I am aware of steel and stainless steel lugs. Can/are other materials sometimes used?

I think I have seen video of casting magnesium lugs for experimental magnesium bike, and one instructable where ABS 3d printed lugs are used for carbon bike.

Could brass be used?

Can 3d printed stainless steel be brazed?

Some other material?

I am guessing that the 3d printed metals can be brazed, but I would worry about fatigue. Brass is pretty weak, especially in fatigue, so the section would have to be thick. If you admit bonding processes, lots of materials could be used, but I don't know why you would bother. The ABS lugs with carbon must have just been for holding shape?

yes, ABS lugs were for holding the shape and covered and wrapped around with carbon.

You say that Brass is weak, is that Yield strength of material that is important? Brass seems to be 200MPa and steel 450-600.

I am afraid my English is not up to the task, I did not understand what you were referring to with: "If you admit bonding processes"?

As for reason for asking, I am just curios if there are viable options to make custom unique lugs. Since steel is very difficult to cast in garage, I wondered if some other material might be an option.

Tom Kellogg (and probably others) makes his own custom fillet brazed lugs. There is a tutorial under resources on the Framebuilders Collective site. Looks like unlimited angles and personalization possible.

Nice tutorial, thanks!

With steel tubes and brazing lugs are more to locate tubes and spread joint stresses then to be the strength of the joint. I have always thought that one could trim back the socket depth of a lug to 4mm's (or so) and not loose any joint strength (as long as the miters were done well). It's been said that most all lugs are overkill as far as strength goes. It's been said many times by builders far more experienced then i that the joint's integrity comes from the miter, tube to tube contact. Given this any material that is brazeable could make a lug and be OK. Enough of the material would be needed to equal the strength of a steel lug I would think.

I have joked that one could make a frame from Styrofoam and chewing gum, if enough was used. Andy.

I hear that a lot also, but what I don't get (and I don't do lugs for the most part) is what the heck they are talking about. Don't most tubes normally just penetrate the lug and get trimmed "roughly" off. With the exception of the top tube to seat tube. You can have head tube lugs that meet the head tube at a tube, though some simply penetrate the tube also, but you still have four other joints that are just pass throughs.

Now if you want to see tight mitres the TIG guys will make your day, they tend to use machinery and cut to very tight tolerances, though any builder can do that whether it helps or not.

MassiveD- You're asking the wrong person but I'll give you my understanding.

There are a few issues going on here. One is joint stability/alignment during brazing. It has been said by many that the better your miters are the less the after brazing alignment issues will be. The joint will tent to shift and if the miters are tight and consistent there will be no space for shifting to occur.

BITD of pressed lugs there was a large area of void just at the miter. So to insure the joint of max strength the filler would need to fill the void (and if you're using Silver we all know how it doesn't like this) OR to have the tubes touch and the filler flow between them.

Are the lugs designed to transfer the stresses of use through only them? If so then the tubes being cut to only enter the socket (and not butt against the joining tube) will be ok. I don't see this assumption being stated or suggested in any current lug manufactures info, suppliers listing, or any builder's processes. Granted this design might be the actual goal, but if so some one is doing a poor job of letting the building world know this. The exception to this is the use of a one piece head tube/lug socket that some high volume manufacturers used 20+ years ago. I think it's easy to say that the small builders were never intended to be in the loop as far as the engineering of this frame part goes.

Yes, there are possible millions of frames with poorly mitered, even square cut, tube joints out there. That the brazing and lug's strengths are good enough to handle this construction method is not a guaranty of absolute effectiveness. Just that the results meet the cost to produce VS warranty costs that each company sets for them selves.

I am not a good enough builder to say that my miters are "water tight" as some claim theirs to be. I have some faith in the strength of both lugs and fillets to fully handle the stresses of use. But i do strive for better fit up and miters and feel that this makes for a better bike. Whether you'll ever test out this betterness is not my concern. When you produce many frames that work you do tend to come to some conclusions about processes and their benefits. When you repair mass produced frames and see their failure modes you come to other conclusions. In the end you find there are many ways to skin the frame, some are more to your liking then others. Andy.

So is than filler also supposed to find its way into the miter between tubes, not just between lug and tubes? (if brazing is done properly that is)? (sorry if this is rookie question)

Yes. Modern investment cast lugs with theit greater contact surface (and virtually no internal voids at the miter) make this much more likely to happen. Andy.

The strength of a lugged joint comes from it's surface area. Having the butted mitre maximizes that area and also allows for an internal fillet.

But I wouldn't be surprised if that is overkill. The pierced BB is well triangulated I guess so that it works. I built a frame with a one-piece headtube and it seems fine as well. In that case the sockets are pretty thick (heavier) since they are structural.

All; FWIW; My process is to put the finished mitered tube back in the jig, and clamp it with the tube blocks, and then put a small Mag-lite in the other open end of the tube. I keep the mag-lite on a hook right next to the on/off switch for the lights which I designed in as one of the 4-way switches for the shop and located it on the column right next to the build table. The less light sneaking out at the joint, visible in the now darkened room, the better. If it looks good (just a "UFO glow", I turn the room lights back or and move to mitering the next joint. I want all the joints to be very well mitered and inspected before adding the lugs to the equation; if I am using lugs for that build. /k

Seems to me that most of the luminaries these days are supporters of pining, which may or not benefit from this as you say. I still come down to the fact that the majority of joints have no interface, compared to Tig where they all may (not that that is relevant to whatever is happening in lugs, just interesting). A TIG frame could have something like 11 miters, where the lugged would be say 4 or more.

I just think it is yet another thing the lugmasters say without really thinking over whether it is actually happening or not. More pixie dust.

I do appreciate people rising to the challenge on this, and putting out some interesting answers. I take it all seriously, I am just in skeptic mode for the sake of the argument.

mitering certainly has a bigger effect on alignment of tig or fillet brazed frames, but is also important for lugged frames. I'm fixing a frame right now that had some mitering issues and also had very thinned out lugs, so when the builder also made the vent holes way too large, there wasn't enough margin to keep things from failing in fatigue. Badly mitered frames were a thing you can find on production bikes, not reputable builders. Some of those badly mitered production bikes aren't really thought of as production bikes by many, but those companies are pretty much gone now.

Another segment of "as the thread drifts"- MassiveD seems to question the need for tube to tube miters with lugged frames. To a degree i agree, and have said so. But what one can get away with and what one does has a range in real life. I have always felt that tube contacts are better, and it's this betterness that i aim for. Sure i could save much time just square cutting tubes and not getting their mitered length just so but then some of the reason to do this building thing would also be gone. I've seen enough frames (mostly production but also a couple hand built) that have had virtually no filler penetration in to the lug sockets, let alone reaching the tube contacts if they existed. These frames lasted for thousands of miles, many years. BUT the reason i can describe them is that they ultimately did fail.

An interesting story i was told years ago was when Eisentraut visited some Ital. brands' factories. At one (famous for it's orange paint) he saw a HT/TT/DT brazing station where the entire section was bright orange, well up the DT and TT. He, of course, was a proponent of Silver brazing and using as little heat as possible. Yet here was this revered brand doing the opposite. This brand had a very good rep for it's durability and integrity. So what gives? Al figured out that the evenness of the heat and the very full penetration of filler (that this high and even heat allows for) meant that there was little distortion, warping and good tube to tube internal fillet.

Eric- You mention a vent hole too large. Do you have a opinion as to what's too large? Andy.

I only use 1/4" vent holes. I've seen people say anything larger than 3/8" is asking for trouble. The broken frame I'm working on had holes that were 3/4" or so. Fortunately, there was very little meat on the lugs so the crack just went through the head tube directly to the lug shoreline, skipping the lug itself. The shoreline was gone, there was one tiny connection between that part of the head lug and the head tube.