Lug selection tips for beginners
 

When teaching someone new about lug brazing, are there certain shapes you would choose or avoid?

I'm asking this because I'm building in my mind the frame I would want to make if I take a framebuilding class. The frame I want to build, of course, has some features that are probably not in the cards for a beginner in a time-constrained class, things like bilaminate lugs, custom lugs filing, couplers, etc.

But I have my mind on a Cinelli SC fork crown, and I was curious if these would be easier or more difficult (or the same) than any other lugged crown:

https://cimg0.ibsrv.net/gimg/bikefor...7efb1fb100.png


For main lugs, while I am not set on these, I have wondered if windowed lugs would be easier (can see if the silver flows all the way through) or harder (less mass overheats easily):

https://cimg9.ibsrv.net/gimg/bikefor...6fc1ac2454.png

I think that the Cinelli SC type crown pictured would be a less than optimal choice for a first fork build - I’d suggest an external crown, not an internal one like this.

Regarding lugs, you should have practice-brazed at least six lugs or more before building a set of lugs into a frame. Do a proper miter, fit the lug, braze it up, then slice it in two with a hacksaw to see how your penetration looks inside. It would be educational, yes, to drill some holes in the lugs to watch the silver getting pulled from one tube to the next by capillary action, something simple like this is fine.

https://cimg9.ibsrv.net/gimg/bikefor...c75471116.jpeg


The lugs you’ve pictured look like some classic pressed lugs like Haden Royal Sovereign or Prugnats - which would be ok but probably rarer or more expensive than a basic set of investment cast lugs of current production. But it’s up to you, and I’d take the advice of the instructor in your framebuilding course to heart. I know that many of the students of Doug Fattic’s courses pull off some amazing looking builds. Enjoy the experience!

First- If you're taking a class I'd ask the teacher about what they think about your choices. We can give all sorts of opinions but it's the teacher that will be there with you.

Generally lugs that have simple shorelines and are of the angles your design needs will be the easiest to work with. The modern cast lugs tend to be much more nicely finished from the factory than the old pressed/bent/welded ones (like the Prugnat S4 pictured) but I seem to spend not too much less time filing/sanding cast lugs.

I do agree with practicing a few times before starting the actual frame. FYI a tube that is 1/8" larger in diameter than another tube, and also has a .058" wall, will slide over that second tube with about perfect clearance for flowing braze. Practice "lugs" can be had for real cheap by cutting simple sleeves from the larger tube. BTW this is how hand made lugs are done but with two larger tubes filleted together and cut about to form lugs.

I also agree with Mark's suggestion to use an external socket crown. Easier to feed braze into IME. This is where practice is most important IMO. A crown or steerer failure is pretty bad (done that twice...) and I've met riders who went down very hard when the only thing tethering the front wheel to the rest of the bike is a brake line.

If you're looking for frame parts at pretty low prices check out my For Sale thread. Andy.

Agree with the other Mark B, internal crowns make it harder to know you have full penetration. The difference isn't night and day — an experienced builder can make a fine fork either way, and I've seen external-socket crowns that had below-minimum penetration (the blade fell out of the socket). So neither crown comes with a guarantee you won't FDGB. Strength in that joint depends more on fit (clearances), surface prep, flux, heat-control, filler amount and timing, than whether the crown is internal or external. (Meself, I like internal with lugless, external with lugs, for aesthetic considerations only)

I wouldn't make a fork unless you have an 'old hand' there watching you. We aren't born with the perception it takes to see penetration. The other joints in a frame have redundancy, but not fork crowns. I trust your course teacher will be there watching you like a hawk (a hawk with brazing glasses?)

In frame operations large enough to have journeymen and apprentices (I've worked at several), newbs didn't braze a crown until they had lots of other brazing experience, like months or a year of full-time frameshop work. I can't imagine how a hobbyist could ever get that level of repetitive reinforcement of skills.

So, do you know yet what class you will take?

Oh and on the question of lugs, the one you show is made of sheetmetal that's bent around and welded at the seam. This results in a little air pocket inside, right at the joint where TT meets HT. This is not a structural problem, don't worry about it, and it can be a strong bullet point on the "pros" side of the pros-cons list if you want to manipulate them to a different angle to what they were made at. Lugs made in this millennium are all investment-cast, with none of that inside radius or the gap it leaves. Their ability to be tweaked to different angles is less than the sheetmetal or bulge-formed types. IC lugs almost always require less pre- and post-brazing cleanup to make them look nice, but that also makes the frame look more generic, takes away some of the individuality of hand-filed lugs. I have no problem with either type, just listing a couple differences.

But whatever type you choose, try to get some cheap/ugly lugs that you can braze with scraps of tubing to learn the process. Then try to break your sample joints, like in a vise, with a cheaterbar, to confirm strength. The tube should buckle before the braze breaks, really the braze should never break in such a test. Also saw up one or more sample joints to see cross-sections in key areas, to confirm you got enough penetration. That testing is time-consuming but hopefully your teacher agrees this is a worthwhile hurdle to clear before you braze a lug to actually ride.

All good input, so it sounds like I won't set my hopes on the Cinelli SC. Maybe someday!

I do plan on getting some practice in with some practice lugs and stress testing them/ cutting them up. I had seen the advice to cut up your first frame -- I don't want to have to do that! But I feel like with enough practice lugs cut up beforehand, I won't have to.

What are the cheap lugs some have suggested here? Long Shen?

And as far as which class, either Doug Fattic o'r Ellis Briggs, with a distant third choice being the Firsthand classes that will be offered in Portland. This is assuming these classes are still offered in two years, since I am requesting this from my wife as my gift for my 40th birthday/planned midlife crisis.

I was a high school teacher when I went to Ellis Briggs in Yorkshire in 1975 to learn how to build frames so I could share the secrets back here in the States. Going there (instead of almost any place else) was one of the best things that ever happened to me. I taught my 1st frame building class in the summer of 1976. My idea then (which has proved to be true) is that if material is properly organized and presented, it can really cut short the learning curve. 50 years later I think I am a better teacher now than I was then or anytime in between. It is possible to make a professional quality frame in class. It just takes longer than a pro.

To answer your 1st question the easiest fork crown for a beginner to braze is a full slopping outside socket model. This is because the entire socket is easy for the flame to access with minimum motion. More motion increases difficulty. For example the Pacinti fake twin plate crown is more challenging to get even heat on the inside socket wall because the plates get in the way of your flame.

There are 2 ways to approach a class. The 1st is to use the easiest materials to braze (like choosing horizontal over vertical rear dropouts). One of my primary jobs as a teacher is to reduce frustration and possible disappointment because of difficulties. Success doing easier brazing can lead to confidence to make a 2nd more challenging frame. The other way to make a more glorious frame is letting me do the hard parts. My classes are 3 weeks long (often done in different sessions) because it takes time to absorb the overwhelming information given. If I do the hard parts the class can be done in 2 weeks. I've had dozens of students that took other classes first before coming to me. They didn't learn enough the first time around.

Usually it is not a good idea to practice brazing before learning how to do it properly. I then have a hard time breaking bad habits. We don't cut up practice lugs in class. If done right it is obvious the brazing material when everywhere it should. And if you listen to instructions, nowhere it shouldn't so you end up with clean shorelines.

Many of my students come from an art background (I get lots of engineers too). They like the creative part of carving lugs. I'll post a few pictures of student made frames. Some like a simple design and some go crazy.

https://cimg0.ibsrv.net/gimg/bikefor...c35bb6180d.jpg
no frills Henry James lugs

https://cimg8.ibsrv.net/gimg/bikefor...aeb680bb4d.jpg
Adding cutouts to plain spearpoint Nikko lugs

https://cimg9.ibsrv.net/gimg/bikefor...76b0285a6e.jpg
cutting blanks lugs into more than just a spearmint. Notice the SS seat tube applique. H e designed and cut it out a sheet of stainless. The brand name is a play on words because he is from Michigan

https://cimg2.ibsrv.net/gimg/bikefor...2d9e443ee.jpeg
this is one of my favorites. She is a botanist and the trillium flower inspired here design

https://cimg7.ibsrv.net/gimg/bikefor...f735d34ce.jpeg
before it was painted. she did the designing and cutting and I did the brazing.

https://cimg9.ibsrv.net/gimg/bikefor...1641f4da5.jpeg
a high school band director's interpretation of lug and paint design.

https://cimg0.ibsrv.net/gimg/bikefor...7f80550d4.jpeg
This guy was from Turkey and his initials are in the front of both head lugs.

https://cimg3.ibsrv.net/gimg/bikefor...32c98e591.jpeg
bilams are possible too. This one is a half bilaminate with decoration on only 1 of the two tubes in each joint.

In addition to an external fork crown, I suggest external dropouts. Same business about being easier to feed in the brazing material.

https://cimg9.ibsrv.net/gimg/bikefor...66d2a5b1b8.png

Thanks for saying this, I meant to include this question but forgot.

Those braze like magic, with guaranteed full penetration, if you put rings of filler inside when assembling. Heat until filler appears all around the shoreline and you're done, zero post-braze cleanup needed.

The only difficulty, if you can call it that, is determining the diameter of mandrel to wind the rings around. A little trial and error there because of spring-back, but the rings don't have to be perfect.

Obviously don't insist on that if your teacher has other ideas.

Agreed. Internally lugged crowns are fine, but it can take a practiced eye to ensure that the brazing material has fully penetrated the socket; you have to be cognizant of the color change in the area where the brazing material has flowed. With an externally lugged crown, you have direct, visual confirmation of where the brazing material is or isn't. And a fork is not something you want to fail unexpectedly.

The very best lugs for a beginner to use are no longer being made but can maybe still be found. They are the Henry James lugs Hank Folsom had investment cast. They are the ones in my first picture of Steve's orange and white frame. The reason they worked well is because he made the down tube lug in the standard size version in 4 different angles. 57º, 59º, 60º and 62º. The other 2 lugs came in different angles too. This meant that a lug probably did not need to be blacksmithed to fit your frame design. When a lug needs to have its angle changed, the harder it is for a rookie to make them work. They didn't have long sockets making them ideal to braze. Of course you need to have a frame design already drawn to know which ones to get.

This is what i was trying to allude to earlier. Having the lugs match the design's angles makes the whole process much less challenging. I'll also add to the historical record and mention that HJ did offer his lower head tube lug in a 64* angle too. At least at first. I was happy to source a couple way back when i was making my first wife's Terry type frames. Those frames had lower head angles between 64* to 66*. They also had fairly narrow seat tube/down tube angles and thus needed some blacksmith work on the BB shell too. This was when I was happy that I had already begun to work with bronze for my seat lugs as the fit up with a heavily modded lug (angle wise) often resulted in larger gaps and such that 56% silver likes. Andy

I like the Henry James lugs too, it's a shame they're gone. Same with Llewellyn socketed dropouts. Looks like I should have taken this class a decade ago when these were all still available!

One more question, because I'm not totally understanding. With socketed lugs, one can wrap the silver around the tubing and fit the dropout socket over the silver, then heat until you see it come up to the shoreline (from what I'm gathering, I've never done this before so forgive me if I described it poorly). This is instead of feeding silver from the outside.

But this would be unacceptable for other lugs because... Why? Too deep of a braze? Too weak for a main tube (not that I want a dropout failure either)? One couldn't just wrap the Cinelli SC crown internal socket with silver, insert into the blade, and heat the blade (upside down) until silver comes out of the thin gap?

Come to think of it, I guess I don't really know how you feed silver into these internally socketed lugs in the first place.

I happen to be working with a crown that is very similar to what you first pictured. Here is how the filler (brass) is added to the joint. STick the brass coil into the tube, then let the crown socket push it in. You want all of the pieces touching as much as possible so heat transfers. This was my first attempt at making the brass coils for Imperial blades. I'm not quite happy with how it's fitting yet.

I flux it all up, then insert the coil and insert the tube on the stub. I heat the crown to near brazing temps and then start to add heat to up the tube. Once it's all at brazing temp, just flicking the flame up the tube to touch the area where the filler coils are. Once they start melting, you can see the color of the joint darken as the filler flows down between the tube and the internal socket. It's tricky (ie not beginner friendly without a teacher near by) to get full penetration around the whole joint so it's not really recommended. I did a bunch (a dozen?) of practice/testing before I used this on a frame/fork. I also have a boroscope that I use to inspect inside the tube after each one. One test I didn't get the filler all melted and a little chunk of brass was left loose and it would have rattled in the tube!

I'm guessing a similar approach is what others are describing for the external socketed dropouts, though, it's possible to simply feed it in from the outside as well like a standard lug. And I believe others have used preforms inside standard lugs with great success but I don't have any direct experience with that.

by https://www.flickr.com/photos/54319503@N05/, on Flickr

No you don't wrap filler wire aound the tubes, it has to go inside the tubes.

Main frame joints can be brazed with preforms too (preforms = shaped pieces of filler installed inside the joint). The process takes a lot of development and testing, not suitable for a beginner making one frame. The preform needs to have just the right amount of filler, and must be pressed tightly against the inside of the tube for best heat transfer, so the filler melts as soon as the joint is up to temperature. I think I brazed at least 50 sample joints and tested them before we committed to making frames for customers this way. Benefits include much faster brazing, like about 90 seconds for a typical lug joint, and zero post-braze cleanup. The filler comes up to the shoreline and just stops there, so there's never any spatter or blobs. It requires a lot of experience, judgment and quick reaction time from the operator though, absolutely not for beginners.

You might have better luck with preforms for fork crown brazing. I estimate I brazed around a thousand forks that way. It still takes a certain amount of trial and error to perfect the process, but less than with lugs. Ask your teacher if he supports that option. I'm not sure what I'd advise a beginner to do but preforms is probably more of an advanced topic for after you've built a few.

But for socketed dropouts, I'd call it a no-brainer, preforms are easy and there's not much that can go wrong. And you could prevent a failure like this, on a Rawland brand (Taiwan made):
https://cimg0.ibsrv.net/gimg/bikefor...188d453b6.jpeg
Probably wouldn't have broken if it had been completely brazed. After someone posted this pic on a mailing list I belong to, another Rawland owner posted his pic of the same dropout broken in the same way. Fully preventable with inside-out brazing.

Worry not, I have no intention of doing the fork crown this way and have rightly been scared off of that style fork crown for my first build. I was just curious why they were more difficult, because in my neophyte mind there's still an internal part and an external part regardless of if the lug is inside or outside the tube. And then I was also curious how you even feed silver or brass into those type of lugs, if not as a preform.

This has been very educational, and while so much of it will be up to what instructor I have, I can at least not get my heart set on some things and have a better idea of what my first build might be.

And I think I have asked this before, but fillet brazing is maybe not a "first frame" idea? Because I love the look and it seems like you get practice doing both types of brazing (fillet and lug) which could be good as an introduction. It sounds like Doug allows some students to do it that way, but his classes seem to run longer than some others.

Ay, there's the rub. When the blade is placed over the internal lug of the crown, there's just a vanishingly-thin line between the two, no gap at all if you've fitted the blade to the crown correctly. An external-socket crown has that shoreline, for you touch the end of the filler to. No such ledge or shelf on an internal crown.

One way for brazing internal crowns: Ceeway used to sell (may still do) this oval thing, whatcha callit, a washer? It goes between the crown and blade, and sticks out proud of the blade and crown.That gives you a shelf to apply filler to, and maybe most importantly, it lets you have an external fillet, that you file off after brazing, That ensures no visible holiday in the braze after filing.

If you have trouble envisioning that, here's an expertly-drawn schematic. Crown is the fat blue line, washer is the thin blue line, blade in red. Not to scale!

https://cimg8.ibsrv.net/gimg/bikefor...ae0283335c.jpg
There are other ways of course.

Trek's investment cast lugs, bottom bracket shells and socketed dropouts went through months of development and testing before we used them on production bikes. And the brazers were trained to look for proof of full penetration before removing the work from the fixture.

Some internally lugged crowns have pockets for preforms to be placed before brazing, e.g. the one on the left.
https://cimg4.ibsrv.net/gimg/bikefor...015c8e1fca.jpg

If it is possible for you to come to one of my classes before either one of us dies of natural causes, I have blank lugs in different angles given me by Jack Briggs when I left EB in 1975. They were probably made in the 50's. I've been using them sparingly but have loosened up that policy recently realizing my widow will probably throw them in the trash and it is extremely unlikely she will marry another framebuilder when I pass.

My student from Brazil that is here this week has done a nice craving on a set of those blank lugs similar to the designs that Alex Singer in Pairs used. Interestingly that general design is popular with my students and they have come up with variations like how long and wide the 3 points are among other possible variations. In fact if someone is not particularly creative, I have several different designs from simple to complex one can copy. We have gotten several feet of snow and the temperatures have seldom been out of single digits the 3 weeks he has been here. He has never seen snow before and is loving it. He is calling it his "Michigan experience".

My other student this month is doing a half bilam construction. He wanted a more sloping Top tube so he filed off the top tube socket leaving the part that slips over the head lug and will fillet braze the combination with 38% silver I bought from the Gasflux company. In other words the sleeves of the lugs are on the head and seat tube but not on the down and top tube,

Fillet brazing is generally easier for a student than lug brazing. They can practice more before making their frame and, if necessary, add more brass to a joint. However most prefer to learn how to braze a lug in case if they want to make more lugged frames and can leave class with enough knowledge to do a fillet brazed frame in the future.

I have no desire to build a frame set, but I think it is an outstanding project; worth the time, effort, and cost. Nice to see a very informative thread on this subject, with the photos being a huge plus. Thanks to the OP for starting it, and special thanks to the knowledgeable contributors. Awesome!
Subscribing to this one, a rarity for me


Going to subscribe to this one. A rarity for me.

So, timing can be interesting sometimes. With all this discussion about plugs and preforms I found myself doing this prep yesterday. I needed to extend the length of a stay (only one...) and create the top cap I was aiming for before mitering the stay tops for the seat tube. I decided to lathe out a plug to braze onto the top end of the stay. Simple enough and I went ahead with the turning work. With a fairly tight fit between the plug's shoulder and the stay's face I thought a preform of sorts would be good to try. I took a 5/16" tube, drilled a hole in it that the brazing rod (CO4, 1/16") just fits into and used the tube as the mandrel for the coils. I purposely made the coils a bit smaller in diameter than the stay's ID and pressed the coil onto the tapered shaft of a large drift punch. With that I could expand the coil's diameter fairly controlled, far easier than reducing a coil's diameter (ask how I know that one). Here's a shot of the prep work.

https://cimg3.ibsrv.net/gimg/bikefor...b405876145.jpg

Note that the plug ends that enter the stay and also butt against the coils are slightly beveled to better guide the flowing filler to the gap needing filled. The plug has a 3/8" internal drilling to reduce weight (so very important:)).

Because I like symmetry I cut down the second stay and prepped it too. Now some here will see that there's a bent and indented stay piece also in view (how many didn't notice this the first time?) This is the reason why I am doing all this. I'm making a frame, using stuff I have on hand and am trying to use old materials I've had for a while. A few years ago when i was making a MtB I tried to use these stays and with a MtB width of tire needed more clearance than a straight stay would offer. Well, this is how we learn, by trying something that doesn't work. I didn't toss the stay(s), knowing that my small projects might see them being recycled. When cut just past the bend/indent the stay it is just barely long enough. With the plug extension I have that extra 1/2" to play with and the stay top is nice and thick for further shaping after the joint is brazed up. Andy.

DANG...How did I not think of this even after taking a jewelry class recently! Smart!!

Looks like fun!

I like your bevel on the plug, to guide the filler when it melts.
There's another reason or two for that drilling, like taking out a substantial (and useless) heatsink, that slows down the brazing. You can't point the flame directly at that inside plug, so it only heats by conduction through the stay. And we like to keep the heating of the stay to a minimum. So the drilled hole up into the plug should be made as big as is still consistent with strength, i.e. the plug must never break.

And maybe for strain relief? To eliminate such a stark stress riser right at the end of the plug, tending to fatigue the stay. OK that maybe that is hardly worth mentioning, since seatstays never fatigue at the edge of their top eyes. But it's always good to eliminate sharp changes in section thickness, when you can.

The heatsink reason is the main one I think.

Mark- Actually the brazing did go fairly quick. I heated the plug first from its exposed portion and the heat carried up and into the stay quite well. After the preforms had flowed I went back to the "joint line" and added a little bit more bronze on top of it all around the plug/stay, I've seen way too many bikes "showing their slip" (when you can see the junction line after painting) to have that show on mine. What was really cool (and mentioned in an earlier reply here) was watching the "shadow" of the bronze filler flowing down along the plug. I usually don't see this as well as this time, but I also don't do a lot of bronze sweating of sleeves/lugs any more. Andy.

Here are some pictures of the blank lugs Raphael from Brazil designed and carved into a classic french style.

https://cimg8.ibsrv.net/gimg/bikefor...0cb228500.jpeg
Showing the blank lugs I got from Jack Briggs and the shape Raphael carved

https://cimg2.ibsrv.net/gimg/bikefor...98c0a43f4.jpeg
In the fixture

https://cimg3.ibsrv.net/gimg/bikefor...db31eddc1.jpeg
The seat lug

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".