The inner surface is that rough, you need to smooth it out?
Not knowing exactly what the state of the inner surface is, here's one idea. I might be inclined to make a square block of a suitably snug-push fit in the tubing and push it through to see if that would iron out the imperfections.
Try to make a living, not a killing. -- Utah Phillips
Don't believe everything you know. -- Bumper sticker
Everybody is ignorant, only on different subjects. -- Will Rogers
Law of Logical Argument - Anything is possible if you don't know what you are talking about.