rydabent

Which is stronger a lugged frame or a butt welded frame. I for one believe the lugged frame would be stronger since welded at a lower temperature. I know there have been advances in tube technology, but still. If you read all the bike books especially during the 80s and earlier, they made it absolutely clear a lugged frame was superior. Have there been any actual tests done to compare the two different build methods.

This question is based on the fact that bike companies want to maximize their profits. Having a frame butt welded up by a robot just has to be much cheaper than having a lug frame brazed by a person. And of course there is the additional cost of the lugs.



What say you.

Homebrew01

All manner of tube attaching techniques appear strong enough to withstand human power.
More important, imo, is materials, design, aesthetics...

DrIsotope

I can't say which is superior, but I can say that my frame has both, and I imagine they did that for a reason.

CliffordK

Theoretically one could profile the tubing so that the butted ends are thick enough to prevent failure at the welds under ordinary conditions.

For failures of lugged bikes, browsing photos posted, I think it is just as common for lugs to fail as for tubes to fail (with failures usually along the stress point along the edge of the lugs). Perhaps it depends on lug material and construction.

The super-light steel frames (Reynolds 953), lugs would be a significant portion of the weight of the frame, and might not be made up for with additional strength. I.E. You couldn't make the tubes thinner and lighter just because of adding lugs.

Anyway, I like the character of lugged bikes, but today, it may not have any real benefit.

dabac

Don't think you can make a sensible comparison on two points alone.
You'd need to add something like "at comparable prices and/or weight".

jgwilliams

I don't know but I can say that a lugged frame is strong enough. Some years back I had an accident on my bike when someone opened a car door in my path. The front wheel took the brunt of the impact and collapsed. However, when I got the wheel repaired it was clear that the fork had also bent slightly. I was later able to get it retracked and I'm still riding that bike, which is a 531 butted frameset. So it's pretty clear that the brazed lugs were strong enough to take anything that the tubing could handle. In those days the forks were also made with brazed lugs, unlike modern one-piece forks.

I'm sure that welding could be stronger but I'm not sure that it matters. In the quest for weight reduction the tubing itself is relatively susceptible to impact forces in an unexpected direction.

Trakhak

The books that the OP cites, published in the 1970s or thereabouts, weren't claiming that lugged construction is inherently superior to lugless construction; they were simply describing how to distinguish the bikes then sold by bike stores (almost all with lugged construction) from bikes sold in department and hardware stores (butt welded).

Lugged construction isn't inherently superior to other modern methods of tube joining. In fact, lugged construction was originally introduced to increase profits by eliminating the need for precise tube mitering and for highly skilled workers. Lugged frames began to require sophisticated joining techniques only when lightweight, high-strength, thin-walled steel alloys came into use sometime in the 1920s or 1930s.

jgwilliams

Interesting - I didn't know that. It makes sense, though. I remember reading that one of the Reynolds tubes in particular (was 753) required special care and frame builders had to submit a sample of their work to Reynolds for quality testing before they were certificated to build frames with it.

indyfabz

Subscribed.

bmthom.gis

haha you said butt.
I have nothing else to offer this thread

Retro Grouch 

[QUOTE=rydabent;19407783]This question is based on the fact that bike companies want to maximize their profits. Having a frame butt welded up by a robot just has to be much cheaper than having a lug frame brazed by a person. [QUOTE]

Last week you were complaining that prices are too high. Today you are poo pooing cost cutting measures.

JohnDThompson 

Both are equally strong when competently done. Modern steel alloys are optimized for automated TIG welding, which makes such frames very economical to produce. And welding frees the designer from constraints of frame angles and tubing diameters.

stanman13

The weld can be made stronger than the base metal. A brazed joint is probably also stronger than the base metal in the case of the thin tubing of a bicycle. Theoretically the weld is probably the stronger of the two joining methods, but for these purposes it just doesn't matter.

Incidentally, you won't find any butt joints on a bicycle. They are all fillet joints. (I'm a former welder and current AWS Certified Weld Inspector)

Trakhak

We love lugged frames, but it's an acquired taste. Except for the occasional fancy paint job, chrome, etc., for most people who don't care about bikes, lugs on steel frame tubes have all the appeal of an elbow joint on a gas pipe. If they had to choose which looks better, they'd likely pick a swoopy carbon frame over a skinny steel frame every time.

Tombaatar

Get the scientists working on the tube technology immediately.

rydabent

[QUOTE=Retro Grouch;19408389][QUOTE=rydabent;19407783]This question is based on the fact that bike companies want to maximize their profits. Having a frame butt welded up by a robot just has to be much cheaper than having a lug frame brazed by a person. Yup------------high prices, and cheap construction.

Up North

It would depend on who welds it - either design with ****ty welds is weak. So next question.............

fietsbob

Hand made custom frames with investment cast Stainless Steel lugs must be built using a silver brazing material that has a lower melting point.

I believe companies like MaxWay Hire a Lot of people to each TIG weld joints, by hand .. They get very good at their job.




...

ramzilla

Butt spliced electroforged gas pipe rubbish trash can department store junk BSO frames are not as strong as elegant hand made high quality light weight Italian lugged frame. Just because.

jvaliensi 

Lugged construction, properly done will last longer than fillet brazed or TIG welded. But in any case they are all good enough when done right.

Trakhak

As someone mentioned earlier in this thread, lugs have often acted as can-opener-like stress risers, causing cracks in a mode not seen with fillet brazing and TIG welding.

ClydeTim

Lugs look strong enough, it's the tubes you got to worry about.

DeRosa.my friend's bike. I believe a 1997 or 98 frame. After 2 years of riding.

Cassave

Hey Jim! Didn't know you where on here.

And I agree, correctly done,lugs yield longer stress paths.
And they always look better.

LiquorLad

Yup. It's easy to spot a high quality Italian bicycle because the paint is flaking off.

rydabent

Lugs with long tapered points would seem to prevent stress points in tubes, even cheaper tubes.