Does carbide flex ?
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    Default Does carbide flex ?

    I keep hearing during milling operations that "maybe the carbide is flexing ". As far as I know solid micro grain carbide doesn't flex. It is way too hard and brittle. I do high speed machining using very small tools .007,and even smaller. At the fees and speeds I am using if the took did "flex" it would probably be a matter of milliseconds before tool gave out.
    Any input is appreciated.

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    Quote Originally Posted by vrodsteve View Post
    I keep hearing during milling operations that "maybe the carbide is flexing ". As far as I know solid micro grain carbide doesn't flex. It is way too hard and brittle. I do high speed machining using very small tools .007,and even smaller. At the fees and speeds I am using if the took did "flex" it would probably be a matter of milliseconds before tool gave out.
    Any input is appreciated.
    .
    yes carbide obviously flexes. if just does not bend very far before it breaks. window glass flexes too but bend too much it breaks.
    .
    a dull tool will flex resisting cutting. rerunning often will cut more than expected cause under less load its bending less and cutting a little more.
    .
    after you machine 10,000 parts if you record data you might notice trends. if you record nothing a person often will miss what normally happens especially if subtle hard to notice things. you are cutting with micro tools. you have the chance to collect data on actual results

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    Yup, everything bends, no exceptions. How much before breakage, and how much force it takes to move it are the questions. With tiny carbide tools, they can bend a surprising amount before breaking, but go a little beyond their limit and it's goodbye.

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    size might matter a lot. fiber optic glass is tiny hair like and bends easily. obviously thick glass does not bend far before breaking

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    I drilled a few .010" holes using a carbide circuit board drill, viewing the operation under a microscope. Because the starting point was not well defined, the drill would sometimes wander on start. It was amazing to see how much that drill could flex. It would readily move over by as much as twice its own diameter and still drill a shallow hole successfully. I've also milled 1/16" wide slots using an .059 carbide endmill, and it would easily flex .003" because it would mill the slot to full width traversing the same toolpath in reverse direction with a spring pass.

    It's stiffer than HSS, but still not absolutely rigid. Mill a keyway full width with an endmill, it will always cut oversize if you cut both directions without any adjustment in Y.

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    I agree with everybody above, and add only this:

    Scale matters.

    For your 0.007" tool, a deflection of 50% of diameter before breaking would be a whopping 0.003'5". Which I don't think is visible to the naked eye. But when you measure your tiny feature on your close tolerance part with things like micrometers, that 3&1/2 thou will be obvious, and a problem.

    OK, so it won't bend 50%, it will bend 10% - 7 tenths. Which good instruments can measure.

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    I will try post a pic tomorrow, it does but not very well... It's why for difficult situations I'd prefer HSS because it can flex a bit more before failure. Im speaking about drills here, it is insane that I am going into a pre drawn hole in rebar that is so far off centre it's scary and a HSS drill only took 100 holes to snap off and break some safety glass... But the carbide is lasting pretty well... And I can near guarantee that it will snap a lot "easier" that the HSS just with a small noise because of the stress that is involved. The carbide is flexing, I can see it while it's drilling but someone blessed this drill to keep it going

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    Quote Originally Posted by DMF_TomB View Post
    a dull tool will flex resisting cutting. rerunning often will cut more than expected cause under less load its bending less and cutting a little more.
    Yeah definitely the carbide is doing all the flexing in that example. Couldn't be the toolholder, workpiece, workholding, or the machine itself since those are perfectly rigid.

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    Engineers use modulus of elasticity or Young's Modulus (abbreviated as E) as the measure of stiffness. The English unit is millions of psi and the metric unit is GPa. There are many different compositions for carbide tools because of the binder content, with different values of E. But for a rough comparison, tungsten carbide tools are about two to three times as stiff as carbon steel.

    Larry

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    [QUOTE=Milland;3176023]Yup, everything bends, no exceptions.

    Lies, nonsense!!

    Carbide is magic and does not obey the laws of physics. It has infinite Young's modulus and never ever flexes.

    Yep. True. I read it on the innernets.

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    Quote Originally Posted by jim rozen View Post
    Yup, everything bends, no exceptions.

    Lies, nonsense!!

    Carbide is magic and does not obey the laws of physics. It has infinite Young's modulus and never ever flexes.

    Yep. True. I read it on the innernets.
    Don't you argue with me! I know the heads of the FBI, CIA, KGB (or whatever they call themselves this year), Boris Badenov, and Vladimir Putin's cat, and they'll all come to your house and beat you up if you cross me!

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    Now, if you'll excuse me, I need to go hug my dakimakura of Taylor Swift until I calm down. I am super-triggered right now...

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    Micro grain carbide will flex/bend more than conventional before breaking, part of the reason it is so popular.
    High cobalt grades will take more at a tradeoff of hardness or life.

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    Quote Originally Posted by HuFlungDung View Post
    I drilled a few .010" holes using a carbide circuit board drill, viewing the operation under a microscope. Because the starting point was not well defined, the drill would sometimes wander on start. It was amazing to see how much that drill could flex. It would readily move over by as much as twice its own diameter and still drill a shallow hole successfully. I've also milled 1/16" wide slots using an .059 carbide endmill, and it would easily flex .003" because it would mill the slot to full width traversing the same toolpath in reverse direction with a spring pass.

    It's stiffer than HSS, but still not absolutely rigid. Mill a keyway full width with an endmill, it will always cut oversize if you cut both directions without any adjustment in Y.
    Same experience with small PCB carbide drills. 0.5mm carbide drill will flex suprising amounts. (just before it breaks)
    Typical 0.5mm PCB drill is maybbe 8mm to 12mm flute length so its pretty slender with 1:20 or so aspect ratio.


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