hey guys, just a heads-up for you, in case you might be interested:
I've started a collection of
TUBING SIZE CHARTS from the various
TUBING MANUFACTURERS on facebook, to help people who deal with vintage bikes.
I don't know how to direct-link the post itself, but here is a link to the album that's part of the post:
FB Tubing Charts Gallery on FB
You'll find outside diameter listed, as well as the wall-thicknesses. Finding out the seatpost size is a simple mathematical operation (OutsideDiameter - (2*WallThickness)), and for single-butted tubing, it would be by subtracting the non-butted section's thickness.
As someone mentioned, I am skeptical that builders went through the trouble of "reaming out" seat tubes to merely increase the diameter, since, seatposts were available in all diameters needed for the various seat tube sizes. Polishing/refinishing however, is a different matter. (and then there is the matter of doing it for the wrong reasons: because you don't stock the correct size seatpost).
This may have been necessary for seam-welded tubing, that wasn't finished on the inside by the tubing manufacturer (and thus needed to have the weld-seam removed), or cheaper "gaspipe" tubing. But it was not needed for quality tubing.
I've seen mentions that reaming was necessary from distortion after welding... but for the most part, in these forums, we are usually talking about better quality bikes made from better alloy tubing, which required brazing, so as not to overheat the tubing.
If any reaming was needed to correct significant deformation from welding, then it would either have been over-heated in the first place or made from very low-grade tubing that is thick enough to allow for such temperatures and more leisurely manufacturing methods.
Some seat tubes were double-butted, while others just used more economical thicker straight-gauge tubing. However, some bikes (like an old Peugeot that I once had) seemed to use smaller outside diameter tubing as well. But most seat tubes were single-butted, with the thicker butted end at the bottom-bracket shell, and the larger-opening straight-gauge end at the seat-cluster.