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Thread: Brazing redo?

  1. #1
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    Brazing redo?

    I fired up my first career (amateur) braze this afternoon, and I would say that it didn't go too well. I'm particularly concerned about a few visible gaps in the fit. I tried to show one of the gaps in the underside of the lug.

    http://www.flickr.com/photos/1483147...n/photostream/

    Feel free to let me know if it's as bad as I think it is.

    I'm unsure of what to do next. Is this a complete take apart and rebraze? Or can I reflux and braze the small gap or two that exists?




    Any thoughts would be much appreciated.

  2. #2
    Andrew R Stewart Andrew R Stewart's Avatar
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    Not too bad a first effort and with practice you'll do much better soon. It looks like you used Silver. I like to start my students on brass/bronze. it's cheaper, learning heat control can be more critical (as things are hotter overall), the slower flow of brass/bronze makes it easier to "keep up" with what's going on, it's less critical WRT cleaning and prep work and it's more forgiving of poor fit up.

    Your joint looks like the end with the gap had either not been fitted well to start with or the lug end lifted up during brazing. Once the gap grows to a large enough amount no amount of filling attempts will do to fill the gap. You could have tapped down/squeezed down the lug end to close up the gap during brazing, not easy for the newbie though. When I've had a poor fit up (often due to the joint angle being off the lug's angle) I'll sometimes use a hose clamp to hold down the lug tip during the brazing of the majority of the lug, then remove the hose clamp before I flow out to the tip. Really the best advice is to prep and fit the lug/joint better to begin with.

    You have left a number of areas on the shoreline with globs of filler remaining. Perhaps from trying to over add filler to fill the gap just mentioned. But not a pretty result and will leave you with a lot of filing to clean up. You can use the flame to help even out the globs after flowing the lug fully. Bring the torch in close to the shoreline and melt just the filler exposed past the shoreline. It will spread out and try to even the globs with the lesser globbed adjacent areas near by. By running the flame around the shorelines the globs melt in and flow out. Sometimes the flux hides the shoreline detail, using the filler rod to rub up against the shoreline can help push flux out of the way so you can see better, but do this at a temp that the flux is still liquid but not hot enough to have the filler rod melt. If there's too much filler you can draw it away from the shoreline and to an area of tube that's going to be cut off or easily gotten at with a file.

    I don't see evidence of overheating and the areas that are filled look to be fully filled. Again a good first. Cut this open and confirm the internal fill rate then have another go. Andy.

  3. #3
    Randomhead
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    Quote Originally Posted by Andrew R Stewart View Post
    I don't see evidence of overheating and the areas that are filled look to be fully filled. Again a good first. Cut this open and confirm the internal fill rate then have another go. Andy.
    I agree with everything that Andy said, but this is the most important part. Looks like you are pretty close. You are going to hate yourself if you don't get your shorelines cleaner with the torch. Since you seem to have heat control down fairly well, you should be able to have time to see where there are gobs of filler and move them somewhere that they will not require you to file them.

    Cut it up and see how you did with penetration. You will eventually know if you got full penetration, but until then, it's good to check occasionally.

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    Andy and unterhausen, thanks for both of your insights. I followed this board for a while in the lead up to beginning my build, and I came across your posts often while doing so. It's a real pleasure, and reassurance, to hear from you guys.

    For what it's worth Andy, you were spot on in terms of the speed things happened with the silver filler. Owing to advice I got on this board, I purchased 0.058" tubes from Spruce, cut them up, and practiced on them as "lugs". All in all, it was great advice and practice. However, the much thinner real lugs came to heat in what felt like no time and the silver was really moving. I can see how a slower moving filler would be better for the first timer. In the end, I clamped down the largest gap during a rebraze and flowed some filler through it. Now it looks alright, althoug the lug is about two degrees off. Hopefully I can cold set it to place. My miter and fit pre-braze were good, so I have a feeling that the lift was caused by heat.

    I hadn't really thought about clean up, unterhausen. I was just hoping for a good first braze. But you're definitely right, the globs are going to be a pain. Unfortunately I don't have the resources to cut it up and try this one again right away, so I'm going to have to go on the hope that my flow was as good here as it was on my practice brazes. I guess I'll just have to hope for a soft landing if the connection snaps once this thing is done.

    Thanks again.

  5. #5
    Randomhead
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    you probably should try to close that gap and then fill it then

  6. #6
    tuz
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    2 degrees is a lot, I doubt you cold set it back that much? My joints sometimes are 1/2 a degree off the mitre, and it takes a bit of heat to move it back. It may be a sign things moved a bit too much. Can you spot an internal fillet in the joint? If your mitre was accurate, and the joint moved, there probably will be a gap in the mitre.
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  7. #7
    Randomhead
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    I guess I scanned his most recent post too quickly. You can't cold set that joint. If it's 2 degrees off, there is a pretty big problem and it really should be cut up. Sorry to have to say that. It would be worth the $30 in replacement parts to know what happened.

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