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  1. #1
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    Default Brazing Carbide Tips

    My current project is to make a 105mm core drill for use with soft sandstone. I have already made the core drill using some steel pipe. I cut material clearance slots in the business end then cut some grooves and slits for teeth. It cuts reasonably well but the steel sure does wear quickly. I lost around 5mm of steel for a 300mm core (and I have ALOT of coring to do).

    I have some rectangular carbide blanks that I would like to braze onto the core drill as the carbide should be more resistant than the steel. My plan is to braze them onto the end of the core drill in the material clearance slots. Think of the end of the core drill as being like an old castle wall top (casilated) with the inserts fitting into the gaps. The core drill is around 2mm thick and the carbide tips around 4mm thick, 12mm long and 6mm wide. I would like the carbide tips to overhang the core drill by 1mm inside diameter and outside diameter.

    My question is, if the carbide blanks fit reasonably tightly into the 'slot' in the core drill (I believe 3 to 5 thou " is required) will there be enough surface area to make a strong bond?

    I believe there is a technique called braze welding which does not rely on the capillary action but fills the edges/fillets more like a MIG/TIG weld. Would this be better?

    Also, what tip would be needed on teh oxy torch? A welding tip? Size?

  2. #2
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    Default

    Carbide tips are normally brazed with bronze brazing rod, or silver Solder/brazing rod, capillary action is a desired result, stronger bond, I would not attempt it
    with out Oxy/acetylene, tip size at a guess no. 7 You will then need to to flood the cut with water while drilling, otherwise the core drill will become too hot and the tips will part company with the body

  3. #3
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    Default

    just buy one, a lot less heartache

  4. #4
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    Default

    Hi Mk1_Oz, Guys,

    Yes a four inch (100 mm) core drill is a standard hole size. Here in the UK you can get one complete with a mandrel for less than £10. ($20 at the current exchange rate).
    100mm Core bit.jpg
    Best Regards:
    Baron J.

  5. #5
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    Default

    Quote Originally Posted by Mk1_Oz View Post

    My question is, if the carbide blanks fit reasonably tightly into the 'slot' in the core drill (I believe 3 to 5 thou " is required) will there be enough surface area to make a strong bond?
    Capillary action should get into the join OK. Be aware that the strongest braze joint has the smallest filler thickness - bronze braze gets weaker as the filler gets thicker. So less is better.

    Any brazing tip for oxy/acet or oxy/lpg should do it, but use a small flame pattern for more control.

    You may be able to go nickel bronze brazing rod (the strongest medium), but I've never used it and can't comment on it's suitability for carbide.

    Cheers Rob
    The worst that can happen is you will fail.
    But at least you tried.



  6. #6
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    I will be using oxy-acetylene (another learning adventure!). To buy a core drill bit is AUD$300 for a 120x450 diamond coveted bit with a 1 1/4 UNC thread. I have been told by several sources that the diamond bits are not good for soft materials as they will wear extremely fast. Counter intuitive but seems to be true.

    I will silver solder or bronze braze a get the joints nice and tight.

  7. #7
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    Quote Originally Posted by Mk1_Oz View Post
    I will be using oxy-acetylene (another learning adventure!). To buy a core drill bit is AUD$300 for a 120x450 diamond coveted bit with a 1 1/4 UNC thread. I have been told by several sources that the diamond bits are not good for soft materials as they will wear extremely fast. Counter intuitive but seems to be true.

    I will silver solder or bronze braze a get the joints nice and tight.
    As you are using oxy/acetylene there is no point in going silver solder. The high silver content rods you will need for the steel base are very expensive and the bond will be weaker than manganese bronze.

    So go to BOC and get some decent Profill uncoated rods and some Eziweld 303 dipping flux.

    That way you can apply just the amount of flux you want to prepare the join and be in control of the whole operation.

    Don't buy unbranded brazing rods from tool supply companies as they flow poorly, are usually coated, and are basically garbage in comparison to BOC offerings.

    Plumbing suppliers also generally sell good quality uncoated manganese brazing rods (possibly BOC) - if you want to buy them singularly.

    Cheers Rob
    The worst that can happen is you will fail.
    But at least you tried.



  8. #8
    Join Date
    Nov 2010
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    Frankston south
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    Quote Originally Posted by Mk1_Oz View Post
    I will be using oxy-acetylene (another learning adventure!). To buy a core drill bit is AUD$300 for a 120x450 diamond coveted bit with a 1 1/4 UNC thread. I have been told by several sources that the diamond bits are not good for soft materials as they will wear extremely fast. Counter intuitive but seems to be true.

    I will silver solder or bronze braze a get the joints nice and tight.
    Whilst what you have been told is partly true............Green concrete or softer materials require a harder bond to slow the wearing process. You are only coring Sandstone type material. $75 buys a 102mm core on ebay and they work ok, if you want you can spend $500 but I wouldn't, and I do this for a living

  9. #9
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    Quote Originally Posted by waxen View Post
    Whilst what you have been told is partly true............Green concrete or softer materials require a harder bond to slow the wearing process. You are only coring Sandstone type material. $75 buys a 102mm core on ebay and they work ok, if you want you can spend $500 but I wouldn't, and I do this for a living
    I just bought a $75 core drill bit and will see how it goes. Do you suggest a slowish speed and lots of water? Any other tips? I will be using a Husqvana DM230 core drill.

  10. #10
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    Quote Originally Posted by Mk1_Oz View Post
    I just bought a $75 core drill bit and will see how it goes. Do you suggest a slowish speed and lots of water? Any other tips? I will be using a Husqvana DM230 core drill.
    Slow speed, lots of feed and as little amount of water as you can get away with. only use as much water needed to get a slurry of wet toothpaste like consistency.

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