned well over a hundred pens since I got into woodturning in 2020. I've used various kinds of CA glue, the gorilla glue (the foaming stuff), and various kinds of epoxy.
In the end, I settled on T88 System 3 epoxy. This stuff seems to give me the best bond, with the fewest blowouts. I used JB Weld for a while, which is clear when mixed, and it does a good job, but its not quite as good as the T88 stuff. The T88 mixes yellowish, and it gives an extremely good bond. You can warm it up a bit for it to cure faster, if you need. This can reduce the sheer strength a bit, but it can greatly speed up cure time. Normally it will take a day to cure, at 70 degrees, but if you heat it up to over 100 degrees, it'll take a couple of hours. At max temp, 150 degrees, it'll fully cure in less than an hour, however there is a bigger hit to sheer strength.
I usually warm it a bit, so it cures in a few hours. I haven't had a blowout that was caused by the glue failing. I have had some, but they were due to wood failures, and the parts of the wood bonded to the glue, remained bonded, other parts of the wood (or resin) would break off or chip if there was a structural issue with the material.
The T88 resin, after a while, will start to crystalize. However you can easily restore it to its normal viscosity by boiling some water, letting it cool a bit, and putting the bottle of resin (not hardener) in the water until it returns to a fluid state. Once it does start to crystalize, it will eventually do it again and again. I don't know if it will eventually go bad, but so far it has not for me with this latest bottle. I'm about through it, so, I'll be getting a new bottle soon enough. A set of bottles will last through quite a few pens.
A thought on Gorilla Glue. Some pen turners like this because it fills all the space, and that was why I originally used it as well. That is certainly a benefit. However, I spend time over on the IAP forums as well, and segmented blank makers noted that GG could cause segmented blanks to break or unduly shift, ruining the blank. I eventually experienced that myself, even with a relatively basic segmented blank that was simply a core of one material, some metal layers separating other wood layers. The various layers twisted and the end layers separated, due to the foaming nature of GG. Even in the case of single-material blanks, I have occasionally run into the tube itself, shifting with the foaming action of the GG, and I had a couple cases where the tube shifted slightly outside the end of the blank. I ended up salvaging them a bit, by using some replacement tube and gluing it into the cleaned out other end of the blank, and sanding it down to the right size again, but...in the end, I stopped using GG because of this issue. The foaming action can be problematic.
Gorilla Glue makes a non-foaming glue as well. Its clear. It is not as hard as CA, maybe even slightly softer than epoxy. I am still experimenting with it, but it might be a viable option. In the end, I usually go for the T88...its just a superior epoxy with a superior bond, and I've never had a bond failure with it so far.
