The custom builders you come across always seem to either braze or use lugs, whereas steel frames built in Taiwan are welded. Why don't the custom boys weld? Surely it's lighter and stronger isn't it?
Because it looks nicer.
In fact, it looks very, very nice indeed. And if you're gonna get a custom frame, looks are very important.
And I believe that fillet brazing is actually stronger then the metal it joins, which is more than strong enough.
Clue's in the name, if you want your CUSTOM built bike to be welded, I imagine they'd be more than happy to do that for you, no?
But they only ever mention brazing and lugs, never welding.
[shrugs/]
Right
lighter and stronger maybe but no where near as cool. also lugs can be undone with some degree of success so its like a tailored suit that can be changed in 20 years to re-fit the owner.
brazing is oldschool too, probably pre-dates welding and so its more of a traditional thing, much like custom frames.
Lugs must be easier too.
i'm not sure if they are easier, well maybe easy to pick up but hard to master. i've welded and i've brazed, i made an equal mess of both
I think the repairability is the main justification...and it looks prettier.
Apparently if you're welding very thin high-end steel tubing, it's easy to melt a hole right through it.
IF weld ;0)
we weld, that'll be our main method once we launch. CEN to get our heads around first. We plan to follow with fillet/lugwork, but Matt's putting his time into TIG. Sounds like that's what some people might like....
Welding tubing that thin is an art. I suspect it is also because its a damn sight easier to braze tubing together in a small workshop than it is to learn to make repeatable and ultimately removable/modifiable solution than it is to correctly weld up sub-mm tubing without it warping and blowing through etc, and brazing can be "neater". Plus if you're using the lugged method you can cut the metalwork to size and then simply assemble and braze, with welding you need to spend more time clamping and ensuring it's all lined up.
IMO.
Welding creates more heat as you are actually melting the metals together whereas the brass in brazing acts more like a glue.
The more heat you put into the frame the the higher the chance of distortion.
welding creates a larger 'heat affected zone' actually changing the crystaline structure of the material, creating larger crystals, which is more likely to fatigue and fracture I believe.
This is also why aluminium frames have to be heat treated to normalise them.
Because brazing looks like this,
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Which looks nice. Plus you can take a brazed frame to bits & alter it if you so desire. Like if your arms grow longer or something.
tig welding thin tubes is quite tricky, somebody who can braze lugs can't just pick up a tig torch and expect to tig weld. plus the mitering has to be spot on and not hidden under fillet brazing or lugs.
brian rourke makes some lovely tigged frames from oversize shaped steel.
as do pegoretti and scapin
So those Taiwanese geezers must be bloody good then.
good. but a lot of the welding (on steel) doesn't look as good as on some custom frames (comparing a rourke, duell, scapin and pegoretti that i have seen close up with off the peg Taiwanese built MTB's) doesn't mean they are not properly welded just not as neat as they could be.
Well cutting tubes isn't rocket science really, that's what holesaws are for...
The weird thing is pretty welds arent always that strong!!!
Im pretty sure that the only thing I can add is that because of the heat effected area a welded frame needs to be heat treated to be reliable, this is quite an expensive process. In many respects when making custom frames fillet brazed is better. Fillet brazed is not governed by the constraints of the lugs angles, however nice a lugged bike looks; especially some of our framebuilders personal jobs.
I spoke to a frame building friend of mine and his word is that it is mainly aesthetic. He says it is no more difficult to braze than to weld but for the frame builder the process of brazing is better as you don't have to contort yourself to get the torch all around the most remote parts of the join. After all he told me why have a custom frame welded so it looks like it was made in Taiwan?
Don't lugs pre-determine the geometry? Or are the lugs custom made too?
Lugs can be custom filed to whatever the builder requires.
It's pretty easy to blast a hole straight through a thin tube brazing as well as TIG welding. I think it's primarily a fashion/difference thing. THat said, there are a number of production frames which still use lugs, as well as a number of custom builders which TIG weld (Strong, Seven, IF, Goodrich, Crisp + basically anyone who does Ti, and a whole host of others).
Don't lugs pre-determine the geometry? Or are the lugs custom made too?
There is a variation of +/- 1 degree within any given lug, and lugsets often have a couple of variants of the main tube junctions so as to allow quite a wide range. That said, yes it can be constraining in terms of geometry to design/build a frame with lugs, but not to the extent it won't be custom. Yes, it possible to fabricate lugs, but to actually cast your own lugs which will be sufficiently strong is a very involved process for a one-off frame. Often the route taken is to adapt existing lugs, or to make something which looks like a lug by brazing together tubing then cutting. This is done purely for aesthetic reasons though.
"why have a custom frame welded so it looks like it was made in Taiwan? "
tig welding doesn't have to look like it is welded in taiwan. the welding by the builders i named above have very neat welds, it's also lighter than brazing or lugs.
You can also smooth welds down like Cannondale frames, so this excuse of it looking better doesn't hold.
Lugs do determine frame angles and filing them is used to make them look pretty not to alter the angles. There are lug sets which allow a small slope on the top tube ( usually 6 degrees) but with a bit of ingenuity, in this case by turning a lug upside down, amazing things can be done:- [url= http://forums.mtbr.com/showthread.php?t=507850&highlight=curved+top+tube ]lugged cruiser[/url]
euchhh I hate cruisers! 😀