I suck at fillet brazing, but I don't want to! How to get the bronze flowing

[suravida]

Hi there, I have been reading this wonderful forum for quite some time now, but I need a bit of guidance... Beware of long story from complete novice/noob (But who just realised he loves working with metal, bikes and his hands)

So I had the idea to build a bike. I have been working on a drawing for the perfect Long Travel HardTail 29er for 3 years and after losing my job as architect decided this would be the time to build my own bike. :-)
At first I bought this tiny brazing set with cannisters of O2 and Propane/butane. Even built myself a racebike using some plain gauge tubing and Sif101. However, I fiddled so much with this frame that I decided it would be best scrapped and that my next attempt would be better.
So, I went to Bart Veuger from Windcycleworks for a morning's crash course using his Oxi/Ace setup and did a quite nice testbraze and got fairly confident I could go on myself. With his setup I could easily heat up a small spot on the tubes, apply some molten bronze and get out. Then moving the heat around the edges to thin the bronze and finally adding layers to create a nice fillet.
Yesterday I bought myself a oxi-propane setup (10l oxi, 5kg propane, Gloor handle with nr2 tip) Acetylene was way too expensive, and I read here that propane might be just as good, although requiring a slightly different technique. So now I am practising my ass off but I keep on running into the same issue.....
The initial heating of the tubes and spotheating the tubes to apply a dab of bronze works fine. (slightly slower than with OA, but not a lot). The thinning already gets a bit more tricky because I need to add quite a bit of heat to let the bronze flow around the tube. Here the tubes are getting redhot already. But in the end I do have a thin seam between the tubes, so it works.

However, when I then continue to make a small "dam" of bronze (while the piece is under 45 angle) I first need to apply a lot of heat to get the bronze on top of the thinned seam to flow. Tubes next to the bronze are now redhot and the bronze only just melts very locally. If I add more heat (to start to move the fillet around the tube) the bigger tube seems to reject the bronze, almost like a droplet of water on a leaf. The bronze sticks to the smaller tube but doesn't go everywhere to the other tube. I tried gravity, heat, pushing with the rod, but with no or little effect. Sometimes, when the tube is almost yellow hot, it runs a little, but then small holes don't close or it stops running a bit further.
I realise I need to practise a lot more, but I feel I am overlooking something here or using the wrong technique, and it's pissing me off. I tried different tubes, different pressures in both tanks, different flames and intensities, I degrease the tubes, sand them thoroughly inside and out and apply a thin even coat of Cycledesign flux.
Here is picture of my last failed attempt, which looks even worse since I tried to heat it way too much and bronze started dripping. But still not attaching to the damn tube! You can see the rounded edges of the bronze, this where it stopped flowing onto the tube. (like the water droplet)



TL:DR > How do get the bronze to flow nicely and attach to both tubes instead of getting rejected by parts of the tube. I would be so happy if someone could have some advice on this, I really want to continue building my bike. :-)

[Eric Estlund]

Way too hot, and much too localized. You are likley spot boiling the brass and overheating the steel causing an unstable joint with virtually no chance of wet out. I'm not sure what you are using for flux, but that looks cooked, too.

In my smoked out there is a video showing real time preheating and brazing of a joint. Take a look- my guess is that you are rushing the pre-heat and then jumping in with too much flame (or a small flame for far too long) on a single point. I use O/A, but the brass doesn't care what chemicals are used to get the tube hot, it just cares about the temperature and location.

[suravida]

I am using the Cycle Design low fuming bronze flux. I am taking some time to gently heat the tubes, but it might be that I am using to big of a flame. I am using a propane tip: Gloor Lilliput nr 2 1-2mm.

For the preheat I know stop when the steel gets reddish when I hold the flame in one spot for a second (or a bit shorter). I don't think I should have the whole piece glowing red right?

Here a photo from the last test, just thinning. I tried to preheat slowly and very shortly heat from really close (1cm) to melt the bronze. Is this still too hot?

[suravida]

I guess this is the video you mentioned? Eric Estlund - Real time stem brazing | Facebook

And going through your Smoked Out thread only makes me wanna braze more, very nice work!

[Eric Estlund]

There are pros and cons to tinning. At this stage, skip that step. The tinned bridge acts to sink heat between the tubes, and you need to get the bronze to be liquid to get the fillet to flow into it properly. Those are all more advanced steps. Once things are tacked enough to hold the work, try to get your preheat to flow right into your fillet brazing sequences, or as much as you can at this stage. If it's too hot, let it cool, and if you feel you have to force it, slow down and let things come up to temp.

Mess around with your settings, speed, etc. DO NOT BUILD A BIKE. Run a bunch of practice tubes and joints. You want to isolate this (life dependent) skill before building. After you get a bucket post back with some of the results, good, bad, and the stuff in between.

PS- Please add your full name to your signature or posts in the Frame Building section, per the forum rules. Thanks!

[suravida]

Don't worry, I will not build bike any time soon. I'll first destroy a couple of meters of tubing, messing around with the settings and timing. Thanks for now! If I have some progress I'll post it here.

[Amaro Bikes]

Hi Suravida

Please add your first and last names to your profile or signature, as indicated in the postin guidelines, so we all know who we are

Thanks

P.D. About your question there's nothing much less to add to Eric's masterclass

[suravida]

I added my first and last name to my profile last night. Is that not the place to do it?

- Michiel Burgerhout

[Eric Estlund]

Thant s a great start. In your profile page you have the option for a signature line. For the Frame Building section we ask that it be displayed in the signature line.

[suravida]

OK, changed that too. Concerning the brazing: Gotten some great suggestions (also via PM) and slowly getting a better grasp on what I am doing. Also gotten a smaller tip (0.5-1mm instead of 1-2mm) which helps greatly in not overheating the tubes. Once I create something vaguely resembling the work by the masters here, I will post it.

[suravida]

SO..took some time but I finally built a bike. Fillets may not have the most beautifull ones, but I am quite confident that they will hold up. Rode 2 cols in the French Pyrenees with it, had some hard hits on the bad roads going down and it didn't show any weaknesses. I did however got the wrong fork for my geometry (to short and steep) so in the future I'll build one myself. Now first I start on the Long Travel Hardtail 29er :-) (finally after all those years)



Designed a watercut brakemount with name of the bike in it (HvH, stands for Hoek van Holland, the place I ride to on this bike)


Love working with silversolder and making these details


Paint makes all the difference! Made the seatclamp out of a bit of spare tube and the eyelets I cut off of the dropouts, very pleased with the detail


Thanks for all the help so far! I couldn't have built this bike without it and will probably come for some more advice later on. And when I finish paint on this one and get some proper photo's I will also post them.

[suravida]

And to finish this topic the pictures I took of the finished product: