I am not sure if this is appropriate for the frame builder forum, but I think it is somewhat relevant. Please let know if I am in the wrong forum and I will remove this thread. Thanks.
I recently purchased a 3rensho frame in decent condition. As I started handing components on the frame, I noticed that the middle section of the top tube seemed to be sagging a little bit. I put a straight edge on the top tube, and, sure enough, the middle of the top tube was about 2 mm lower than the end points of the top tube. It was essentially a very gradual and gentle curve in the top tube. The frame seemed otherwise straight with no sign of being previously crashed. Since it is a petite frame, I was even thinking that the original builder was trying to create a lower standover height this way. On the other hand, 2 mm contributes nothing to standover height for all intents and purposes.
My questions is: Is this something that I need to worry about? If it is, is there a simple way to fix this other than a complete tube replacement. Thanks a lot for you insight.