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Lugs as strong as welds?

Old 07-20-21, 01:44 PM
  #51  
tungsten
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Originally Posted by Scooby Snax View Post
the tig process weakens the material around the joint.
That's why tubes are butted and aluminium heat treated.

Originally Posted by rydabent View Post
Then came computers and robot welders.
I spent 25 yrs in the fabrication plant at RMB and never were any of the offshore produced frames we brought in welded by "robots". Unless they were the human kind.

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Old 07-20-21, 01:55 PM
  #52  
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Originally Posted by Andrew R Stewart View Post
There are millions of lugged bikes that were machine brazed. The machine provided heat and filler came before the current popularity of welded joints. Additionally some high volume production frames used tack welds between the lugs and the tubes to hold the structure while the machine brazings were done, much like pins can hold a main triangle before brazing.
I know some British builders used to "pin" the tubes in place in the lugs and then fire them in a kiln.
What is this "machine brazing" you speak of?
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Old 07-20-21, 08:50 PM
  #53  
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Originally Posted by tungsten View Post
I know some British builders used to "pin" the tubes in place in the lugs and then fire them in a kiln.
What is this "machine brazing" you speak of?
It's not complicated to get brass filler rings that fit within the joint during prep. Alignment can be handled by a few methods including pins or jigging. Torch application stations with timed cycles to melt/flow out the insert. If the process is done well there's very little clean up and less skilled people load tubes and filler inserts instead of handling the torches. IIRC Peugeot's lugless early 1980s frames were done this way as many others too. Andy
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Old 07-21-21, 12:54 AM
  #54  
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I would think nobody will ever know which is stronger.

My guess is to prove it a test would have to be done with maybe 10 welded frames and 10 lugged frames- all other variables held constant. And the frames would be put in a machine that simulates a very strong rider grinding it out. And run the machine until the frames break.

I bet thatís never going to happen. And I bet both ways are strong enough.

I think lugs are cool looking.
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Old 07-21-21, 06:53 AM
  #55  
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This entire discussion is interesting but moot. The overwhelming majority of new bikes are carbon fiber, welded aluminum, welded steel or, more rarely, welded Ti. The lugged steel frame has been relegated to the speciality boutique custom frame builder and made in very limited numbers at prohibitively high cost for most buyers.
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Old 07-21-21, 07:34 AM
  #56  
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So it isn't moot for someone who's looking at getting a nice specialty frame, then.

Personally, I wouldn't mind any one of these:







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Old 07-21-21, 05:26 PM
  #57  
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Originally Posted by hydrocarbon View Post
So it isn't moot for someone who's looking at getting a nice specialty frame, then.

Personally, I wouldn't mind any one of these:
That is exactly my point. Those lugged frames you show are all expensive, boutique, hand made, one-of-a-kind frames and that's the only way to get a new lugged frame these days.
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Old 07-21-21, 07:49 PM
  #58  
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Originally Posted by tungsten View Post
I know some British builders used to "pin" the tubes in place in the lugs and then fire them in a kiln. What is this "machine brazing" you speak of?
At Trek in the mid 80s, we used torch-free electromagnetic induction to heat the joints, and automated wire feeds to feed brass into the hot joints in combination with pre-placed brass "bombs" inside the tubes.

A lot of money was invested in this project, which became superfluous within a couple years as non-ferrous aluminum and carbon fiber frames came to dominate the market.
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Old 07-21-21, 08:16 PM
  #59  
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Originally Posted by shahidbashir92 View Post
In the case of bike frame lugs, the brazing is under sheer forces only - as the tubes are inserted into the lug. The joint will be as strong as the metal of which the lug is made. If you used the same brazing material in place of a weld, it would fail - because its now subject to variety of forces (pulling apart and sheer).
<pedant mode>
*shear*
</pedant mode>
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Old 07-22-21, 01:40 PM
  #60  
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Originally Posted by shahidbashir92 View Post
...because its now subject to variety of forces (pulling apart and sheer).
Welcome to the forum and please forgive us for being pedantic, it is sometimes difficult for myself and others to not to care too much about minor details in very narrow cycling subject matter, Your points on shear are spot on. That said, frame tubing loading is mostly in compression, bending or torsion with a couple notable exceptions.
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Old 07-22-21, 03:04 PM
  #61  
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But you must admit that todays welded frames look like the cheap welded frames of the pre 80s when good bikes had lugs.
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