Doug, these look fantastic. Raphael did well.

For bilaminate "lugs" (just a sleeve, really) is there an economical way to find stock? Cutting up lugs doesn't seem efficient; turning down thicker tube stock seems tedious. But maybe the latter is the way to go?

I had misunderstood pre plugs before; without the bevel what would stop about half of the brazing material from melting into the insid of the plug instead of between the plug and tube? Does the capillary action draw most of it into the gap that effectively? Will there always be some brazing material that falls inside the plug? The bevel seems essential rather than a nice addition.

This has rabbit-trailed off, but it's my thread anyway and it's still an incredibly educational rabbit trail for me. So thanks for all who have contributed.

Claude Butler is a UK brand of bicycle frames that used bilaminate construction after the war because of the lack of availability of lugs. When their frames are painted, it is hard/impossible to tell they didn't use real lugs.

Wicks Aircraft and Aircraft Spruce are 2 suppliers of tubing suitable to make bilaminate sleeves. Tubing with 0,058" walls is what is most available. Usually that thickness is reduced to at least .40" so it doesn't look thick. Using a lathe is the easiest method but hand filing is possible and doesn't take forever.

Yeah the height of the shoreline will be ~.062" if you use .058 for the "lug". The difference being the clearance between the two tubes, which will hopefully be filled with braze. 60 thou is OK for brazing practice, but looks terrible on a bike to ride and will probably result in shorter fatigue endurance. Large sudden changes in section thickness cause stress-risers, where fatigue cracks will start. So your lug should be thin compared to the tube wall. 40 thou would be OK but 30 would be better.

If you are lacking a lathe, you'll want to file the "lug" down either before or after brazing. I prefer before, because the brazing will go a little quicker, and there's no chance of accidentally thinning the tube that way. But there might be practical reasons to file it after. Or a combo, some before and some after.

If you just want to see how much penetration you got, on a testing sample, leaving it full-thick is OK. But then when you braze a real lug you may be surprised by how much faster the lug heats up.

Somewhere in some far corner of a warehouse google won't help you find and the person that answers the phone doesn't remember they still have in stock, is tubing with an OD of 1 1/16", 1 3/16" and 1 5/16" with a wall thickness of 0.028" (actually I have some of that). This tubing can be used to form bilaminate fake lugs that won't require thinning.

https://cimg5.ibsrv.net/gimg/bikefor...0c51b8a4ba.jpg
This bilaminate lug I made using tubing that had a wall thickness of 0.028".