Brazing thick steel -advice please.
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  1. #1
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    Brazing thick steel -advice please.

    I've done a fair bit of braze welding of cast iron etc before, but have never had to braze capiliary type) anything other than sheet steel which always went OK.

    I have a large headed bolt to which I want to braze (with a fluid tight seal) a piece of rod about 1/2" thick. I tried a practice pair of pieces - also with machined finishes - but could not get the brass to flow between them with that capiliary action. It ended up simply brazing them together with a bead around the perimeter, when I sectioned the pair there was no braze between them.
    Figuring the machined finish is the problem (no gap to speak of) I wonder if I temporarily put a 2 thou shim between them and put a Mig tack on one side to maintain a gap, remove the shim then try to braze them together? Seems like the kind of fuss that a real welder would not go through so I am looking for advice.

    The ultimate aim is to drill through the whole assembly, then redrill to a larger diameter and tap the 1/2' slug and affix a drain tap for my parts washer. Not enough meat in the bolt itself.

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  2. #2
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    Re: Brazing thick steel -advice please.

    did u use any flux?

  3. #3
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    Re: Brazing thick steel -advice please.

    Flux coated rods.
    I also sprinkled some Petersons #1 around the periphery of the joint, but not between the pieces. If I had a liquid flux I might have painted it on between the pieces but all the liquid fluxes seem to be for silver brazing or soldering.

  4. #4
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    Re: Brazing thick steel -advice please.

    I think the flux is water soluble, if not you can still preheat the pieces and flux them, set them & braze. I think you will find it necessary to have flux between the pieces to do what ya wanna do.
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  5. #5
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    Re: Brazing thick steel -advice please.

    "Tin" the parts with a light coat of bronze, then assemble and heat to stick them together.

  6. #6
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    Re: Brazing thick steel -advice please.

    Just to add to what has been stated. You could also, bevel the cylinder. This would expose more surface area and assure clearance for flow. If you have a lathe then you can machine the necessary clearance. A button machined on the bottom would allow you to hold the part with pressure as there is a possibility of the part floating/shifting when the flux goes liquid.

  7. #7
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    Re: Brazing thick steel -advice please.

    Use something with more silver. It wicks better.

    I’d use a liquid or thin film of paste flux, and a piece of foil thin brazing alloy placed between the cold parts.

  8. #8
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    Re: Brazing thick steel -advice please.

    I've brazed machine screw heads to steel plates but nothing larger than 1/4tr". Filler flow's to heat,I'm thinking it might be difficult getting center hotter than perimeter. Just thinking aloud. How about running a test where flux is applied to surfaces, bare bronze filler hammered flat,placed between parts and heat until filler appear's around edge. I would heat both parts far away from center until they are hot enough or at least near melting filler before moving flame nearer joint. I would try completing job without ever putting heat directly on joint. I don't recall a procedure for brazing this type joint so it very well might not be possible doing a first class job. I figure you've considered beveling,welding and machining.

  9. #9
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    Re: Brazing thick steel -advice please.

    How big is the bolt?

    Are you getting things hot enough?

    Why not just MIG it?

  10. #10
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    Re: Brazing thick steel -advice please.

    Drill undersized, braze, drill to full size.
    My name's not Jim....

  11. #11
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    Re: Brazing thick steel -advice please.

    Twas me, and I do stuff weird I guess

    You need clearance for the bronze to flow between the parts.

    Kiss the backside of your turned round stock with a slightly smaller mill, then put a few slots around the unmilled perimeter so's you can melt the rod into the inside of the cavity you made. Can do the same sorta thing with a lathe.

    This method allows you to place the parts in proper orientation while clamped, and the unmachined perimeter will hold your gap, and dimensions. Then you got an almost 80-90% fully brazed/sealed area to drill through.

  12. #12
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    Re: Brazing thick steel -advice please.

    Gonna need a lot of heat...……..rosebud comes to mind. Keep the heat on the round stock mostly, and let it wick into the bolt head. Then you have less chance of overheating the bolt and messing up the wrench lands. MIG that bastd, and you're gonna mess up the hex lands (or whatever they're called). I found the real beauty of brazing is the fact it's non destructive. Great stuff.

  13. #13
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    Re: Brazing thick steel -advice please.

    Alternatively

    Turn a shoulder on the backside, leaving enough meat to drill thru, and braze it up around the shoulder. Gap is a gap, and the meat ya leave is enough to hold the parts in orientation when clamped.

    Hell...….a bronze filler can reach 65ksi tensile...strong stuff really. Long as you got some good amount of area for contact, you gotta winner

  14. #14
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    Re: Brazing thick steel -advice please.

    Quote Originally Posted by 12V71 View Post
    "Tin" the parts with a light coat of bronze, then assemble and heat to stick them together.
    +1

    Quote Originally Posted by Wild Turkey View Post
    Are you getting things hot enough?
    +2

  15. #15
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    Re: Brazing thick steel -advice please.

    according to this just resting the mill quality parts on each on each will give sufficient clearance for brazing. Polished parts would require added joint clearance. Perhaps drill your holes first then you can see if it is flowing,also reducing mass.

    https://www.thefabricator.com/articl...essful-brazing

  16. #16
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    Re: Brazing thick steel -advice please.

    Put 2-3 centerpunches in the joint to give 3-5 thou clearance. Preheat the whole thing to black heat (800-900F).
    Then braze. You won't need a huge torch with everything preheated.

    Pretinning is a great idea too.

    metalmagpie

  17. #17
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    Re: Brazing thick steel -advice please.

    Quote Originally Posted by farmersammm View Post
    Gonna need a lot of heat...……..rosebud comes to mind. Keep the heat on the round stock mostly, and let it wick into the bolt head. Then you have less chance of overheating the bolt and messing up the wrench lands. MIG that bastd, and you're gonna mess up the hex lands (or whatever they're called). I found the real beauty of brazing is the fact it's non destructive. Great stuff.
    Agreed. V MFA6 then I put a #5 tip and pick up the fluxed rod( generally Harris)

  18. #18
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    Re: Brazing thick steel -advice please.

    Lots of GREAT thoughts and idea. Thanks very much guys. I think I know how I am going to proceed now.

  19. #19
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    Re: Brazing thick steel -advice please.

    Quote Originally Posted by 12V71 View Post
    "Tin" the parts with a light coat of bronze, then assemble and heat to stick them together.
    My advice also.
    A slight gap between pieces gives a place for the bronze to flow into.
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  20. #20
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    Re: Brazing thick steel -advice please.

    Go to summit , dorman 65241 transmission drain plug . Already built for you ! 4.99 ! It will be delivered the next day !

  21. #21
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    Re: Brazing thick steel -advice please.

    Quote Originally Posted by paul. m View Post
    Go to summit , dorman 65241 transmission drain plug . Already built for you ! 4.99 ! It will be delivered the next day !
    I was thinking the same. The local parts stores around here carry them for the guys that push snow. They run temp gauges on the trans and change fluid when they over temp a trans. Saves rebuilding the trans a couple times a season.

    As for the original question about brazing? The prefluxed rod is probably LFB15 which is for braze welding where building a bead is desirable. LFB is for sweating joints and wets out better than LFB15. I personally dislike the prefluxed rod as it has way too much flux, and makes clean up more difficult. Brazing flux can be mixed with water and used as a paste. I use distilled water and mix it to the consistency of thin tooth paste. Apply it with an “acid brush”. I keep it in a small plastic pot with an airtight lid (available at the Dollar Store).

    OK back to the filler material. There needs to be a gap of .001” to about .010” for the filler to flow or “wet” the flying surfaces. To avoid costly fit up time a manufacturer would probably use a preformed filler disc and just flux the flying surfaces, stack the parts, and oven braze the assembly.

    Back when I dabbled in jewelry making, I could get silver solder powder in varying alloys of silver content. We used it to attach wire to sheet as when doing glass enameling work. You would clean the surfaces and spread the solder powder on a sheet of paper, then paint the flying surface of the application with a sizing and pick up the solder which would adhere to the sizing. Align the parts and solder with a torch.

    Back to the original question, Yes you can braze that piece. Is it worth the time and effort? NO! Spend the $4.99 and save yourself a bunch of head aches. As the infamous Racin Jason used to admonish me “Life is too short to struggle needlessly.”
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  22. #22
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    Re: Brazing thick steel -advice please.

    Well, i don't think I could find a drain valve that would fit, it didn't seem to be metric, SAE of pipe thread!

    The story is a youtube video gave a parts list of the various bits needed to upgrade some features of the Horror Fright Parts washer. I bought them, the vid stated that the drain valve was a 14mm. I never thought to check my parts washer - it's been sitting in my shed for at least twenty years and turns out it was made in Taiwan rather than the current Chicom one. The Taiwanese used a different sized drain plug - about 16.5mm or so - so the new $17 14mm drain valve is way too small. Rather than waste the money for the valve and have another useless thing knocking around in a drawer somewhere I thought I would go the route I mentioned.

    I apologize for the following pictures being too big and sideways!

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    Also, as a weekend warrior, it's not a waste of time to me. From this thread and the dicking around I have learned quite a bit.

    So using the wisdom from this thread, I first used a smaller diameter piece of bar stock and dfrilled it out to a 1/4" then part drilled it out to the 1/2" required for the 14mm thread. I drilled out the drain plug to 1/4" and used a short length of 1/4" rod to register them. On the mating side of the rod I turned it leaving a small ring a couple thou deep for the "gap". I then tinned both sides, assembled them and went to town with the brazing rod.

    The eff up that isn't obvious from the above is that the piece of scrap rod I picked out of one of my buckets was drill rod, and the heating and quench cycles turned it into diamond!!

    My 1/2" drill bit was unable to finish the drilling out to a half way through the bolt head which was the plan. The drill bit could no longer cut the rod. Luckily, I have a 1/2" solid carbide end mill which I chucked up in th lathe and it cut the hardened tool steel like butter.

    Of course, cutting the thread was another story..............I don't have a carbide 14mm tap! It was super slow going and the tap was just able to thread the hardened steel enough for full engagement of the drain valve. Another lesson learned!

    The assembly doesn't leak and I'm happy with it. TBH I can't tell if the brass wicked between the parts or not because it wicked up the sides and formed an outside seal anyway.

    So there are brazing rods and braze welding rods? I bought these when I braze welded up the cast iron leg assembly on my stomp shear. I never knew there were two types?

  23. #23
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    Re: Brazing thick steel -advice please.

    That turned out nicely

  24. #24
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    Re: Brazing thick steel -advice please.

    Nice job!

    You probably should have taken the red hot part, and dropped it into a pile of wood ash, then raked some over it to let it cool more slowly. That would have left it annealed (after an hour or so).

    I wouldn’t say there are braze welding rods. But some brazing rods are meant to flow out, and some are meant to build a fillet.

  25. #25
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    Re: Brazing thick steel -advice please.

    Quote Originally Posted by rlitman View Post
    Nice job!

    You probably should have taken the red hot part, and dropped it into a pile of wood ash, then raked some over it to let it cool more slowly. That would have left it annealed (after an hour or so).

    I wouldn’t say there are braze welding rods. But some brazing rods are meant to flow out, and some are meant to build a fillet.
    Yep, I would've done if i had known it was tool steel. That's the trouble with a scraps bucket!

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