Help with bazing required!

Hi everyone,

I recently bought an oxy-acetylene rig and ive been doing some brazing on a tall bike thing, luckily it doesnt have to look good because they look like trash! I have been taught by a framebuilder but used oxy-propane then. Now trying to teach myself but it doesnt go as well. Somehow at the same time im burning my flux but also the tubes aren’t hot enough and the bronze does not melt properly. When i apply more heat to the tubes the flux burns. I feel like the window of flux not burning and the bronze melting is really really tight. Any tips?


There’s definite progress. Torch size and settings might be an issue. It’s important to be able to identify a good neutral flame and adjust quickly to achieve one. Paul Brodie videos on youtube are very helpful.

Start with very clean metal. Sand to shiny with 80 grit, and wipe down with alcohol or something. I wash everything with dawn soap.

Dipping the rod in flux and making bronze icicles/trees, as described in the Brodie video, is very helpful for learning about freezing/thawing.

I use shade 3 glasses. I am giving up some protection for clarity.

Probably wrong flux.



Couple questions -

Torch tip size?
Regulator pressure?
Brass size?
Flux type?

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Hey walt, my flux is the one reccomended with the rod, its universal brazing flux for steel/bronze/copper

Tip is smallest available for my torch, size 0.
Cone is medium sized, around 6 mm i think
Brass is 2mm
Flux is universal brazing flux

It’s frustrating because I feel like the first time I did brazing, which was when I did a framebuilding course I was doing a better job at it then I am doing right now, maybe that was because of the constant eye of an experienced builder guiding me but I feel like something else is off. I’ll add a picture of my brazing work from the first day.

anyway, I did sand but Didn’t clean with alcohol, ill try that the next time.
I’ve watched Brodies video’s religiously over the past few months and they definitely helped me to understand more clearly. it’s frustrating that I feel like i’m doing the same thing he is but it is not working out :slight_smile:

Your torch tip is likely too small. With too small of a tip, the flux burns but the brass and base metal does not get hot enough. I use a #1 or #3 for all my frame joints and a #00 for brazeons and racks.

If you can, try and track down some Gasflux c-04 rod and gasflux type-b flux. I was using some random stuff from the welding shop before I was building frames, and holy moly the gasflux brand of goods is a lot easier to work with.


Yes get some gasflux paste and try that.



hey there,
The tip thing is a very good suggestion, ill try with a slightly bigger one tomorrow, maybe that will help. As for the flux and bronze, I am using different stuff because I live in europe and I couldnt find anything from Gasflux or SIF, but this is supposidly bronze made for the bike industry too. maybe If I can find some gasflux ill try it out.

Love your bikes btw, I would like to get to the point where I leave fillets raw but at this point it would just look like shit :slight_smile:

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I mean, what jumps out at me is the burned flux. That’s super hard to do with flux intended for bronze. Like, almost impossible in my experience.

The tip size isn’t ideal but it can still work fine so imo it’s the flux.


strange, but It is the experience I also had when doing it the first time with ‘proper’ flux. The metal would get sprakling red far before the flux would burn

Who said you can’t leave shitty looking fillets raw? Here’s my second frame ever, I rode these bubblegum fillets for a long time haha


Well i guess for my next frame ill leave them as is i guess, hope to build a fork too but that seems just as tricky as the frame

I also suggest finding better flux. Your fillets are lumpy because you might be pointing the flame at the rod and not the tubes. Then the rod melts and plops on the colder tubes, where it solidifies.

Make sure you know how to make a neutral flame.

A bigger tip is a good idea. You want to point your flame really close (2-3mm) at one spot and dip your rod there. If you’re waving your flame everywhere trying to heat up enough area it’s going to be messy.

I’d also suggest finding a smaller diameter rod. In the US we typically use a 1/16" or 1.6mm rod. A thicker rod is a little harder to use since it takes longer to melt.

This sounds weird, but I’d suggest watching TIG welding videos to learn to fillet braze. The concept is the same. Concentrate the heat in one area, when it’s hot enough dip the rod, then remove the heat for a second or two until the puddle solidifies, then repeat.


Ill try to find some different flux, as stated above in another reply I got the gist of it the first time I did some brazing, but then I didn’t have to worry about overheating so much. ill get back to you all when I have tried a bigger tip, when that doesnt work ill see if i can get some other flux


You need some of the unctuous gasflux type B, or equivalent SIF stuff :slight_smile: When I first started brazing I bought the Cycle Design USA bronze rod and flux and really struggled with it. I bet I could get on better with it now, but I had a much better experience with the Gasflux stuff, the flux really sticks around and forms a nice goo.

Oh and Brodie gives excellent advice on brazing, but remember he’s using a gas fluxer, so when he says ‘I don’t understand these other builders gooping on the flux’ keep that in mind.


Yeah ive been watching brodie religiously but his opinions on flux are based on his obvious skill with a torch and his gasfluxer, nevertheless, a lot of valuable information

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