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Thread: Brazing 3/8 rod

  1. #1
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    Brazing 3/8 rod

    Hello, first post for me.
    I have 3/8 round mild steel rod that is coped to fit another 3/8 round mild steel rod. I want a tight and clean connection between the two with minimal post weld finishing. I tried both braze and silver soldering with mixed results. Area to be welded was cleaned with sand paper and acetone. Safety Silv Black was used as a flux.

    Silver solder - I think the flaw with my weld was I used a #0 heating tip, I believe I need a #5. Will need to try again with correct tip.

    Brazing seemed better as I switched to a #4 heating tip but only the backside (underneath heat direction) of the weld was connected.

    Does a successful weld come down to excellent heat control? What do I need to focus on? Any other suggestions for methods to achieve a tight connection like this?

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  2. #2
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    Re: Brazing 3/8 rod

    I think your rite #5 tip for 3/8" oa. I'm thinking you need something like Er70s for that tho. What is it? Do you have pics of the silver and bronze failures?

    With #5 tip you need 9 psi oxy 7 psi acety. I think you want a slightly carburized flame also, for me it's about the blue tip of the flame connecting with the work tho

    Disclaimer: I'm an amaeture

    What is it?

    Btw , nice copes

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  4. #3
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    Re: Brazing 3/8 rod

    Yeah heat control. Is the bottom photo brass filler. It you over heat if will not adhere.

    I watch the flux. With silver white paste, it goes from paste, then clear liquid, then dry white powder, then liquid again . the second liquid is when metal is near brazing temp. I do cheat and use the filler as an indicator of temp. I will drop a piece on the heat the near or the opposite side of the joint unit it flows

    Keep going, looks pretty good. Also, cut joints some to see how it flow.

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  6. #4
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    Re: Brazing 3/8 rod

    Quote Originally Posted by tapwelder View Post
    Yeah heat control. Is the bottom photo brass filler. It you over heat if will not adhere.

    I watch the flux. With silver white paste, it goes from paste, then clear liquid, then dry white powder, then liquid again . the second liquid is when metal is near brazing temp. I do cheat and use the filler as an indicator of temp. I will drop a piece on the heat the near or the opposite side of the joint unit it flows

    Keep going, looks pretty good. Also, cut joints some to see how it flow.

    That's a good explanation of how to read the flux transition. Thousand thankyous. I would break the flux off of 7018 or 6010 to use for tig filler but the op had a good oxyacetylene question.


    Edit
    Or use Er70.
    Last edited by Insaneride; 07-10-2020 at 11:36 PM. Reason: Er70

  7. #5
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    Re: Brazing 3/8 rod


    Stinker79


    Quote Originally Posted by Stinker79 View Post
    . . . I want a tight and clean connection between the two
    with minimal post weld finishing . . .
    I am fluent - with most of your 'process attempts'. You failed
    to mention - is this a structural, or cosmetic joint - I have
    multiple answers . . .


    hth


    Opus





    .
    Last edited by OPUS FERRO; 07-11-2020 at 12:56 AM. Reason: . . . too much - might be too much . . .

  8. #6
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    Re: Brazing 3/8 rod

    Wow thanks for the quick and helpful feedback!

    Answering your questions:

    This is for a wall mounted cross, a purely cosmetic part. 12in x 6in or so in dimension. I will end up gold plating it, or various other finishing techniques.

    For the brazing technique I am using Harris brand 1/16 un-coated LFB (low Fuming Bronze). I just had it laying around. I can pick up some ER70S, and am open to other flux options. Im happy to spend a few bucks to get the process and materials correct.

    I also have a TIG welder and had a buddy tell me to try fusion welding the joint, but I am afraid of losing the tip of the cope with that process.

    Thanks again for the help!

  9. #7
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    Re: Brazing 3/8 rod

    3/8" is a little thick for brazing but could still work. You won't be able to braze it without building it up though. Each piece needs to be heated close to red hot without melting and then the brazing rod added. It's not like soldering copper pipe where capillary action pulls the filler metal in. If mounting on a wall I'd just weld it from the back side with Tig. If you're good with Tig you could put put a nice small bead all around it. Tig won't work with the brass on the rod though.

  10. #8
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    Re: Brazing 3/8 rod

    Quote Originally Posted by Welder Dave View Post
    3/8" is a little thick for brazing but could still work. You won't be able to braze it without building it up though. Each piece needs to be heated close to red hot without melting and then the brazing rod added. It's not like soldering copper pipe where capillary action pulls the filler metal in. If mounting on a wall I'd just weld it from the back side with Tig. If you're good with Tig you could put put a nice small bead all around it. Tig won't work with the brass on the rod though.

    Thanks, the capillary action is why I tried silver solder (Safety Silv 56), which I found should have more of a capillary quality to it.

    Ill update some trials when I get back in the shop this weekend

  11. #9
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    Re: Brazing 3/8 rod

    Might be hard to get equal heat on the 2 pieces for silver solder.

  12. #10
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    Re: Brazing 3/8 rod

    Quote Originally Posted by tapwelder View Post
    Yeah heat control. Is the bottom photo brass filler. It you over heat if will not adhere.

    I watch the flux. With silver white paste, it goes from paste, then clear liquid, then dry white powder, then liquid again . the second liquid is when metal is near brazing temp. I do cheat and use the filler as an indicator of temp. I will drop a piece on the heat the near or the opposite side of the joint unit it flows

    Keep going, looks pretty good. Also, cut joints some to see how it flow.
    This is an excellent explanation and I agree totally!
    Silver solder is my favorite method for joining small parts, especially brass and stainless steel.
    I can't recall if I have ever used it to join mild steel though.

    Heat control absolutely!
    Your picture of your attempt at silver solder looks like it was overheated.
    The line between not enough heat and too much is very small and is why most people get frustrated!
    Silver also likes for the temp to be the same throughout the joint. With your small parts this should be much easier!
    Keep the torch moving in a small circle so that it heats all the parts evenly.
    If you are not naturally patient then you will have a much harder time with silver solder.
    Once I "find the proper temp" for the silver to flow I use what I call a fly fishing motion to maintain the proper temp.

    The only other suggestion I have is like TIG silver solder needs the parts to be very clean!

    I believe you are on the right track.
    Practice on some scrap first though!
    The first time "it happens" is amazing and happens so quickly you can almost miss it!

  13. #11
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    Re: Brazing 3/8 rod

    Try tig brazing.











    Sent from my iPhone using Tapatalk

  14. #12
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    Re: Brazing 3/8 rod

    OK attempt #2

    Used a #4 heating tip, its the biggest I have right now.

    Bronze joint likely got too hot. Its connected but the fill is not closing the gap on the cope connection. Will attempt again I know I am better than this.
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    Silver joint looks perfect ... on one side. The problem is that the cope was misaligned in my jig and the other side has a big gap. I watched the flux carefully and had a good feel for heat control this connection. I will improve the stability of my welding jig and I have hope that this could be my solution.
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    And this was attempt with fusion TIG. The tip of the cope got blown out as I expected, and there is undercut. Right now this is not my preferred method. It looks black because I treated it with
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    I will give TIG brazing a try as well. First I'll try the Silver solder, and order some silicone bronze 1/16 rod.


    Im no stranger to Silver Solder. I used it for joining 1/4in half round rod in a mild production setting. Probably made close to 300 of these joints with a very high yield rate.
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    Thanks again for all the suggestions!

  15. #13
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    Re: Brazing 3/8 rod

    For silver brazing the joint needs to be very tight, 56% is very fluid, 45% may be better.

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    Richard

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  17. #14
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    Re: Brazing 3/8 rod

    I was able to solve my problem! I started by re-designing my fixture to assure parts always lined up exactly the same way each time - I used a laser cut piece that the rounds seated into. I also had a local machinist cope a bunch more rods for me to assure they are dead nuts accurate. With the tight fit up and some Safety Silv 45 it is super easy to make the clean connection I wanted. Thank you for all your input! I learned a lot and was able to apply the knowledge gained.

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  19. #15
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    Re: Brazing 3/8 rod

    Nice. Can you share photos of the fixture?

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    Re: Brazing 3/8 rod

    If you’re going to plate that afterward I would suggest starting by cleaning up the surface of the round bar in a lathe befor you weld it. That will drastically reduce your prep time for planting and provide a more consistent result.
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  21. #17
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    Re: Brazing 3/8 rod

    Quote Originally Posted by scsmith42 View Post
    If you’re going to plate that afterward I would suggest starting by cleaning up the surface of the round bar in a lathe befor you weld it. That will drastically reduce your prep time for planting and provide a more consistent result.
    I dont have a lathe, although I did remove mill scale with emery cloth on the non coped rod beforehand. I will be plating them but they will be blasted first for a matte texture so that should reduce the appearance of imperfections

    Thanks

  22. #18
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    Re: Brazing 3/8 rod

    Depending on what look you are after. A file would allow a close finish for removing excess filler.

  23. #19
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    Re: Brazing 3/8 rod

    Quote Originally Posted by Stinker79 View Post
    I was able to solve my problem! I started by re-designing my fixture to assure parts always lined up exactly the same way each time - I used a laser cut piece that the rounds seated into. I also had a local machinist cope a bunch more rods for me to assure they are dead nuts accurate. With the tight fit up and some Safety Silv 45 it is super easy to make the clean connection I wanted. Thank you for all your input! I learned a lot and was able to apply the knowledge gained.

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    That looks really good.

    My problem, because I don't do much brazing that involves capillary action is.....................I NEVER KNOW WHEN THE JOINT IS FILLED I keep melting that rod into the joint. I literally don't know when I should quit

    Judging by what you say, you probably don't own a milling machine. The process to cope that small stuff is really quite simple.......just a plunge cut with an end mill. Anyways...........take care....looks good

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