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Would a pure diamond drill bit ever get dull?

  1. Jan 14, 2015 #1
    If a drill bit that was cut out of a single large diamond were made, would it last forever, assuming it was never used to drill through diamond and was never exposed to a laser? Would it ever get dull or break?
     
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  3. Jan 14, 2015 #2

    SteamKing

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    Without a doubt, it would be the most expensive drill bit ever made. Some drill bits are quite sizable.

    However, while diamond is hard, it is not indestructible. How do you think diamonds used in making jewelry are cut and faceted?
     
  4. Jan 14, 2015 #3
    Well, I imagine diamonds are usually fashioned with lasers. But I also realize that if you were to have a ten foot long drill bit made out of pure diamond, and you encased 5 feet of the bit in cement, and you applied enough torque to the other end, then you would snap the bit in half.

    But I'm wondering what would happen in normal conditions. What if you had a pure diamond drill bit, and did not abuse it. Would it cut holes in granite forever, without ever getting dull?
     
  5. Jan 14, 2015 #4

    SteamKing

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    Sorry, but that is incorrect. Lasers have only been around for a little over 50 years. Diamond cutting is quite a bit older and remarkably involves only the use of hand-held tools used by trained and highly skilled individuals.

    Ten feet is wildly larger than the largest diamond ever found.

    http://en.wikipedia.org/wiki/Cullinan_Diamond

    In its rough state, the Cullinan stone was a little over 10 cm (not 10 feet) in its largest dimension and had a mass of about 0.62 kg before it was cut into smaller stones.

    http://en.wikipedia.org/wiki/Diamond#Industrial-grade_diamonds

    Industrial grade diamonds are already used on some drill bits and as abrasives.

    http://en.wikipedia.org/wiki/Diamond_drilling

    AFAIK, these tools still need replacing periodically.
     
  6. Jan 14, 2015 #5

    Bystander

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    Diamond bits require coolant/lubricant to prevent heat buildup (C does burn in oxygen atmospheres), and to remove chips/waste.
     
  7. Jan 14, 2015 #6
    I know that a ten foot diamond is not realistic. I was just using that as an example to better understand physics. I also know that practically speaking, a bit made with diamond dust is most practical. I'm just trying to understand the physics a bit better. And so I'm asking hypothetical questions, rather than practical questions.

    So...

    Would a pure diamond drill bit, under ideal conditions, ever get dull from drilling through granite?
     
  8. Jan 14, 2015 #7
    Your question could be rephrased:
    Will the carbon atoms on the surface of a monocrystalline drill bit, continually being used to drill through granite, ever break their bonds with their neighboring carbon atoms?
    Yes:
    The carbon-carbon bond has a certain energy.
    The likelihod those atoms will remain in that bonded state can be estimated with the boltzmann distribution. http://en.wikipedia.org/wiki/Boltzmann_distribution
    Even if you continually cool the drill bit and have a liquid lubricant, statistically over long enough time, one of the carbon bonds will break.
     
  9. Jan 17, 2015 #8
     
  10. Jan 17, 2015 #9
    So now is that probability of a displaced molecule because of quantum mechanical fluctuations, or is it something else?
     
  11. Jan 17, 2015 #10

    Bystander

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    Heat from rubbing "this" against "that."
     
  12. Jan 17, 2015 #11
    as long as the diamond has an edge it will wear down the friction of drilling even into a softer material wont stop wear from occurring and without an edge it would do little actual drilling.

    take a butter knife only used for spreading butter onto toast even a stainless steel knife after years of use will show deterioration the steel is far harder than the butter or the cooked bread but they still have an cumulative effect on the steel. the same would be true on diamond.
     
  13. Jan 17, 2015 #12
    Yes, stresses due to cyclic loading will eventually cause the bit to break. The field that this encompasses is called "fracture mechanics". Similar tests are done with metals, computer chips, etc, where a stress or load is applied in a periodic matter until the part fails. Cant remember the exact name of the tests they do, but it is generally called "cycles to failure". Companies also use this concept to gauge how long warranties should last.
     
  14. Jan 18, 2015 #13
    the other issue with PURE diamond (I'm reading natural) is they are cut by exploiting the faults in the stone. natural diamond is riddled with faults which means many small diamonds usually result from larger finds. rarely do they find a large diamond with so few faults that a large clear diamond can be extracted. even the largest diamonds still have weak points left. making them susceptible to stress breaks (fortunately they are rarely subjected to very rough treatment like sharp impacts.) bits and blades are made of diamond dust added to the cutting surface like a carbide edge which acts like a hard to dull sand paper. the current industry is switching to hydraulic cutting because high pressure water cutting is far cheaper than blades for shaping stone. drills vary greatly depending on the stone expected to be drilled but many simply have exchangeable buttons and blades to reduce the total bit costs.
     
  15. Jan 19, 2015 #14

    Bandit127

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    Natural diamond gets dull from cutting plastic, let alone granite. 20,000 cuts to an optical finish across 15 mm diameter PMMA was enough to make the cut surface dull and put visible wear (under 200x magnification) on the edge.

    Diamond will also lose atoms to iron (to form iron carbides in a chemical reaction). "Wear" is dramatically increased in this scenario to the point that steel is virtually impossible to cut to an optical finish.

    Finally diamond also chips readily. I suspect this would be the predominant cause of wear in a drill that is cutting granite.
     
  16. Jan 20, 2015 #15
    I guess your basic question is if a cutting tool (not necessarily diamond) is harder than the material it cuts, will it last forever?

    All tools/tool tips are made harder that the material they are meant to cut, but eventually all of them wear out.
    Hardness is just resistence to wear, not absence of wear. Greater the hardness of a material, longer its life. But it isn't indestructible.
     
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