Hi guys, this is an older thread but it just helped me tremendously. I wanted to give a shoutout and thank you all for sharing.
I received some 3" fiberglass tubing for a new scratch build I am working on, and the ends were all a little jagged and slightly angled. It's my first time buying raw tubing outside of a kit so I'm assuming that's normal.
After reading through this thread and working with what I had on hand, I used sheets of 8.5x11 printer paper and masking tape to create perfectly square wrap-arounds. I then slid this up to within 1mm of the lowest valley. Using an orbital sander with 120 grit I took the high points down and flushed everything to the edge of the paper.
As a finishing touch, I ground connecting sections together with a coupler tube inside as mentioned by several folks here. That evened out the last 5% of variance left over from eyeballing the sanding. The result was fantastic.
As a side note, I used a chop saw with a metal cutting blade to size a couple of the pieces. That also worked out very well.
Thanks again!