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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 3:53 pm 
rBoTM Winner
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Brazing is done at a lower temperature than welding so the tube can be thinner at the juncture without being compromised. (at least this is true for lugged construction) If the same is true for filet brazing then this could explain the use of said construction on higher end frames as it would be an expensive tubeset and labor intensive.


Steven


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 3:55 pm 
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LOL, I've been pretty much convinced that logic and bicycles have no relation or shared DNA. I live in a town full of hills and all the silly kids build fixies! AAAAUUUUUUGGGHHHHHHHHHHH!!!!!!

For reference (they are not too common, even over here), here is my Santana:

Image


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 3:59 pm 
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lewisfoto wrote:
Brazing is done at a lower temperature than welding so the tube can be thinner at the juncture without being compromised. (at least this is true for lugged construction) If the same is true for filet brazing then this could explain the use of said construction on higher end frames as it would be an expensive tubeset and labor intensive.


Steven

Its done 1100+ degrees C lower than tig welding, so there's less potential for tube erosion or distortion, so you can use thinner tube or a less skilled workforce. Depends where in the world you are as to which side of the coin most likely applies.


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 4:10 pm 
rBoTM Winner
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Point well taken, just because something is brazed does not make it well constructed, Firenze gl5000 anyone.


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 4:31 pm 
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Large fillets can make for a stiffer joint - but although brazing's potentially less stressful to the tubing, the extra time sometimes spent on large fillets can weaken the steel (or so I've read)


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 5:21 pm 
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Originally the custom builder went for fillets because the lug were road angles and it was hard to build a bike with the right bb height and head angle. you can tweak and road like a degree or two but then you are out of luck. Fillet lets you make any angle and its pretty quick to do in comparison to lugs.(read the Paterek manaul http://www.timpaterek.com/tpmanual.htm) its the finishing that take longer than making the dam thing.

As for strength and weight. if you make a close fit joint do that the tube miters shows a perfect fit you can use very little rod and make small fillets. like on http://www.enigmabikes.com small fillets and no real weight gain. If the tube thickness is 1.0mm you can do a fillet that is 4mm in radius and still get full strength so not much more that a tig weld. Smaller if you use a 5% nickle rod. problem with small fillet is they are very hard to finish. Overbury used to use dyna-file then by hand to finish their fillets so it makes sense to make them big so you can get the tool in to file them. Obviously back in the day there was no cad based finite element testing software, so off road probably best to make them a bit bigger right?. big fillets don't damage the tube strength through heat damage but more often but warping the tubes. you can use this to tweak the angles as you build so if you add more fillet to the side of the join when it cools it pulls in that direction.

Older tubes sets were more sensitive to heat and tig welding was often not a strong as fillet brazing. This is not true now, some of the Columbus/ Reynolds tubes lose no strength when welded or even get harder (niobium additive).

Tig welding became the way just out of speed, no fluxing, not pre heating, no flux clean up, no file to finish. but where the fun in that? to me it done matter how its built as long its build well and there some craft put into it. so an 20 year old British built bike with fillets still makes me smile. Hope you find one.


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 5:28 pm 
retrobike rider / Gold Trader
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What I find odd is that in the world of vintage motorcycle frames, its called bronze welding rather than fillet brazing. A lugged frame would referred to as brazed, whereas one without lugs is bronze welded. Same filler material, different process.

I realise that its not really welding, but that's what its called in that application. I have several 1960's motocross bikes using Reynolds 531, bronze welded (or fillet brazed if you prefer). The one in my avatar is one.

I believe the main reason all most old frames are brazed is that the tubes made in that period would lose their strength if welded. As soon as better steels were available, which could be TIG welded without losing their strength, frames could be made with equivalent strength as previously, but lighter due to lack of lugs or great blobs of braze everywhere. I hope this makes sense!


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 5:34 pm 
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andyz wrote:

I believe the main reason all most old frames are brazed is that the tubes made in that period would lose their strength if welded. As soon as better steels were available, which could be TIG welded without losing their strength, frames could be made with equivalent strength as previously, but lighter due to lack of lugs or great blobs of braze everywhere. I hope this makes sense!


the tubes have got better but so have the TIG welders digital control, pulse ramping cycles etc.


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 5:40 pm 
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biglev wrote:
Originally the custom builder went for fillets because the lug were road angles and it was hard to build a bike with the right bb height and head angle. you can tweak and road like a degree or two but then you are out of luck. Fillet lets you make any angle and its pretty quick to do in comparison to lugs.(read the Paterek manaul http://www.timpaterek.com/tpmanual.htm) its the finishing that take longer than making the dam thing.

As for strength and weight. if you make a close fit joint do that the tube miters shows a perfect fit you can use very little rod and make small fillets. like on http://www.enigmabikes.com small fillets and no real weight gain. If the tube thickness is 1.0mm you can do a fillet that is 4mm in radius and still get full strength so not much more that a tig weld. Smaller if you use a 5% nickle rod. problem with small fillet is they are very hard to finish. Overbury used to use dyna-file then by hand to finish their fillets so it makes sense to make them big so you can get the tool in to file them. Obviously back in the day there was no cad based finite element testing software, so off road probably best to make them a bit bigger right?. big fillets don't damage the tube strength through heat damage but more often but warping the tubes. you can use this to tweak the angles as you build so if you add more fillet to the side of the join when it cools it pulls in that direction.

Older tubes sets were more sensitive to heat and tig welding was often not a strong as fillet brazing. This is not true now, some of the Columbus/ Reynolds tubes lose no strength when welded or even get harder (niobium additive).

Tig welding became the way just out of speed, no fluxing, not pre heating, no flux clean up, no file to finish. but where the fun in that? to me it done matter how its built as long its build well and there some craft put into it. so an 20 year old British built bike with fillets still makes me smile. Hope you find one.


Nicely put and very informative, thanks for posting.


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 Post subject: Re: Fillet brazed frames
PostPosted: Fri May 24, 2013 5:48 pm 
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there was also a lot of prejudice (in the UK at least) against TIG welding in the early days, as it was seen as the cheap and inferior realm of US mass-producers. :roll:


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