Been thinking about this for a while and thought I would get the wisdom of the forum.....why did/do lugs (internal or external) persist so long on steel framed bicycles (not talking about new fangled aluminum here)? I have been around vintage motorcycles forever and one of the turning points for a manufacturer of mc frames is when they stopped using lugs (heavy cast bits) and started using "all-welded" construction, yet we continue to see lugged steel construction even today, on very lovely and high end frames.

I admit I love the looks of a lugged bike but I also love the workmanship in a beautifully crafted italian motorcycle without them (or I like to laugh at the bubblegum welds on spanish dirt bikes of the 60s)....so what is the reason behind the persistence of lugs?

On a related note, if you are going to use lugs then why braze the tubes - why not space age glue? Never have to worry about warping or heat treatment.....

Mark

Lugs permit the builder to use lower-temperature brazing instead of higher-temperature welding. In theory, this in turn would enable one to use thinner-walled, lighter-weight frame tubes.

As for glue, I do not know the strength and longevity of a glue bond versus brazing, but it sounds like a reasonable idea.

This thread, quoting some of the world's finest framebuilders, gives some pretty persuasive arguments for using lugs. I thought it interesting enough to copy and paste it into a Word document.

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Froze --

Peter you’re incorrect about the heat zone being less in TIG welding. Here is a quote from Airborne Bicycles concerning what you said:

"How you weld a standard metal frame together is very important. For steel you can use lugs, TIG welding, or fillet brazing. Lugs add weight, TIG welding is good on weight but it actually melts the tubes that are being put together and creates a heat affected zone (HAZ) in the tubes that may eventually lead to a failure. The fillet brazing uses a brass-silver “glue” that gets melted in to hold the tubes together. This is actually the best system, since the tubes don’t form this HAZ, and the braze is strong enough to hold it all together. For aluminum, the most common practice is TIG welding, and most Aluminum frames will fail at the welds due to the HAZ in the tubes. Ti is also TIG welded, and has the same problems as Aluminum. However, especially in Ti 6-4 you can find frames that are welded with commercially pure Ti (CP) instead of Ti 6-4, and therefore this acts like a fillet braze”. In theory these frames are stronger since the HAZ is smaller in the Ti tubes as the CP Ti brazing material melts at a lower temperature than the 6-4 Ti tubes, so the tubes are never melted in the welding process."

Then there's the following from Rivendell:

"Methods of construction: Brazing a frame with lugs is the most time-consuming way to make a frame, and is the least popular, and generally least sought-after way. So those who do it are either fools or have good reasons. A properly designed and built lugged steel frame is the strongest and most beautiful. It ought to also be the most expensive by far, but often isn’t.

Brazed, with lugs: Pro: Makes the strongest joints. Simplifies tube replacement, so a crashed frame needn't be thrown away. Arguably the most interesting joints, since lugs are available in a variety of styles, and offer the craftsman more creative options.

Con: It's takes more time, therefore it costs more; and there's a shortage of good brazers. The lugs have to more or less match the joints, and many modern "high tech downhill" style bikes have joints that nobody makes lugs for.

TIG-welded: Pro: Fast, economical, strong, and versatile. Any tube configuration can be TIG-welded, because there are no lugs to deal with.

Con: High heat levels are concentrated at the most stressed area of the frame. Melts the underlying tube, making tube replacement impractical-to-impossible.

What is a lug? A sleeve of metal that surrounds the frame tube at the joint, strengthening the joint. Most modern frames don't have them.

2. How come? They're more expensive to build with; and from a strictly practical point of view, they're unnecessary.

3. What does a lug do? It strengthens the joint by adding material to the stressed areas, and distributes the stresses over a large area. And it adds an artistic element to the frame joint. And it allows tubes to be joined by brazing, rather than welding.

4. Why brazing rather than welding? Less heat, mainly, and one of the benefits is that the tubes themselves are not melted. So, if you crash and bend a top tube, for instance, it can be replaced and the frame made good as new.

5. Are all lugs alike? No. Some are well-designed to eliminate stresses. Others cause stresses. Some are thick, some are thin. Some fit the tubes well, others don't. Some are rather plain, some are rather ostentatious. Some are generic and available for purchase by anybody, others are proprietary and unique to one brand of bike. Some are hand-cut and one-of-a-kind. In addition, lugs can be made by any of several methods, including but not limited to investment casting, stamping and welding, die casting, and machining.

6. Is there any reason to get a lugged frame over a glued or TIG-welded frame? Well, it depends. From strictly a functional perspective, in the short-term life of a bicycle, it makes no difference whether the frame is lugged or not. And, if you plan to get a new frame every couple of years, then the long-term benefits of a lugged frame (durability and the ability to replace bent/crashed tubes) don't work for you. Likewise, if you prefer the appearance of TIG-welds, then you won't be talked into lugs, no matter what."

Then there's this from Henry James:

"Steel is the only metal that can economically and technically be used with lugs. These simple sockets at each frame tube joint reinforce the joint to improve strength, reliability and (fatigue) life. Silver or brass brazing completes the structure with minimal metallurgical damage (unlike welding which must melt the metal under essentially uncontrolled conditions). The hype put out by aluminum and titanium makers is that welding is stronger, lighter, the latest technology, and magically better. In fact, they can't use lugs and have no choice but to weld, and so they turn to hype..."

Then there's this from Kirk Frames:

"Kirk frames are made exclusively of brazed steel. I use steel because it offers many advantages, including: Ride quality, Fatigue resistance, availability of tubes with a wide variety of specs, Cost and Reparability. Steel's combination of stiffness and fatigue resistance allows smaller diameter tubing compared to titanium or aluminum. Tubing diameter is one of the main factors that influences ride quality. For example, aluminum tubing needs to be large in diameter due to its poor fatigue resistance. Titanium, on the other hand, is much more flexible than steel so it needs to be large in diameter to be stiff enough to handle properly and transfer energy. Steel tubing offers a balance of a supple ride and durability that make it a choice building material.

Brazing: Traditional brazed joints are the choice for Kirk frames. Some advantages of brazed joints are: Lower heat compared to welded joints, Smaller heat-affected zone, Allows for the use of thinner tubing and Aesthetic qualities. Brazing heats the steel to about 1,800 degrees F - just hot enough to allow the brass or silver to melt and flow into the joint. Welding, by contrast, heats the tubing to its melting point (around 3,500 degrees F). At this temperature annealing occurs in most tubing, causing a weakened area adjacent to the joint. Brazing allows for a much smaller heat-affected zone than welding. The use of lugs or fillets spreads the load over a larger area than a welded joint. This can allow the builder to use thinner tubing for a given size rider, without risking failure."

And there's Spectrum Cycles:

"Our steel frames are lugged for two reasons. Lugs are stronger and lugs are beautiful. Did we mention that lugs are stronger? Almost all mass-production steel frames produced today utilize cost-effective TIG welding to join tubes. This prompts a question: why do we still use silver soldered lugged joining? Because properly fitted and soldered lugged joints are considerably stronger than joints created any other way.

On Strength: In the late '80s, a team of scientists in the UC Davis engineering department undertook an in-depth look at the relative strengths of various steel joining techniques at the request of "Bicycle Guide" magazine. The three top frame builders associated with the three primary joining techniques were asked to supply joining samples using tubing supplied to the builders from the same mill run. Tom Ritchie provided the fillet-brazed samples, TIG-welding was done by Gary Helfrich, and the silver soldered lugged samples were done by Spectrum's Jeff Duser. The samples were fatigue tested, in some cases to failure. In most cases, the joints did not fail. More often, the tubes failed at or near the joint. The team's study involved microscopic analysis of the crystal structure of joining zones, heat effected zones and failure sites. They concluded that all three joining techniques, done properly, are clearly of sufficient strength for the purpose of bicycle frame construction. The different results obtained from the samples resulted primarily in the heat-affected areas of the tubes themselves. Not surprisingly, the tubes that were soldered turned out to be stronger than the tubes that were welded or brazed. So, what does this mean in the real world? Frames built with silver soldered lugs will last longer than those that are fillet brazed and considerably longer than those that are welded. However, for most of our customers, the real practical difference is that lugged frames hold up in crashes better, and when it becomes necessary, they are much easier to repair. On Modern Air Hardening Tubing: The latest generation of air-hardening steel tubing used by top quality welding frame builders was not available at the time of the UC Davis study. We at Spectrum expect that this tubing, when in the hands of master builders, is more reliable than the welded joints and tubes tested at UC Davis but still less strong than lugged joints.

Then let's not forget the master Richard Sachs:

"Most of the racing bikes you see today use mass-produced frames made out of carbon fiber (light, but extremely delicate), aluminum (light, but delicate and brittle to ride) and titanium (light and durable, but aesthetically crude). Because of economic reasons, the handmade lugged steel bicycle frame has become practically extinct. In the long run it's much less labor intensive to create molded carbon fiber frames or TIG welded aluminum frames than it is to join steel tubes together with a 56% silver brazing compound and a set of lugs.

Amazing how most of America's best frame builders still swear by lugs and brazing...why? Because they’re locked in the past? Refuse to grow up with the technology? Stubborn refusal to comply? NO!!! Their reputations are on the line for all the bikes they make, and if they felt welding was superior they would ALL be doing it!!!!!

Dave Kirk –

This is an interesting thread and got me to thinking (scary I know). What is the real weight difference between lugged and TIGged. It of course matters what lugs are being used (some are lighter than others) and the tubes and such.

Well I went into the vast "Kirk Frameworks center of weights and measures" and broke out the kitchen scale and came up with some interesting numbers. My idea was to weigh the frame components that differ when building a lugged versus TIG bike. They are-

Seat tube - on a lug bike it needs a seat lug of course but it doesn't need an externally butted seat tube (reinforced with a heavier wall at the top to handle the clamping duties). The TIG bike also needs a slip on clamping collar.

Bottom bracket - both types use a bb shell of course but the lugged shell has more to it so the weight differs.

Head tube - a lugged bike has....head lugs while a TIG bike does not. But the TIG bike has a heaver walled tube to deal with the loads and headset stress.

TIG welding rod versus brazing rod - a really tough one to estimate. I'm calling it a wash. I'm sure there is of course a difference but it can't amount to much. I'd guess that the brazing rod is a bit heavier and for the academic exercise of it all I'm going to research into this and find out some real numbers. But as stated above it can't amount to much as neither rod weighs much to begin with.

The measurements were taken on Reynolds 725 tubes that were the same length. The lugs are standard Richie Sachs lugs. Weight is in grams.


TIG

seat tube - 350
BB shell - 100
head tube - 175
seat tube clamp - 25

total 650


LUG

seat tube 275
long shen BB shell 140
HT and lugs 180
seat tube clamp N/A 0

total 595



Now I can here the screaming out there (sssshhh!). I fully understand that my kitchen scale is not the most accurate device known to man but it's fine for a comparison I think. I fully recognize that this is a bit crude and that the brazing rod might add a few grams the lug side of the equation but anyway you cut it the weight difference between a TIG and lug bike is minimal and might even favor the lugs bike by a few grams.

I think that this is in line with what we see available out there.....a good steel frame weighs about 3.5 to 3.75lbs no matter how you put it together.

Let the flaming begin!

Dave

Lugs look cool. You said it yourself: "...on very lovely high end frames".

There was a time when the best tubing available for bikes had to be lugged. Or fillet brazed. That caliber of tubing was far too thin to be "welded".

Nowadays, awesome frames can be TIG welded, brazed, lugged. Aluminum frames are typically TIG welded because it can be done by machine. Same for the thicker tubing used on motorcycles.

Newer steel alloys allow lugs, brazing, and TIG welding. It's all up to the builder and the buyer.

Glues have been used in the past and I believe that's how carbon fiber bikes are held together. Brazing is just another name for gluing tubes together except it's either brass or silver that acts as the glue. Not sure why they don't use glues today except maybe they don't work too well.

It's purely a matter of aesthetics. The pros done use either any more.

High end, mid end, whichever end. They just plain look cool.,,,,BD

But most motorcycle frames are made of what is known as gaspipe in bicycle circles. That stuff could be arc welded with no problems, just like the cheapest bicycles. (Well, okay, there were some racing frames made of chrome moly, but it was still welded and I never heard of 0.5mm thick double butted tubing being used to build motorcycle frames.) Okay, today there is lightweight high alloy steel that can be TIG welded, but those joints look like crap compared to lugs or fillet brazing. So today you have KOF (Keeper of the Flame) bikes that are lugged or fillet brazed because that's the traditional way and looks cool, not like a frame TIG welded on a robot production line in China.

FWIW, I just picked up a used Gunnar for this race season, and I love it. It's lightweight, rides like steel should ride, and clearly takes abuse without complaint (this will be it's seventh season). TIG welding might be less attractive than lugs, and maybe it is nominally heavier, but I have a hard time believing that the strength is compromised in a meaningful way. I plan on keeping this bike for a long time, so I guess we'll see in 30 years how it's holding up.

I realized this is sort of OT, but I'm smitten with my TIG-welded bike and I felt like sharing.

Photos?

Lugs are sexy.

East Hill

Why lugs?

Because.

Besides. East Hill considers them sexy.

I don't have any photos yet. It's too cold to go outside and stand around taking photos, and I'm not comfortably with Bikes Forums members knowing how I've decorated my house.

There may be another reason that lugs have persisted so long on "very lovely and high end frames" as you point out: aside from them being very attractive, people with enough money to afford "very lovely and high end frames" are usually older and came of age when lugged construction was considered the best way to build a frame. Welded construction was used only on the cheapest department store bikes that weighed 40+ lbs. Fillet brazing was not as widely known and while used on many fine Schwinn frames, it was often confused with the electro-forging process used on the cheaper Varsity/Continental models. So if you are a well-heel gentleman (or lady) of a certain age and you want to buy a high-end frame, there is a very good chance that you will look for a steel frame of lugged construction because that's what you grew up with and are familiar with. And frame builders know their customers and will build accordingly.

Time will tell if in 20 years the cyclists of the day will still be interested in lugged steel or if cyclists who grew up with TIG welding and carbon fiber will prefer that methhod of frame construction.

Lugs are NOT 'all metal sleeves' on steel bikes.
Photo of our lugged (with window cutouts) BB-shell on our all carbon fiber tandem.

In 1971 I was at the local motorcycle dealer, and he had the latest Penton Motocross & trials machines with Reynolds 531 transfers on the frame and swing arm!
Its a question of money.

An interesting aside, in the aircraft industry, 4130 needs to be welded, not brazed. but also required post weld heat treatment for engine cradles and mounts, usually done mounted onto huge cast iron fixtures to keep from heat distortion, that after a number of cycles need to be replaced. Brazing with brass is not allowed due to the possible creation of micro cracks where the brass infuses in the steel grain structure and cools at a different rate, creating a surface layer of micro cracks that can grow.

Why fillet brazed bike frames don't fall out of the sky (pun intended) all the time I do not know. But, Reynolds 531 is a bit different than Columbus of the day, columbus being closer to 4130.

I do agree with the other previous poster that a tigged steel frame is probably heavier than a lugged one, or can easily be. The weight of thicker butted ends & head tube wall thickness coupled with seat tube sleeves (I forgot to count the seatpost binder collar)

That looks gorgeous! I know it's not C&V but can we see the rest of the tandem?

My new Sherpa 30 touring bike is made out of Reynolds 853 tubing.
No lugs.

This statement confuses a couple of different issues. Whether or not lugs are purely an aesthetic choice is one question. However, the second sentence doesn't follow from the first one. An important question to ask is whether or not what pros use is what makes sense for the average rider. Pros get new bikes every year. They usually don't even choose those themselves. For them, a few grams may be the difference between staying with the lead group on a long climb or dropping off the pace. I'm not sure what pros do or don't use goes straight to the issue of what the average (or below average, or above average) recreational rider needs and would want to ride for, say, 10 years.
That said, I agree that the use of lugs is largely on aesthetic grounds.

Most framebuilders agree that with the air hardening steels we have available today, any of the three major tube joining methods (brazed lugs, fillet brazing, and TIG welding) will render frames that are sufficiently strong to withstand normal use over many, many years, and the joints properly made using any of these methods are likely to be stronger than the tubes themselves.

Well, ok. Perhaps when the weather warms up?

East Hill

So, in other words--lugs are sexy .

East Hill

I can't speak for others, but yes; to me lugs are very sexy.

These are Richard Sachs' stainless Newvex lugs:

Mine aren't quite that deleriously happy, but they are still sexy !

East Hill

Gnome in Kiwi-land:
While our carbon fiber tandem is not exactly vintage, it has a bit of classic (and unorthodox) look.
We designed it and Bob Davis in Arizona (a retired aerospace engineer) built it. Currently has 17,000+ miles on the odo.
Have owned several custom steel tandems, a couple of them lugged and one fillet brazed.
Here are photos of our tandem (and the happy owners) as you requested.
Pedal on TWOgether!
Rudy and Kay/zonatandem

Thanks everyone for the comments: and let me start by being clear - I love lugs too! Mostly for the look - they add tremendous interest to the frameset. So the question was rooted in the engineering question: are they only for show or is there a functional reason they need to be there.

The responses were pretty clear: A good builder can, with modern materials and equipment, make a very viable frame from steel without lugs, while driving weight down and not compromising strength or stiffness.

I agree motorcycle frames tend to be heavier tubing that can stand welding, but as at least one other poster pointed out there are racing mc frames made with very similar tubing to what we find on our bicycles (proportionally expensive too!). Daspa in Italy made some amazing, lightweight, stiff (and fragile) frames for NCR to use in endurance racing as far back as the 70s. A 12 lb frame to contain over 100hp at 150mph is an amazing feat of engineering, with absolutely stunning welds and no lugs....

Anyway, thanks everyone for the input!

just another way to build a bike. And an opportunity for some self-expression. And, no, just because I'm an old fart doesn't mean that I automatically assume that an expensive bike needs lugs (maybe...nah). And I think hips are sexy, myself.

And, there was a major manufacturer (Raleigh of America) that assembled bikes with glue and lugs (the Technium line) for years. Unfortunately I found them kinda ugly for my refined tastes (they were internal lugs). heh. Trek has glued its aluminum bikes together for over 20 years. Vitus actually glued its tubing into external lugs, and several other similar manufacturers (alan, etc) did as well. The glue is still holding up on those bikes in my garage...but I don't ride 'em much any more. Steel lugs are prettier. and I guess y'all are right. Sexier, too.