Hi and welcome,
It sounds to me if you are being a little too quick in turning and not allowing the glue to harden/cure. There is a lot of pressure placed on the glue between the blank and tube when turning.
I use Alaldite two part epoxy which (up until now) has served me well: but I always wait for at least 12 hours before I turn. I know the temptation is always there to get it on the lathe, but patience
is a wonderful asset and pays dividends in the end ( Oh dear, now I have gone and said it :pray:)
I do not use pen end mills either; just don't like them. I find that they always need sharpening or cleaning. A disc sander correctly set up I find is better for me.
I am no expert compared with some members on here, but this is just what I have discovered after making litterally hundreds of pens.
Hope it works out for you.
Cheers,
Frederick
Phil, any chance of spell checker on here; my spelling is awful 