I’m building my first bike frame and I need some help. I got everything tacked and main tubed fully brazed. These turned out good (well as good as I expected for frame 1). I’m really struggling with a few areas.
- I am using a 3d printed yoke and I cannot seem to get anything to melt onto the yoke. I have heated and heated the bb and the yoke but every time I add filler it just balls up. Really afraid of adding more heat. On the cs side of the yoke filler melted and filled the slot just fine.
- I added a few 4130 braces and these are balling up too. I know I’m struggling with consistent flame. I’ll watch the Brodie video and sometimes it’s perfect neutral and others it takes me 10 tries to get it back.
- Is there any reason my flux on these secondary joints is burning black and gumming up to a sticky substance. Flux was fine on the original joints but now it’s acting like glue and gets super nasty.
I know it’s hard without any pictures, I’ll try to add some today.
Any info would be awesome though.
Are you using bronze or silver rods? The 3D print will be stainless steel and bronze doesn’t like to stick to stainless.
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I was using bronze. I have some silver that should be showing up tomorrow. Thanks for the info.
I was actually just enjoying my coffee while drooling over all of your pictures when you responded. Your work is beautiful, serious inspiration.
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Be really careful with the heat. Silver also uses a different flux, which also helps you know when you’re at the right temperature. Its very possible to overheat stainless and will make it practically impossible to braze afterwards.
Definitely speaking from my own challenges here 
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Oh yeah, to add to Tom’s comments. You’ll need to make sure everything is clean and give the surface a quick touch up with scotch bright or sand paper. The stainless forms an oxide in air and needs to be removed before brazing. You’ll have a couple hours window to work in so no rush.
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I’ll go further and say no one should be using stainless at all until their brazing skillz are top-notch. Stainless is so unforgiving, it’s a common source of frustration and failure for beginners. Actually for experienced hands too, if you aren’t bringing your A game in every way. Cleanliness, fit-up, prep, flux quality, flame size, fuel mix, tip cleanliness and most important of all, ability to soak in a lot of heat without localized hot spots or using up your flux. Once silver flux turns black, it’s not longer working and you musty stop, take everything apart, clean back to shiny steel and start over.
You need to know that SS gets an oxide film on it that prevents proper wetting and bond with the silver. This happens rapidly, so you should sand everything to shiny right before brazing. Not the day before, maybe not even 2 hours before. I don’t know exactly how quickly it grows back, but I try not to give it any time at all.
Someone here who makes SS bikes can probably chime in with real advice on how long you can wait to braze after sanding.
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I was told a couple hours but in practice I will sand the areas taking silver immediately before I’m applying flux and fitting stuff together.
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A quote I try to live by: when something goes wrong, no one ever says “yeah, I probably cleaned that too much”
Whenever I work with Stainless (not silver), I clean right before fluxing and brazing. I try to stay away from it except little washers for dropout faces or stress relief holes.
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Really good advice. Thanks
I did not realize the 3d printed yoke I purchased was stainless.
Question, I know nothing about 3d printing. Are all 3d printed parts stainless?
Usually. Yes. The most common materials for waht we are doing will be 316 or 17-4 stainless. There are a range of other materials available but are not appropriate for steel bicycle frames.
Obviously there is aluminium and Titanium as well.
Thank you guys for all of the info.
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The fact that you are having problems with the 4130 braces makes me think there are more fundamental problems, so the yoke was never going to work. I would step back and do some practice joints. Are you sure the flux and filler are compatible? But if you have lfb balling up, that just means you aren’t letting things get up to temp. You probably have to separately heat the lfb a little, but not enough for it to ball up. It still should be melted by the steel.
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Without knowing what sort of instruction you have had or whether you have done any brazing practice, it’s hard to advise - especially without pictures. As a relatively experienced builder, I can say that my foray into 3-D printed stainless parts was frustrating. I have no issues with chromoly, whether bronze or silver, but the 3DP parts were a challenge. I would not recommend using them on your first frame unless you’re comfortable with a joint failure after the first few rides.
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Thanks for the info. Just the bit I’ve learned I agree the 3dp parts are very unforgiving and hard. I won’t be sad if this breaks. All part of the learning curve!