Originally Posted by
cyccommute
While people may have the skills necessary, they don’t have X-ray vision. Most people going for this kind of repair may not tell the welder about the thinness of the steel tubing. The bicycle owner may not know or know that it’s important.
In some cases, not all, there are holes that allow you to see wall thicknesses. These holes are used to for pressure equalization when welding. If you cap off both ends of a tube or pipe, when you go to weld the last cap the pressure change between inside the pipe/tube and outside will deform the weld bead/pool. I did exactly this a couple weeks ago - capped off tubes. They were real small (3/8" OD, around 1/4" ID) and I "spot welded" around the tubes to build up the material to close the ends. The weld pushed out - I assume from the hot tube causing the air inside to heat up and expand as I welded = higher pressure inside than outside until the part cooled.
In any event, holes in parts will alleviate the pressure differential. So if there are holes in the tubes, especially - you can find the wall thickness from that hole.
On my Disk Trucker I noticed the rear dropouts had holes that opened up inside the stays. This wouldn't give you the stay tube thickness, as the hole is in the dropout, but is an example of such a hole existing.