So once I get enough practice with fillet brazing (and it is going much better, by the way, thank you to those who offered advice/links) I would like to use that skill to build my own lugs. My questions is, where does one find the right tubing, that is, tubing with the right ID and wall thickness?

I know about and have used Aircraft Spruce for straight gauge 4130, but their approach is OD and wall thickness, so there's no consistency in wall thickness between the tubes I'd use for a 28.6mm lug, 31.8mm lug, and a 36mm lug. Is that just the way life is and it's up to me to file/sand down the lug to uniform thickness?

Thanks for the input!

The general rule of thumb is to use 1/8" size up with a .058 wall thickness from the tube you're trying to sleeve. For example if you are making a seat lug with a 28.6 seat and top tube you need to buy a .058 walled 1 1/4" tube to slip over the tubes. .058 is prety thick so it takes some work to get them closer to the acceptable lug dimensions roughly 1mm in thickness. If you have access to a lathe that can greatly reduce time spent on sanding buy turning down the O.D. of the tube.

there's probably some way to thin the tubes without a lathe, but it's a lot of material to remove. I've brazed .058 full thickness, it's really thick

I should clarify that I don't have a lathe and often don't have access to one, so usually I use my dynafile to bring the tubes O.D. down to size. That seems to work much faster than a file and I can keep the tube rotating to maintain pretty consistent thickness around the tube. Unterhausen is right about it being really thick, I would suggest thinning before brazing.

I do have a lathe and was planning to make a set of plugs to go into the tube ends for turning them down. One plug will be to prevent my four jaw from crushing the tube and one to allow a live center in the other end.

I should take a step back and say I got on Aircraft Spruce and wound up buying tubing that will roughly come out to what you guys are describing. It's got a .065" wall which I just kind of figured would need to be turned down as well as opened up a little bit.

Thanks for the input, guys!

Reaming is probably better even with a lathe. OD reduction is lathe work (or grinding as was mentioned).

I don't really know if 4130 is the right stuff. Most/a lot of lugs are just plain steels. There may be advantages to that, for instance the whole don't braze 4130 think is something we have nailed with tubes, but not so sure tiny elements are there. There are also other processes, like stretching and shrinking that might go better with regular steel. I know people use 4130, and getting the raw stock in the same draws in hi tens doesn't save any money... At least around here.

Then making lugs out of flat stock would be interesting, and possibly better, or more authentic looking. Cast lugs are just another way lugs make us do bad things.