Originally Posted by
estebe
Unfortunately i don't have access to a lathe but how hard could it be to fabricate a cyclinder to the inner diameter of the tube? Then drill it in the middle, tie a piece of steing to it and pull it out? It's really close to the bottom bracket so i think in theory it would work? Or?
You got the basics, but how do you get the expander plug up in there, much less pull it out without damaging anything else. Some of which has been mentioned by others, like the the brazed parts of the tube ends where it's lugged.
Also, this dent isn't something just ready to pop out. The metal was re-shaped and will have to be re-shaped if you swage it with your plug. And typically that requires going a little more in the other direction which has you bulging the tube all the way.
Also, inside diameters on tubes used for bikes isn't always the same through the length of the tube. I think the ends are narrower diameter than the middles. Don't know where this changes or if it is unique to double butted tubes or what.