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Cone drill bit with threads to drill in hard rock formations?

  1. Aug 12, 2018 #1
    i designed a cone drill bit with right hand thread to give friction and grab inside to give pulling force. my question is can this type of cone drill bit drill hard rock formations like normal tricone drill bits with teeth or the cone drill bit will be weak to penetrate hard rock formations .

    Attached Files:

  2. jcsd
  3. Aug 12, 2018 #2
    One test is worth a thousand opinions......

    You can easily test your idea. Get a hardened steel screw, such as a drywall screw. Cut the head off, chuck it in a drill, and try it on a rock. Try soft rock first, such as limestone. You will quickly learn if the idea is valid.
  4. Aug 12, 2018 #3
    Three cone bits are rarely used these days, in comparison with two decades ago. Fixed cutter bits using Polycrystaline Diamond Compacts are the norm. Durability is a key issue and the PDC provides this. How do you envisage your design offering equivalent durability? What hydraulic design do you intend for cuttings removal?
  5. Aug 12, 2018 #4
    i didn't think it all through i was just seeing if the cone will perform like pdc if it is made of same material as pdc drill bits.
    i guess like you said its about durability so if it's made out of pdc then it will work. right?
  6. Aug 13, 2018 #5
    I would not give a categorical "no", but there are several issues and potential issues. I'm happy to work through some of these with you, if you wish.

    Now, you cannot make the cone of PDC. That is far to brittle and there is no practical way of adhering the diamond to the supporting bit body. The key word in PDC is Compact. The polycrystaline diamond layer is bonded to a tungsten carbide substrate by means of cobalt, which forms an interlinked phase between diamond and TC. These compacts, which range in size from 8mm - 19mm are then mounted in the body which is either steel or a tungsten carbide matrix material. Since you are targeting hard rocks, the latter would be the appropriate choice.

    Given all that, one major problem then lies at the point of your cone. This would be protected by a single PDC cutter. Moreover that cutter is presented parallel to the rock so that it drills by grinding, not shearing. One of the major benefits of PDC bits is that they drill by shear. Rocks are, generally, about half as strong when subjected to shear compared with compression. So, even if your point cutter provides adequate duability you have sacrificed rate of penetration. You might consider a chisel shaped cutter, as the technology is now up to producing simple shaped PDC. (The problem is exacerbated by the interbedded character of almost all drilled formations. This means that, at times, the point will be in hard rock and the other cutters in comparatively soft rock. The applied weight on bit will be alomost entirely on that lead cutter, with greatly increased risk of wholesale failure, or at least chipping.)

  7. Aug 13, 2018 #6
    i mean covering the whole cone and it's threads with polycrystaline diamond layer and the original cone and threads are out of TC. regarding the shear drilling,
    the cone drills by the thread grabbing onto formation with rotation and the point of the cone seperate the rock or you can say penetrate it and split it in half and then the whole cone grinds the remaining with every inch of the whole cone is in contact with formation on it's own at same time.

    the material and pdc i think is no issue as its doable but i would love if you could explain more about the shear drilling, my point is
    think of trying to drill in say butter with a tall cone like cylinder and with a fork.

    it's easier with with the cone like cylinder as penetration is easier and drilling continues as it moves with the threads. but with a fork the empty spaces between teeth like the pdc drill bits will leave remainings (cuttings).

    also keep in mind that the picture i attached is the cone inside the formation, the formation has same shape as cone so point of cone will sit on same area as the point's.
    every mm of the cone is facing the formation on it's own at same time.

    i'm trying to explain the picture i have in my head.

    let me know what you think.

    thank you
  8. Aug 18, 2018 #7


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    @ ahmed11.
    1. The grinding of every fragment into a fine powder requires much more energy than is needed to produce big fragments. Fine grinding is not only expensive and unnecessary, but it heats the bit and greatly reduce service life of the equipment. I suspect your cutter design grinds too finely to be economic.

    2. To remove rock fragments efficiently, remove one rock fragment at the time. Allow each fragment to fall into the hole vacated by the cutter or the previous fragment. Repeat that process. I cannot see how your design will allow the escape of big fragments.

    3. Avoid a flat face to face confrontation with solid rock. You cannot simply push rock out of the way with infinite force because there is an immovable mountain behind it. You must provide a high local pressure against it, then jump back. The mountain will respond by immediately pushing a fragment into the space vacated by the cutter pressure. By repeated loading the rock, unloading fractures form inside the rock, parallel with the local surface. Those fragments, once separated, can then fall out. How can your design produce the bit pressure variation usually generated by point percussion.

    4. In shallow holes compressed air may both drive and cool the cutters, then remove the spoil. In deeper holes water may be used. The deepest holes require a higher density fluid such as drilling mud that will flush and float the spoil from the hole. In your design I see no obvious path for the fluid flow in or out, needed to flush the hole.
  9. Aug 20, 2018 #8
    1. regarding the heat, the spiral thread on the cone drill bit grabs onto formation and rotates inside and every part of the cone gets in contact as same time even the threads so all of the cone with the threads will remain the same exact shape but smaller in size just like sharpening a pencil.

    2.Regarding the cuttings, the cone in contact with formation have minimal space between cone and formation so cuttings is generated from the void spaces between drill bit and formation, then the less the space the less the size for rock fragments.

    3. reagrding the face to face confrontation with the solid rocks i agree with you that it's difficult and requires more energy but imagine the cone with it's wide threads grabbing and cutting inside the rock as the point penetrates the rock the threads start to grab and cut inside the rock formations.
  10. Aug 20, 2018 #9


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    The “unicorn horn” type of drill works well for jobs like splitting wood. It is actually a rotating conical wedge that screws itself into the material until the material bursts away from the cone. That requires there be a vacant space close beyond the cutting face to receive the fragments, something rarely found underground. Caves in the formation are an expensive liability when rock drilling, not an advantage.

    The idea that the drill must pull itself into the formation involves a contradiction. The arctangent of the coefficient of friction between the wedge and the material, critically decides the angle of the cone or wedge used. Below the critical angle the wedge or cone will be self locking in the material, above that critical angle the cone will be spat out.
    If the wedge is too long and thin, it will wind into the material until it binds or locks. It will not be easy to pull backwards from the trap and it cannot be reversed because that would unscrew drill string couplings. A hidden problem with your design might be the single spiral cutter which effectively has a very gentle thread angle, much less than the cone, which will be significantly more prone to locking or seizing than will the bare conical surface.
    If the cone is sufficiently short and wide it will not pull itself into the rock. The bit force required to cut will be provided by the weight of the drill-string in the hole above, which is the way rock drilling usually works. A wide cone should not lock while gradually polishing the rock formation.

    Rock is more brittle than harder drill bits. Vibration or a high force applied to a low area of contact is needed to break and release rock fragments. That hammer drill vibration is not available with your drill bit. High pressure is not available since the cone area is all in contact at the one time.

    I expect the drill tip will probably break off the cone due to side forces on the bit as it cuts through a diagonal formation. There can in fact be no cutting point, because the fixed point theorem says the point will rotate but at zero abrasive velocity. You must have a hollow point that produces a cylindrical core, with some form of asymmetric core 'chip breaker' and a path for the chunks of broken core material to escape into the mud flow.

    Efficient cutting requires the generation of bigger fragments, not a rock powder that will form an active chemical cement. Your bit will generate a rock powder as it grinds or polishes, rather than cuts grit sized fragments from the rock formation.
  11. Aug 26, 2018 #10
    sorry for the late reply.

    what if we added pdc cutters on the threads and add on the rest of the cone itself friction surface like sand paper, will this give an advantage or no?

    by adding the pdc cutters on the threads we ensure that the threads with cutters will penetrate the rock formation and rotate inside them and the "sand paper like" on cone itself will grind the rocks efficiently.

    what do you think of this idea?

    i really appreciate you giving me the time and answering thoroughly with details.
  12. Aug 26, 2018 #11


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    I think you need to read Baluncore's reply carefully. He points out many issues that your design needs to address that existing designs have already solved.
  13. Aug 26, 2018 #12
    i know that existing drill bits are more efficient than the one i i'm talking about and as Baluncore pointed out the issues with my design but i just need to know if it can work or not.

    i just need to know will the cone design drill hard formations or not
  14. Aug 26, 2018 #13


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    If the cone angle is sharp, the drill will begin to break up when it pulls itself into the hole. If the angle is wide, it will slowly grind the rock to a powder. That will not be economically productive when compared to other available designs. So yes, while it might work, it would not be used as designed.

    It will not work as it is. I would suggest you test your designs outside an engineering workshop. Drill into a block of concrete or rock that can be replaced. That will reduce the cost of contaminating a valuable hole with hard materials as your experiments reveal problems. To see what went wrong you can split the block when your prototype gets jammed.

    Many small cutters are a liability because as they break off they take other cutters with them. Fishing for heavy non-magnetic cutter fragments in a hole will be very difficult because they do not float like rock fragments in drilling mud. Calyx drilling employs free abrasive in the hole, but it rapidly consumes the drilling tube wall, while producing a large diameter core.

    There will need to be modifications made as your design evolves by successive step changes into an optimised design. As with all optimisations that employ hill-climbing algorithms, you need to start at the bottom of the highest mountain, so you do not find yourself isolated on top of a sand dune. Unfortunately, I do not believe that your current design represents a good starting point that might reach the peaks occupied by other drilling technology today.

    You clearly need a challenge. Get to work welding hard facing materials onto earth moving equipment. Then start repairing used cutters from the rock drilling industry. Take short term jobs working on drilling survey or blasting projects. Read widely, and keep your ear to the ground. When there is an unusual problem, be the one that the operators call for advice on how others have overcome similar challenges.

    Before designing new solutions you must learn and know the game, so here is a challenge. How many ways are there to deviate a hole so as to drill around a broken drill bit jammed in the hole? Time allowed to answer that question, 40 years.
  15. Sep 5, 2018 #14


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    The cone shaped screw on the front of an auger drill bit works because it is able to compress the wood as it pulls the rest of the bit forward into the cut. This will not work on rock.

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