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TIG or braze?

4K views 15 replies 5 participants last post by  rodar y rodar 
#1 ·
I need to add mounting bosses to the fork on my commuter for a lowrider rack. I`d feel better about it if they were brazed, but I`m not very good at brazing (nor is anyone else I know, so nobody to really teach me) so I`m probably going to TIG the bosses into drilled holes- that won`t be any problem. Except that I`m concerned about stressing the metal by welding there. They`re fairly beefy fork legs on a former mtb, but I have no idea what kind of steel. Do I need to worry much about heat stress? Would I be better off brazing the bosses into place at the risk of having the bosses pop out at an inopportune time rather than welding them in and risk the worse possiblility of having my fork legs fold up when I hit a pothole? I know of no bicycle frame specialists in this area, so it`s going to be a DIY job no matter what.
 
#2 ·
Do you have an O/A setup?

If so, you should just do 'em with brass. Practice first on some random piece of scrap, but brass brazing is dead easy (at least for little stuff like brazeons), especially if you've got some TIG experience.

If no O/A setup, my guess is you're probably ok welding them in. But given that you don't know anything much about the material/thickness of the fork blades, it's just going to have to be a gamble on your part, IMO.

-Walt

rodar y rodar said:
I need to add mounting bosses to the fork on my commuter for a lowrider rack. I`d feel better about it if they were brazed, but I`m not very good at brazing (nor is anyone else I know, so nobody to really teach me) so I`m probably going to TIG the bosses into drilled holes- that won`t be any problem. Except that I`m concerned about stressing the metal by welding there. They`re fairly beefy fork legs on a former mtb, but I have no idea what kind of steel. Do I need to worry much about heat stress? Would I be better off brazing the bosses into place at the risk of having the bosses pop out at an inopportune time rather than welding them in and risk the worse possiblility of having my fork legs fold up when I hit a pothole? I know of no bicycle frame specialists in this area, so it`s

going to be a DIY job no matter what.
 
#3 ·
Yes, I have an O/A setup- the added advantage is that I can do it that way at home rather than having to bring my fork into work. It just occured to me that if I drill all the way through each leg and braze both ends of a long boss it would make it a lot stronger than doing it plug style.

Another question, please: From what I`ve read on a few internet sites, I think I`d be better off to get some 1/16 or 3/32 unfluxed rod and paint-on flux instead of the 1/8 coated stuff (all I`ve ever used and all that I currently have available). Do you agree with that? If so, any flux/rod recomendations? Thanks for your response.
 
#5 ·
Use the paste flux!

All-State 1113 flux is good, and you can find it at pretty much any welding supply. Then just buy a pound of their smallest diameter (probably 3/32, sometimes you can find 1/16) low-fuming bronze, and go for it.

If you plead with them, they may even give you just one stick of LFB for free. ;)

-Walt

rodar y rodar said:
Yes, I have an O/A setup- the added advantage is that I can do it that way at home rather than having to bring my fork into work. It just occured to me that if I drill all the way through each leg and braze both ends of a long boss it would make it a lot stronger than doing it plug style.

Another question, please: From what I`ve read on a few internet sites, I think I`d be better off to get some 1/16 or 3/32 unfluxed rod and paint-on flux instead of the 1/8 coated stuff (all I`ve ever used and all that I currently have available). Do you agree with that? If so, any flux/rod recomendations? Thanks for your response.
 
#6 ·
???
Well, I got a pound of low fuming bronze rod and a pound of the All-state 1113 and tried it out with better results than I`ve ever gotten brazing very small stuff with the 1/8 flux coated rod I`m used to, but I`m not sure what it`s supposed to look like. I was expecting the filler to just sink into the seams like when you sweat copper plumbing, but so far all I`ve been able to manage looks like small fillet brazes. Maybe that`s what it`s supposed to look like, I don`t know. I`m also a bit suspicious that the flux may be dried out. I was expecting a consistancy something like axel grease and the stuff in the can I have is more like Playdough, even has a few "crumbs" hanging out on top. For the first practice attempt, I just sorta scraped some flux off the top with an acid brush and wiped it as best I could on the (cold) braze area. The next time I preheated the base metal a little bit first and it seemed to do better. Now I`m thinking that it might work well to heat a little flux first- probably scoop a chunk onto a 1/4" plate and heat from below with a torch. I wish I had a way to get some pictures on here so the folks who know about this stuff could tell me whether or not it looks like it`s supposed to, but I`m having computer/camera problems at home and really can`t do it from work. Hopefully I`ll get it straightened out soon.
 
#7 ·
Add water.

The flux should be the consistency of runny peanut butter, just add some water to it and mix. You should be able to post pictures here (do you have a camera?) and if so I can give you some more feedback.

If the LFB is just piling up on the target, and not being drawn through the slip fit of the boss, you either didn't get any flux in there (likely) or didn't use enough heat (also possible). Try it again with nice runny flux all over the mating surfaces and let us know how it goes...

-Walt

rodar y rodar said:
???
Well, I got a pound of low fuming bronze rod and a pound of the All-state 1113 and tried it out with better results than I`ve ever gotten brazing very small stuff with the 1/8 flux coated rod I`m used to, but I`m not sure what it`s supposed to look like. I was expecting the filler to just sink into the seams like when you sweat copper plumbing, but so far all I`ve been able to manage looks like small fillet brazes. Maybe that`s what it`s supposed to look like, I don`t know. I`m also a bit suspicious that the flux may be dried out. I was expecting a consistancy something like axel grease and the stuff in the can I have is more like Playdough, even has a few "crumbs" hanging out on top. For the first practice attempt, I just sorta scraped some flux off the top with an acid brush and wiped it as best I could on the (cold) braze area. The next time I preheated the base metal a little bit first and it seemed to do better. Now I`m thinking that it might work well to heat a little flux first- probably scoop a chunk onto a 1/4" plate and heat from below with a torch. I wish I had a way to get some pictures on here so the folks who know about this stuff could tell me whether or not it looks like it`s supposed to, but I`m having computer/camera problems at home and really can`t do it from work. Hopefully I`ll get it straightened out soon.
 
#8 ·
Walt said:
The flux should be the consistency of runny peanut butter, just add some water to it and mix.
If the LFB is just piling up on the target, and not being drawn through the slip fit of the boss, you either didn't get any flux in there (likely) or didn't use enough heat (also possible). Try it again with nice runny flux all over the mating surfaces and let us know how it goes...-Walt
YEAH! Now we`re cooking! Walt and Derek, thanks a million for the advice- like I said, nobody I know around here really brazes much, so I don`t have a local resource to hit up. Here`s a play by play on what happened with the "peanut butter" flux:
The first two trials came out better, but I still thought I might have too much flux (the brush got all goobered up because I used it to mix when I thinned my Playdough). For the next one, I used a piece of match book to spread just the minimum I could without leaving any bare spots- the brazes looked like yesterday`s. So I started wondering what happens with too much flux. To experiment, I gooped on what looked to me like WAY too much and dang if it didn`t turn out good! The only problem I noticed was that it was really hard to see where the LFB was flowing (turned out to be flowing everywhere, but I guess it`d sand off if I were doing a real piece.) For the last two I split the difference and I think I`m on target. My practice pieces were hollow plugs dropped into holes in a tube about the same size as my fork legs. When I finished, I split the tube with a bandsaw and could see a nice bead of bronze around all the plugs (inside view) except the one that I didn`t put enough flux on. It does take more heat than I thought it would to melt the 1/16 rod, but I guess it still isn`t bad. It`s melting with the base hotter than dull red, but not quite to cherry. Sorry, that`s the only way I know to judge temp of nonmolten steel.

The problem with pics is another story. My wife`s old computer is full to the gills and won`t take any more pics at all. We just bought a new one to replace it and are still working out the bugs to get it online and to interface with our little digital camera. Also, we`re going from Windows to Mac, so it may take us a while to get through the learning curve. We`ll get it somehow, though- I`ll be sure to post a picture of my forks when I get them brazed up.

One more: I usually use a #4 lens for all O/A stuff but it seems too dark for this little stuff. I`ve been working just with my clear saftey glasses today and I think it`s a little bright for that because I see spots for a while after each shot. What do you guys do for your eyes?
 
#10 ·
I just use a pair of sunglasses (with UV protection). I find it a little bright when I use just clear lenses as well, but actual brazing/welding lenses tend to be too dark.

It's almost impossible to have too much flux, btw. Glad things are working for ya!

-Walt

rodar y rodar said:
One more: I usually use a #4 lens for all O/A stuff but it seems too dark for this little stuff. I`ve been working just with my clear saftey glasses today and I think it`s a little bright for that because I see spots for a while after each shot. What do you guys do for your eyes?
 
#12 · (Edited)
rodar y rodar said:
One more: I usually use a #4 lens for all O/A stuff but it seems too dark for this little stuff. I`ve been working just with my clear saftey glasses today and I think it`s a little bright for that because I see spots for a while after each shot. What do you guys do for your eyes?
I'm with Walt, I usually just use my sunglasses (which have UV protection) but I've also brazed with clear glasses (taking care not to look at the flame).

Also, you really can't use too much flux. When I started on my first frame I was using a minimal amount because I was putting too much heat into the joint and burning the flux. Which leads to a big pain trying to get it off. But I slather quite a bit and usually a couple of inches surrounding the joint. The stuff comes off easy in hot water (unless you burn it, see above).

Keep trying.

-Derek
 
#13 ·
Uh, not really

This is a gross simplification. Both methods are more than _strong enough_ to build a safe bike frame, and that's what matters. And in many cases, a brazed joint is *stronger*, because the metal must be heated less and stress risers are further from the joint itself (especially with lugged work).

Keep in mind, I'm a TIG guy myself. I just don't like to see one or another method bashed for being "weaker" when all of them are way beyond stronger than you'll ever need, assuming you do a good job.

-Walt

kuksul08 said:
Brazing isn't as strong as TIG but it's more likely to weaken surrounding
metal if it gets too hot. Just do whichever is easier and work slowly
 
#14 ·
I did it!

In the end I brazed the upper ones into the fork legs, then welded another set onto the top sides of the dropouts (can`t be much stress at that point). I took a long time practicing, making jigs, then waiting for an opportuity and in the mean time I changed my mind about the lowrider rack and decided to go with something like I saw on antbike. Let`s see if I can get that pic to load. I`ll put up pics of mine in the morning- we have the new computer up and running.
 
#16 ·
Well, I managed to get one of them pretty much cleaned up. I hoped to have them both clean so I could shoot a little primer on them because it looks like rain but it`s taking longer than I thought and I`m ready for bed. Maybe tomorrow. Thanks for the help, Derek and Walt.
 

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