Epoxy granite but graphite?


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Thread: Epoxy granite but graphite?

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    yoobsterlol's Avatar
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    Default Epoxy granite but graphite?

    I've been trying to design a diy cnc machine that is able to mill steel. After a long time of looking at other designs, both from commercial and diy machines, I've seen a lot of good things about epoxy granite. Then I started thinking about the use of graphite powder instead granite pieces and wondered whether they would come out with similar or even superior qualities. The reason I say this, is because carbon fibre is made in a very similar way, well....using carbon fibres. Carbon fibre being a very rigid material, I figured it would serve as a good replacement. There's probably a million reasons why this is a stupid idea, but I haven't come across any builds that confirm this so I figured I would bring it to the smart people. Is there any specific reason that substituing graphite powder in for granite might be a bad idea? (Also don't hate pls I'm a 16 year old highschool student with absolutely zero education in physics, at least for now, as I am considering going into mechanical engineering.)



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    Default Re: Epoxy granite but graphite?

    Welcome and great to see enthusiasm!

    Perfect opportunity to research the physical properties of granite and carbon based composite materials. You'll need to find out about density, vibration, rigidity and the ways these physical properties apply to the mechanical aspects of mechanical motion based machines. Look at the forces applied in 3 dimensions (or more) and how to addresses those. How to move mass around (and stop it).

    Other experienced builder folks here can chime in and provide some feedback.

    Great project with a practical goal/application in mind.

    Good luck!



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    Default Re: Epoxy granite but graphite?

    I don't think that graphite powder plus epoxy will be any stronger than epoxy and any other kind of powder. The physical structure of the granite, optimally graded from coarse to fine with a minimum of glue holding it together, is what gives epoxy-granite its strength. Carbon fiber is different from graphite powder - due to its linear structure, it does add tensile strength to materials it's mixed with. But don't take my word for it - mix up some test batches of graphite and epoxy and granite and epoxy, cast them into bar shapes, and then try breaking them with compressive forces. See which one breaks easier.

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Quote Originally Posted by awerby View Post
    I don't think that graphite powder plus epoxy will be any stronger than epoxy and any other kind of powder. The physical structure of the granite, optimally graded from coarse to fine with a minimum of glue holding it together, is what gives epoxy-granite its strength. Carbon fiber is different from graphite powder - due to its linear structure, it does add tensile strength to materials it's mixed with. But don't take my word for it - mix up some test batches of graphite and epoxy and granite and epoxy, cast them into bar shapes, and then try breaking them with compressive forces. See which one breaks easier.
    See, I can totally understand the reason why carbon fibre has the properties is does(very similar to wood grain structure for example), but the exception I'm seeing with graphite and carbon powder in general, is that it is already used to make very stiff objects, in the form of carbide tooling, with this epoxy graphite mixture using epoxy as the matrix as opposed to cobalt or something like that. While of course I can't expect something held together by epoxy to come close to carbide tooling, I still feel like there must be something there to go off of. I will take your suggestion of making some test pieces, who knows, maybe I just created a super material ??



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    Default Re: Epoxy granite but graphite?

    Yes, carbon is a component of tungsten carbide (and diamonds), but that doesn't mean that adding carbon to things always makes them harder. Making some test bars and destroying them will give you more visceral insight into all this than any amount of explanation online.

    [FONT=Verdana]Andrew Werby[/FONT]
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    Quote Originally Posted by awerby View Post
    Yes, carbon is a component of tungsten carbide (and diamonds), but that doesn't mean that adding carbon to things always makes them harder. Making some test bars and destroying them will give you more visceral insight into all this than any amount of explanation online.
    I'll definetely try to do some tests and see what happens. My understanding with the use of granite is that larger pieces have less surface area than if the same area were to be filled with powder, aiding in having the lowest amount of epoxy as possible, and of course a large piece of graphite would be quite brittle so that wouldn't work so well. I hope I don't come across sort of a know-it-all, I'm just trying to absorb as much knowledge from people as possible, and find out if any information I have already is accurate.



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    Default Re: Epoxy granite but graphite?

    Hi,
    graphite is carbon in the sp2 hybridized state. In that state it bonds to three other carbon atoms forming sheets. The only forces between sheets
    holding the graphite solid together are Van der Walls forces. Consequently graphite is weak and brittle.

    Diamond on the other hand is carbon in sp3 hybridized state and bonds with FOUR other carbon atoms in a 3D lattice and is strong.

    Carbon fiber is graphite but is aligned 'in the plane' of graphite or if you like a 'sheet cut into long narrow strips'. While graphite might
    be weak between adjacent sheets a strip pulled lengthwise is strong.

    When a carbon fiber composite is made the strength of the product is high in the direction that the graphite strips or ribbons are laid
    but weak in other directions. To make a strong product requires carbon fibers must be laid in all directions.

    One of the great challenges of making fiber reinforced products is to minimize the resin relative to the fiber, the fiber being strong but
    the resin not. A hand lay up is unlikely to achieve a fiber to resin ratio of better than 3:1. Even achieving that becomes harder and harder
    as the number of different fiber directions increases. So much so that if you chop the fibers into short lengths and mix it with resin the ratio
    of fiber to resin is likely to be 1:2, that is more resin than fiber, sometimes called 'fiber filled plastic'.

    Were you to attempt to make a machine that way the cost of the resin would soar. I realize you are proposing to use graphite rather than
    carbon fiber but the probability of you achieving a castable mixture of less than 30%-50% resin is slim. Even that would count against
    the economics of the technique.

    Where granite-epoxy comes into it own is a graded series of sizes granite down to granite sand. Then resin to granite ratios of 1:10
    have been reported.

    If you could take solid graphite and crush it into a graded mix of little chunks right down to sand sized grains you might achieve a reasonable result.
    But then how does that differ from making a graded mix of granite?

    Craig



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    Quote Originally Posted by joeavaerage View Post
    Hi,
    graphite is carbon in the sp2 hybridized state. In that state it bonds to three other carbon atoms forming sheets. The only forces between sheets
    holding the graphite solid together are Van der Walls forces. Consequently graphite is weak and brittle.

    Diamond on the other hand is carbon in sp3 hybridized state and bonds with FOUR other carbon atoms in a 3D lattice and is strong.

    Carbon fiber is graphite but is aligned 'in the plane' of graphite or if you like a 'sheet cut into long narrow strips'. While graphite might
    be weak between adjacent sheets a strip pulled lengthwise is strong.

    When a carbon fiber composite is made the strength of the product is high in the direction that the graphite strips or ribbons are laid
    but weak in other directions. To make a strong product requires carbon fibers must be laid in all directions.

    One of the great challenges of making fiber reinforced products is to minimize the resin relative to the fiber, the fiber being strong but
    the resin not. A hand lay up is unlikely to achieve a fiber to resin ratio of better than 3:1. Even achieving that becomes harder and harder
    as the number of different fiber directions increases. So much so that if you chop the fibers into short lengths and mix it with resin the ratio
    of fiber to resin is likely to be 1:2, that is more resin than fiber, sometimes called 'fiber filled plastic'.

    Were you to attempt to make a machine that way the cost of the resin would soar. I realize you are proposing to use graphite rather than
    carbon fiber but the probability of you achieving a castable mixture of less than 30%-50% resin is slim. Even that would count against
    the economics of the technique.

    Where granite-epoxy comes into it own is a graded series of sizes granite down to granite sand. Then resin to granite ratios of 1:10
    have been reported.

    If you could take solid graphite and crush it into a graded mix of little chunks right down to sand sized grains you might achieve a reasonable result.
    But then how does that differ from making a graded mix of granite?

    Craig
    This is actually some really good information, thank you. I wasn't particularly set on the use of graphite or anything, mostly asked to find if anybody has done anything with it before, and it's apparent that there are some serious issues that would be present with the use of graphite. I think it would probably be best to use graded aggregate considering the information I have been given. Me being a hobby luthier has taught me the importance of having as little adhesive between the pieces as possible, and it seems that it's the same for epoxy granite. I really do appreciate the information, there's more in this one reply than what I've been able to find on my own for the past 2 weeks(although I've spent more time modeling my machine rather than researching frame materials).



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    Community Moderator ger21's Avatar
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    Default Re: Epoxy granite but graphite?

    The strength in carbon fiber comes from the fibers. Graphite powder has no fibers, and hence, no strength at all.

    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by joeavaerage View Post
    Hi,
    graphite is carbon in the sp2 hybridized state. In that state it bonds to three other carbon atoms forming sheets. The only forces between sheets
    holding the graphite solid together are Van der Walls forces. Consequently graphite is weak and brittle.

    Diamond on the other hand is carbon in sp3 hybridized state and bonds with FOUR other carbon atoms in a 3D lattice and is strong.

    Carbon fiber is graphite but is aligned 'in the plane' of graphite or if you like a 'sheet cut into long narrow strips'. While graphite might
    be weak between adjacent sheets a strip pulled lengthwise is strong.

    When a carbon fiber composite is made the strength of the product is high in the direction that the graphite strips or ribbons are laid
    but weak in other directions. To make a strong product requires carbon fibers must be laid in all directions.

    One of the great challenges of making fiber reinforced products is to minimize the resin relative to the fiber, the fiber being strong but
    the resin not. A hand lay up is unlikely to achieve a fiber to resin ratio of better than 3:1. Even achieving that becomes harder and harder
    as the number of different fiber directions increases. So much so that if you chop the fibers into short lengths and mix it with resin the ratio
    of fiber to resin is likely to be 1:2, that is more resin than fiber, sometimes called 'fiber filled plastic'.

    Were you to attempt to make a machine that way the cost of the resin would soar. I realize you are proposing to use graphite rather than
    carbon fiber but the probability of you achieving a castable mixture of less than 30%-50% resin is slim. Even that would count against
    the economics of the technique.

    Where granite-epoxy comes into it own is a graded series of sizes granite down to granite sand. Then resin to granite ratios of 1:10
    have been reported.

    If you could take solid graphite and crush it into a graded mix of little chunks right down to sand sized grains you might achieve a reasonable result.
    But then how does that differ from making a graded mix of granite?

    Craig
    You have explained well Craig. Just learn lots of things from your post.



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Epoxy granite but graphite?