some new kind of kick
ride quality: brazed lugs or welded better
I searched and read the thread about the relative strength of different
methods of joinery--brazing and lugs or welded frames. I was glad to find
that while lugs are stronger both welded and lugged frames are plenty
strong for the stresses of riding. What I'm really curious about is the ride
quality. If most people agree, or at least the Rivendell Reader attests,
that welded and brazed frames are strong enough--which has better
ride characteristics? Is there any difference? I mean, granted--
if you have a lugged frame built out of straight gauge hi-ten
compared to a welded 6-3-1 frame of course the welded frame
will ride better. But all things being equal (like tubing and butting
profiles) which is better in terms of ride quality--or is the method of joinery
unrelated to ride? People wax poetic about how the so and so frame of yesteryear
rides so well. I sometimes suspect that modern steel and butting profiles
allow welded framed to have as good of ride quality.
Basically there isn't a difference. There are three advantages to welding, ride wise:
- Unlimited geometry, so you can build a better riding frame without the limitations of what comes in lugs.
- More material choices, you don't see many lugged aluminum or Ti frames, and those materials can affect ride, though you would get some arguments as to whether either material is actually superior to steel
- Lugs add weight, so you have the option of repositioning lug weight to improve ride, Wouldn't bother getting my hopes up as to how major an effect.
- Another way of looking at unlimited geometry would be the options in tube geometry that opens up, that certainly can affect ride. Try finding a lug to fit square tubes.
I don't know of any evidence that lugs are stronger. Strength always has to be placed against factors like weight, and time to do it. With as big a materials and labour budget, I don't see any way lugs are stronger. For what lugs cost you could move to a more expensive tube material. Lugs cost about what ti tubes do, just for starters.
some new kind of kick
Thanks! I don't have any knowledge based on experience of in-depth reading. I just have several lugged and welded bikes. . . and I was wondering. I do appreciate the aesthetic qualities of lugs. I have heard (but have no way of confirming) that lugs are somewhat stronger. In the end my quest is really for a perfect ride quality. Springy but not too sluggish--with enough stiffness to get up an sprint.
Originally Posted by Peterpan1
Yea, Spectrum says the lugs are stronger but there is no clear evidence that this matters in the real world nor any proof to truly prove their claim.
Regarding ride quality, joining method doesn't matter - the gauge and size of the tubes is what determines how much the tubes flex. Some people think the tube strength determines flexibility but this is not true since all steel materials have basically the same modulus of elasticity - material characteristic that determines springiness.
I've seen more joint breakage on welded frames than on lugged frames. Pure anecdote, of course, but my opinion is that welds are more likely to fail than lugs. I also believe, though, that most riders will never experience a broken frame regardless of joinery methods.
As to ride, I firmly believe there is no difference, assuming the same materials.
All told, I'm pretty sure that the only "advantage" of lugs is cosmetic. This matters to me, but is of course not anything worth arguing about.
A few months ago, I found this relevant thread to be interesting enough to save it:
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.
seat tube - 350
BB shell - 100
head tube - 175
seat tube clamp - 25
seat tube 275
long shen BB shell 140
HT and lugs 180
seat tube clamp N/A 0
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!
lugs . . .
Lugs are not just limited to steel frames . . .
Here is an example of a carbon fiber lug (with window cutouts) on our all carbon fiber custom Zona tandem.
Asides from stenghtening a joint, they can be aestehically pleasing.
A good framebuilder can build equally strong lugged/non-lugged bikes.
Just our experience . . .
"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!!!"
Obviously that is the case. Making lugged racing bikes today is up there with horseshoes. If you actually listen to the stories of how some of these guys pursued old world craftsmen to get their educations, or look at the logos and details they use, of course they are living in the past. That is a lucrative market, the market for boomers who didn't get what they wanted when they were young. The other day I picked up a machine tool from a model steam guy. I always thought those guys were interested in steam because, well there is always someone who is. No, this guy didn't get to drive the steam tractor when he was a kid. Unfulfilled childhood dreams.
"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!!!!!"
Some of them are! There are plenty of guy who are at the same level but weld, Bike Friday crew or Don Feris come to mind. Don Feris is an artist with tig, Sachs builds on one of his jigs. Most of the guys who weld also braze, it's the nature of getting all the little pieces where you want them to go.
When you actually hang out at the frame forum, one thing I notice is a relative lack of interest in criticizing the joint choices of at least the "respected" builders. I think they know their choices are personal and not material. Sachs (lugs) seems to respect Feris (welds), and the wide variety of brazers.
When you talk about "best frame builders" is this a quantifiable "best" like their frames are used to win all the races, etc... or they are the best only because they make pretty bikes with lugs. I think the logic is chasing it's tail pretty quickly here.
The whole heat affected zone thing is nonsense for a variety of reasons. Mostly because on the materials used, in the configurations of those materials (butted) the heat in question is obviously within the design limits. Beyond that without stepping out on a technical limb I don't belong on. I both weld and make tools and heat treat in my shop. If you take a lowish carbon steel like 4130, and heat past the transformation temp, it doesn't harden. It isn't hardened in the first place. It isn't quenched. With care the heat cycling does not harm it. You want to keep the heat to the minimum so that the area being welded is protected by the argon, you don't want to remove the argon before it cools, but the heat affected zone is mostly just a term people have heard of. During welding the temper of these steels is not drawn, nor are they hardened annealed or normalized. It's basically a non-issue. Since a lot welding goes on without back purging you can be wrecking the inside of the tube, stuff like that can happen, you have to decide whether your butts are heavy enough, or whether you should back-purge.
Acetylene torch has about the same heat as an arc, around 5000F capability. In brazing a wider area of the tube is affected and the process takes much longer, but the material is not raised to the melting point. You get the potential of harm due to time and area, but it works out OK if you do it properly. You have similar issues about cooking the inside of the tube if you don't flux it thoroughly, which can lead to drawing too much braze into the tube.
At the end of the day, when competently done the materials can take both of these processes just fine. The tubing we use are products developed to be assembled by welding. In some of those regulated end uses the suggestion that these products should be brazed would lead to laughter. Welding is the approved method generally. The uphill fight would be for these other processes, it's just in cycling that this silly argument takes place.
I was just reviewing some info on gas welding, and in this text that was mostly chromo related, from a race car and aircraft perspective, the author made the following statement "always avoid brazing chromo steel..." Apparently it commonly leads to cracks in the tubes. Well I guess we know better. But good luck getting that lugged aircraft frame certified all the same.
When I say lugs aren't stronger though, it isn't really because of all these process related issues, it's because:
- You can adjust the nature of your joint to get whatever strength you want. That is what lugs are in the first place a means of increasing the surface area, and providing some material support to a brazed joint. Welders can respond to whatever strength requirements exist in a frame. There are things like gussets that for whatever perocial reasons aren't popular in certain categories of bike frame. But if you really want to drive a bike through hell, look at the details on BMX bikes. As I said, for consistency sake, give me materials and labour budgets equal to lugs and see where we end up.
- Joints aren't always the weak point in the structure anyway. There isn't any need for stronger than strong enough.
"Peter you’re incorrect about the heat zone being less in TIG welding. Here is a quote from Airborne Bicycles concerning what you said:"
The quote that follows there is BS. There is a "heat affected zone" on all bikes that are assembled with heat. HAZ is not a description of something bad. It is merely a description of the area that was affected by the heat. There had better be some such zone, or the brazing or welding would not occur. If you look at post assembled joints you can easily see from the oxidation on clean tubes what area was heated. The straw colour is in the 350F and up area. So you can't see the lower heat (you can touch it), but it isn't critical for much of anything anyway.
What a craftsman wants to know is whether they used massively more heat than the process was designed for. For instance if you properly TIG a tube your arc hits a tiny area and it instantly melts. Then you cool it with the rod, and move on. But if your arc wasn't hot enough or focused enough you wouldn't get that little spot to melt instantly you would heat a much wider area, and the weld might come out with steel that scorched included impurities etc... So the size of the heat affected zone is a useful check. The size of the heat affected zone is smallest for TIG because tig zaps a tiny are, melts it and it cools again. Comparatively at the other extreme a guy using a torch to braze has much of the countryside all aglow. The heat affected zone is a large area, and was nailed for a long time. But as long as the flux protected everything and the joint was properly made, who cares, they call it the heat affected zone, not the heat harmed zone.
It is often said that TIG is done because it is the cheapest, which is not true. It is the most expensive to purchase gear for, by a factor or 10 or more, the hardest to learn, and the slowest method of welding, short of gas. Even when compared to brazing it would be more cost effective for me to braze many small things like racks than to TIG them. Practically speaking I wonder whether stuff like Wal-Mart bikes really is TIGed it could be machine welded or migged.
Brazing is a great racket, it's easy to do, cheap, and it comes with an impression of a higher level of quality, if only in the cycling industry. It is perfect for the small shop.
edit: HAZ wise, some metals are seriously affected by the heats involved and would need to be heat treated following welding. I didn't mention this because the steels used in building are generally pretty forgiving.
Last edited by NoReg; 02-04-08 at 03:19 AM.
Originally Posted by Peterpan1
I agree with Peterpan; it's not the method of joining that's important, it's the quality.
Builders that put down one method over the other are spreading misinformation in my view; all three joining methods have been proven countless times which should be all the discussion that is needed on this subject.
Which method to join the tubes is a personal preference and nothing more. I like lugs but don't pretend that they do anything special in terms of adding strength.
I've done a bit of welding, (not on bikes) and I've done a bit of brazing.(on bikes and elsewhere) With lugs there is a lot of redundancy in the joint. Even a mediocre job of brazing will usually be strong enough. With welding, on the other hand, there are numerous ways to screw up that will lead to eventual failure of the joint.As just one example, consider the mitering....welded frames need excellent fit-up prior to welding. Lugged frames are stronger if the mitering is well done, but it most likely won't cause the frame to fail if there is a 2 mm gap on one side. As a second example, consider heat control: It matters when brazing, but you have to stray pretty far to cause more than cosmetic problems. Let your attention wander a bit while welding, though, and you have burned a hole through the material.....now a conscientious craftsman will scrap that tube or maybe even the whole frame, a hack, or an abused third world laborer might fill that hole, create a weak spot, and save themselves some money or a beating.
Originally Posted by Six jours
I'm not saying that craftsmen don't build lugged frames, just that welded frames will probably fail if the quality of craftsmanship is not high, while a semi-hack like me could make a lugged frame that while not so pretty as a craftsman would do, would probably still last a lifetime.
Bicycle Repair Man !!!
A good frame is a good frame whether it is lugged and brazed or welded and each has advantages for different applications.
The actual ride quality of a bicycle is less dependent on frame materials than it is on things like wheels, tires, saddles, and a good fit.
My 1978 Raleigh Superbe is built on a single gauge lugged frame and is one of the smoothest and most comfortable bikes I have ever owned... it also hits the curb at 42 pounds.
i didnt read through all of your posts but with me i think that a welded frame just allows the stress to concentrate more where with lugs or a big fillet it is spread out a bit more. tig takes a lot of power to break though.
Just for the benefit of people who don't weld and braze like you, and I...
" With welding, on the other hand, there are numerous ways to screw up that will lead to eventual failure of the joint.As just one example, consider the mitering....welded frames need excellent fit-up prior to welding. Lugged frames are stronger if the mitering is well done, but it most likely won't cause the frame to fail if there is a 2 mm gap on one side."
Seems as though a large number of people making frames, pro and even amateur, are using milling machines and expensive hole saws like the Strawberries, to cut their miters, probably not accurate to 2 thou, but a lot nearer that than 2 MM. not to say that a file would yield different results, it just take longer as much as 100 minutes longer per frame. Which really isn't much, but even the small shop can buy a second hand mill for 500 bucks easy, and drop that cost and effort level a lot. Factories can use anything from laser copers to specialized tooling to get tight miters.
It doesn't appear to be well known but it isn't necessary to have tight miters to weld well. There are techniques for gap welding the tubes efficiently, and these are commonly used in aircraft. Since the intent is to build up a very large fillet weld in most bike welding this isn't done, but the reason for the tight miters is as much to make the jigging easy, and aesthetics, and not really much at all to do with the resultant strength. Gap welds actually fascilitate penetration. Holes are another thing!
"As a second example, consider heat control: It matters when brazing, but you have to stray pretty far to cause more than cosmetic problems. Let your attention wander a bit while welding, though, and you have burned a hole through the material.....now a conscientious craftsman will scrap that tube or maybe even the whole frame, a hack, or an abused third world laborer might fill that hole, create a weak spot, and save themselves some money or a beating."
The real issue is quality control. One can tell when a TIG joint is garbage. It translates on the finished product, and it translates while it is being done. Ugly welds are often very strong. In the current market lugged frames are mostly a premium product, though lugged forks are made cheaply enough. At the premium level, the quality of workmanship shouldn't be an issue for either lugs or TIG you get down to the fundamentals of the two methods, and there really isn't any reason to suspect either method. If anything, TIG ought to be better, only because the TIG guy is really at the mercy of how his welds look, he can't hide them with his 21st century versions of dimly understood, heraldic imagery. TIG is right out there for all to see, and it needs to be spectacular at the custom level. I assume that is a distinction without a difference, but it would be a good thing if more people could at least distinguish welding.
"I'm not saying that craftsmen don't build lugged frames, just that welded frames will probably fail if the quality of craftsmanship is not high, while a semi-hack like me could make a lugged frame that while not so pretty as a craftsman would do, would probably still last a lifetime."
At the end of the day brazing is easier to learn, as you say. There are also machines that do the brazing automatically, there was a time when "all" the cheap bikes where lugged, even if the lugs looked like plumbing fittings. Some factories still do it. Surly it turning out lugged forks that retail for about 60 bucks. It's all good.
"welded frame just allows the stress to concentrate more where with lugs or a big fillet it is spread out a bit more"
It's true that brazed joints need more surface area to be strong. And it's true that welded joints don't, therefore the loads will be carried over wider areas with the brazed joints. If welded joints needed larger areas of contact there are many ways that could be achieved. In fact, the style of TIG welding used in bike manufacture is a hybrid of fillet welding where the actual size of the joint is bigger than need be. The real size required to weld a .9MM tube wall (typical chromo) would yield a bead width of about 2mm, while the usual bead is much wider. On fancy expensive tubes with thinner wall it would be thinner still. So one may think the TIG joint is over a small area, but it could be a lot smaller and full strength.
It's also worth noting that bikes cleverly triangulate the tubes to create groupings of tubes that distribute the loads into the joints evenly. The head tube fork area being the exception.
It's like anything else the points raised do identify the "problem". But design and proper execution allows these points to be dealt with, placing everything at whatever level of quality and efficiency the customer requires.
Welding bike frames has been around a long time. Back to the early part of the 20th century, when some prominent bike manufacturers used to have "Welding" in their name. TIG came out of WWII, but started to show up in quality bikes by the late 70s.
I was just reading some stuff on air hardening steel on Bob Jackson's site which seems to suggest the "interesting" notion that TIG is worse because it hardens less of the steel in the joint region. This is a new to me reverse heat affected zone hypothesis. First, it may be true, who knows, who really seriously tests this stuff. But there are a number of aspects to it.
1) The joint is where the join is between the tubes, Overshooting that area and hardening all around it is just messing with the tubes, that "benefit" has to come to an end at some point.
2) If this hardness level is so necessary, why not just heat treat the tubes all over. Aside from cost I mean.
3) There are alloys like 953 that are supposed to be heat treated. Can we just flame these with our oxy torches and expect master heat treater results? Anyone got a Rockwell tester (I do by the way). People who play around with various proposed benefits to air hardening, seem to have a lot of faith in haphazard by-product heat treating.
There are a lot of observations like these which simply observe stuff that is happening, and then attribute positive or negative attributes to outcomes however random they may be in relation to a claimed benefit. A facile analysis. A chain is only as strong as it's weakest link. Hardening one "link" only will not stop the adjacent one from breaking under tension. On the other hand give the strong man a bar to bend and whether it was hardened or not will mater a lot, even harbening just sections of it may be as critical. You have to look a lot deeper than single point changes. You have to look at how they affect the structure and the loads coming on it. That analysis is too complicated in this instance. People are just nailing together tubes not creating intentionally, diferentially heat treated structures like Samurai swords.
Last edited by NoReg; 02-11-08 at 09:05 PM.
my thinking on this is that the reason to choose lugs over Tig or Brazing is for strength. if your a heavy person and tend to be tough on bikes then lugs are the way to go, or brazed. I'd go for Tig or Braze if i weren't hard on the bike. plus you have the looks to think about too. lugs can be a real thing of beauty if you really get fancy, i also think that brazed can give that nice smooth sexy look too, like a carbon mono frame. the frame just flows from joint to joint. certain Tig frames can look like brazed if the welder is good. my Wojcik is Tig'd and it looks almost like it was brazed. so if you think and know how you treat and ride, making the choice can be alot easier.
"my thinking on this is that the reason to choose lugs over Tig or Brazing is for strength."
That's the part that isn't true at all, and never would be. Every other industry from aircraft to nuke plants does not follow that principle. But even if it were true that lugs were quantifiably stronger, which it isn't, but let us say for fat people, or on a unit weight, or a monday, tigged bikes would only be weaker if they didn't beef some part of the joint up accordinly to make them equaly strong. How do they make tandem TIG bikes, or TIG cargo bikes.
There isn't any such thing as "stronger". It is always stronger in some regard, by weight or whatever, and the response to that is simply to adjust the structure. Even in today's litigation environment, with crap bikes, offered through cash rich companies like Walmart, or anyone else, there is no evidence of that strengthening. The pros who do the horrible Paris Rubais race, race on cheap TIG Cyclocross frames (some of them) because the vibe is better than their regular ride. Surely if strength was a problem they could get something other than TIG.
The only reason TIG bikes are looked down on is that they came later, and promised to, and did put the lug builders out of the picture. For a while people who never held a TIG torch made up fantastic reasons as to why TIG was inferior for strength and other reasons. It's all bogus.
Much of this argument no longer exists among pros who know the market is there for a variety of steel frames, and the more people making them the better for the overall industry. One of the few things that actually supports the existance of lugged bikes today is the widespread popularity of TIG steel bikes. Imagine how much easier it is to sell a lugged bike when people like Surly are selling tons of Tigged ones. If the whole industry had moved to Aluminum or carbon, it would depress further the credibility of steel frames of any kind.
some new kind of kick
I don't think anyone is saying tigging isn't strong. It is plenty strong. But
numerous people, several of whom are quite credible have told me
that brazed lugs are stronger than fillet brazing which in turn is stronger
than tigged work. I think all of these methods of joinery are
more than strong enough for the normal stresses of riding--assuming
the bike is engineered correctly and doesn't concentrate stress. But I have heard
that tigging is not as strong and fails at a lower threshold than brazed lugs. Other industries
probably do tigged welding because it is cheaper?
Originally Posted by Peterpan1
but wouldn't a joint that is held together with a lug be stronger than a Tig because there would be more surface area welded with a lug? lets use a top tube to head tube for example. Tig would be tube to tube, weld joint, end of story. a lug would give you 2 areas to weld to, top to lug and head to lug. isn't that a way of looking at it?
Good question. The short answer is that the weld is made with continuous steel, and doesn't need the additional surface area to reach the needed strength. It is as though the top tube and the head tube were one single piece, though in practice that kind of continuity is not going to happen, but the results are sufficient for bikes and aircraft for the last near one hundred years.
The other part of the answer is that whichever joint is stronger, one doesn't need "stronger than strong enough". We are just after strong enough, and TIG is the industry standard of "strong enough".
One could make a lug so large it would entirely cover the top tube and head tube, and once brazed in place that structure could very well be stronger in some chosen test than the tigged together tube, it being probably at least twice the weight. But you wouldn't want that bike, because it would be too heavy.
YOU could also take that weight budget and just weld together tubes that were twice the weight, and that would also give you a structure that is stronger than strong enough.
When a bike is welded together or lugged together, one can get the required strength from either system so making either one "stronger" isn't required.
The question that interests me is having built bikes by welding their frames in the early 20th century, when and why did we forget that technology, even as we used it extensively in the aircraft industry? I think part of the reason is that lugs are faster/cheaper than welding. Harley Davidson frames were brazed together during the post WWII classic period. And the kid's bikes I rode with high handlebars and banana seats in the 60 also had lugged frames. Then in the 70s when the 10 speed European bikes took over, the best frames were artistically lugged together, with lugs whose designs copied from European heritage symbols. Then in the late 70s someone tigged a bike frame together and the party was over. But I really don't know the history.
so is Tig'ing a frame quicker than using lugs? my only thought about your point of the late 70's is that bikes started being mass produced more in China (or somewhere else outside the US) and that Tig provided the fastest way to keep the production line moving.