I know this ? Has been asked before so you may want to search the threads to read some of the other answers.
I'm new to the board but I've been making a few pens over the years. I use 3 or 4 layers / folds of aluminum foil. Works very well and I glue it in with 2-part 5-minute epoxy. The nice thing is you can layer it up as thick as you want it. No need to sand or buff and it looks good. I use pressure while it sets up (in a clamp) but once it's dry, it's easy to work with. Give it a try.