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  1. #21
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    How about a hollow CF structure filled with mercury?

    That will give you looks, weight, damping, and added thrill of having a couple hundred gallons of mercury on hand.

    Matt



  2. #22
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    One of the reasons for the popularity of cast iron is that it is self damping, so vibrations are rapidly removed by the material.

    The science behind "why this happens" is more complicated than this explanation, but basically it comes down to the fact that cast iron is not one, homogenous material, it is a mix of hard clumps and softer adhesive areas. The difference between these materials and how each behaves in relationship to the sound / vibration wave is what makes it damp out quickly.

    Epoxy granite mixes share this general concept, which is why they often damp very well.

    Al is completely different than cast iron in this way, which is why it rings like a bell. Some Al castings contain so much sand that they start to act a little like cast iron, but most Al material does not.

    Steel is somewhere in between, so it depends more on total mass to dampen, then dissipation inside the material. This is why you can fill a steel tube with sand, rubber, or other polymer coatings and it helps more than you might think.

    Ger21 tries to make the best of this mixed materials dampening effect by bonding Al and wood laminates together in his builds. He is more patient than most builders though and it appears that he spends at least 1/2 of this time building up layers. That isn't a criticism, just an observation that this approach is labor intensive.

    In theory, a composite fiberglass or carbon fiber could be made very stiff, and might actually be able to damp out vibrations very well. One interesting example is the new airbus 380. I have not flown it yet, but my friends that have claim it is MUCH quieter than the Al planes they are used to flying on. That is an indicator of good vibration dampening in a light structure. If you call a many ton vehicle a "light structure".

    There is a honeycomb polymer material used in high end boat building known for its vibration dampening. I don't remember the details though, but it is commonly sold down in the Florida area.



  3. #23
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    I made this beam as a support for solar panels on the boat i am building. It is 16mm endgrain balsa with 600 gram epoxy glass. The edges have been rebated and filled with 20 strands of 50K carbon tow. The round is only a couple of layers of glass over sone pvc tube and is only for decoration. When i made it i was surprised just how stiff it is and my thought at the time was it would make a good beam for a router. It s 2.6mtr long and only 90mm high. I tried to deflect it and twist it and it seems to be a lot better than a 100x50x4mm aluminium box section that i have but without putting a clock on it that is a bit subjective. I am only playing with a 6040 chinese machine at the moment and the boat takes priority but i will surely give it a try when i get to a bigger machine. Reading this thred i went and experimented a bit more and i am sure it would dampen a lot better than the ally section, i think the balsa, carbon and regular glass together would work a lot better than just solid carbon section.



    Mike



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    Default Since you're a millionaire....

    I say go for it. I am in the aircraft industry. Carbon fiber is a wonderful material. And since you'll do this when you're a millionair what do you have to lose but money? And for those pointing out vibration and resonance they have a point (the first all carbon fiber airplane has tuning forks all over to handle resonance issues). But who knows. Perhaps a composite lay up of alternaiting layers of carbon fiber, aramid, fiberglass, and, even aluminum. There is so much you can accomplish. You can design around resonance and vibration issues with an experienced composites engineer. A bit expensive but what the heck, you'll be a millionaire when you start this project

    Other ideas I would have for the best CNC ever... Mind reading capability would be nice. Definately pre tool crash shut down. Maybe there's a way to measure stresses inside of a cutting tool and send that feedback to the controller...auto feedback for speeds and feeds. Air bearings for linear travel. Some kind of ozone radiation based purifier for coolant systems. I HATE the smell of rotton coolant. I think a carbon fiber / composite gantry is quite possible with proper engineering.

    You wouldn't be fighting the inertial loads you would have with steel.

    Fun fun.

    Quote Originally Posted by flojor10 View Post
    So I was thinking if I ever became a millionare one thing I would do would be to build the best Cnc machine ever! So I started thinking about characteristics I wanted and of course speed, what my current machine lacks. So would a carbon fiber moving gantry be something to consider. I mean the material is amazingly stiff and lightweight. I also thought it might contribute to resonance, and weight could help, how much weight is desirable on the gantry to have a sturdy machine? And if anyone else has any ideas to make the best Cnc machine ever we'd love to hear them.




  5. #25
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    While there are many valid points in favor of CF, I still remain skeptical until a machine is made and provevn to work comparable to cast iron, steel or even aluminum. I'm not saying that a CF machine cannot work, just that I don't know if the the performance would be up to par, as well as the cost/benefit. The amount of labor cost alone would be tremendous, as molds need to be made, the CF has to be all laid and bagged by hand.

    The other thing is the vast majority of the products I've seen made with CF are parts that need to be strong, yet lightweight but still have some "give" or "flex" like autobody panels, boat and plane parts, etc. It would seem that to make something of CF so stiff that ot wouldn't flex would be to remove one of its major benefits...

    Yet another thing pointed out is that an ultralight gantry can be fixed to a heavy base. While I'm sure that this could work, the only real benefit would come from jobs that require an extreme amount of positioning. Today's higher-end CAM can reduce the amount of retracts and rapids significantly. A CF machine could only cut as fast as a comparable metal machine with the same spindle and components anyway, since the feedrates are ultimately limited by the drive system, spindle, and material being cut.

    While the point about the lightweight components having a lower "inertia," and therefore higher possible accelration, seems good, having parts that have more mass can be of benefit since they'll have a higher "inertia" and therefore more resistance to deflection.

    On another note, my last two machines were built of paper-based phenolics, which I suppose is created in a similar manner to CF as far as layering and resin bonding. I used 3/4" and 1" sheet, which does have some weight to it, and I suppose the phenolic combined with a "decoupling" of metal-to-metal parts helps with vibration damping. It is lighter than aluminum but heavier than wood (which was my first machine) and preobably heavier than CF of the same thickness (if there even is such a beast...)



  6. #26
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    CF laminates are only flexible when they are thin. Take a look at the chassis of a Formula 1 car. All carbon and over 1" thick in some places. It is NOT flexing there. You can make most anything using composites. It may be more expensive but it will work.

    Matt



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    the HSC / ultrasonic 20 from DMG has a carbon fibre gantry. the base is a variation of epoxy granite.
    DMG | DECKEL MAHO | GILDEMEISTER - HSC 20 linear | Precision Center

    its purpose of the carbon gantry is to reduce mass so that this machine can accelerate at over 2G.

    on high end mills, granite is the norm for bases, with everything else being iron or steel. carbon is rare, in fact i have only ever seen it on that DMG.

    on high end routers, its welded stress relieved steel frames. most likely to keep them affordable and easy to configure custom lengths.

    carbon IS used for metrology gantries. but its used for its low thermal expansion properties more than anything else.

    so, if i was picking the "best" setup for a mill, it would be granite and iron.
    for a router, probably granite and steel. i dont think id even consider carbon. just doesnt have properties that would put it above everything else overall.



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    Quote Originally Posted by keebler303 View Post
    CF laminates are only flexible when they are thin. Take a look at the chassis of a Formula 1 car. All carbon and over 1" thick in some places. It is NOT flexing there. You can make most anything using composites. It may be more expensive but it will work.

    Matt
    Yes I realize this; I work a lot with fiberglass and paper based phenolics and they are extremely stiff. My argument is that while one can use any material they want it doesn't necessarily mean it makes it a better machine regardless of price.

    Besides it would be so much easier and better to just buy the DMG machine if one had the money!



  9. #29
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    Quote Originally Posted by louieatienza View Post
    Besides it would be so much easier and better to just buy the DMG machine if one had the money!
    ha, i suppose that misses the point, but youd then be advocating a carbon gantry.

    that machine isnt super expensive, under 200k if i recall, but its only got an 8" cubed envelope.

    this is what you get for close to mil:


    epoxy granite base, an insanely over engineered asymetrical gantry that moves at 3900ipm and holds a 50hp 42000rpm spindle.

    if i was inclined to devote years of research and millions of dollars to "the best" machine, it would be like that one, but with more travel....



  10. #30
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    thats a beautiful machine



  11. #31
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    CF/epoxy tubing weighs 1.5 to 1.8 kgs/liter and steel 7.8. A CF/epoxy matrix is more that twice as stiff as steel.

    If you find a way to join cf tubes then you'd get a gantry twice as stiff and 1/4 the weight as a welded gantry.

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


  12. #32
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    Quote Originally Posted by compositepro View Post
    Carbon Gantrys are already in use

    I tried to drop this hint in the epoxy granite (theoretical as no one has made anything thread) its not rocket science its composites

    I actually do rocket science and composites. I'd only consider a CF machine for light duty like laser cutting or PCB milling. Too light for heavy milling, even though stiff, it will resonate badly. Just as rocket fins will resonate at a certain frequency for a given thickness/weight/speed, so will your machine. If that is accounted for in your design and proposed use, go for it. If you want the carbon fiber look, just use the vinyl decal stuff over your steel or wood and be done with it. Much easier than hand layups and vac bagging just to look cool.



  13. #33
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    It's not the material itself that's the issue, it's how it's used.
    Someone mentioned this earlier, but here's a direct link.
    Composite Machine Building Components

    Carbon fiber, will cost more, take longer, and require far more expertise, but you can very likely build a better machine with it.

    If you just want to build a gantry, build it like a torsion box. Mold the skins, and bond them to a torsion box framework. If resonance is an issue, make the skins thicker. You can use glass cloth to buildup thickness.

    If your trying to save weight, you're probably going about this all wrong, as in the end, adding weight will probably bring the most benefits.

    Gerry

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  14. #34
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    the dmg gantry is an i beam if i remember right (cant find any pics).

    they probabaly laminated it thick enough to be both stiff and have a resonant frequency away from the cutting frequencies (42000rpm / 20khz ultrasonic).

    this is a very light duty machine though.



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    Quote Originally Posted by ger21 View Post
    It's not the material itself that's the issue, it's how it's used.
    Someone mentioned this earlier, but here's a direct link.
    Composite Machine Building Components
    I checked out the link, pretty cool. They use filament winding. Anybody up for making an MDF based filament winding machine? I'd be interested in any links showing what's involved with DIY filament winders. Looks complicated.



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    Quote Originally Posted by Devastator View Post
    I checked out the link, pretty cool. They use filament winding. Anybody up for making an MDF based filament winding machine? I'd be interested in any links showing what's involved with DIY filament winders. Looks complicated.
    its not complicated at all. its basically a lathe of sorts, winding a spool of carbon tow thats passing through an epoxy bath.

    its really only good for convex tube shapes though. you could make a nice beam or core.



  17. #37
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    Quote Originally Posted by ihavenofish View Post
    its not complicated at all. its basically a lathe of sorts, winding a spool of carbon tow thats passing through an epoxy bath.

    its really only good for convex tube shapes though. you could make a nice beam or core.
    Sounds easy enough. From experience, some things look deceptively simple to me until I try to build them. I worry about a lot of unforseen variables in building a machine like that.



  18. #38
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    I checked out the link, pretty cool. They use filament winding.
    It looks like those wound holes actually are a bit more complicated than a lathe of sorts.

    Gerry

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  19. #39
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    Quote Originally Posted by ger21 View Post
    It looks like those wound holes actually are a bit more complicated than a lathe of sorts.
    im pretty sure those arent filament wound. by the looks, its just the outer and inner shells that are wound.



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    A few observations:

    Stiffness- The elastic properties of a material are only part of what contributes to stiffness, the other being how that material is arranged in space- its geometry. A small diameter rod and a large diameter hollow tube can have radically different stiffness with the same amount of material. But even talk of sectional shapes such as tubes or I-beams totally misses the opportunities of composites. Those sectional shapes are the natural result of particular materials and their manufacturing processes, which don't necessarily apply to composites. We can fabricate a much broader spectrum of forms, as well as vary the amount of material that is placed at any particular location. And design processes that utilize form-finding and topology optimization can result in geometric solutions that we couldn't possibly even begin to imagine, yet can be realized with composites.

    Anisotropic- Composites such as carbon fiber are highly directional in their strength, which instantly separates them from most of the other materials being discussed (at least for all practical purposes.) So not only can we explore the wider landscape of forms that are mentioned in the paragraph above, but within a given form we can control placement and direction of fibers, which has an impact on stiffness, ductility, damping, etc.

    Composite- In using “carbon fiber” and “composite” interchangeably we can lose sight of the fact that we are talking about a material that consists of a matrix that holds some other stuff within it. We can put other stuff in there beyond just carbon fibers. We can combine materials that have different engineering properties. Need more damping? Perhaps there is a way of combining a stiff material with one that has inherent damping capabilities. Perhaps we can determine that a material like that only needs to be incorporated in certain areas of the overall component. We are also ignoring that there is a good chance our gantry would be a sandwich construction with a core material. How this material contributes to the overall performance of the part needs to be considered.

    Overall, the three points above mean that we could create a composite gantry that is incredibly stiff, and possibly tuned to deal with resonance issues, while still being very light. And it would probably be some crazy shape that would look quite impressive. The knowledge and fabrication skills to design and fabricate it would be no small undertaking, but the possibilities are huge.

    Damping- I know little about resonant frequencies, especially as they pertain to machine design, so this one is a question: If stiffness can be kept exceptionally high, and therefore amplitude is exceptionally low, do we reach a point where frequency is a moot point?

    Goals- What exactly are the design goals here? “Best” at what? Asking the right questions at the very beginning of the design process would be crucial, otherwise we have no criteria to judge how successful this material might be. Especially since while designing anything we typically need to juggle multiple goals that conflict with each other.
    There isn't one person who doesn't like the look of cf, I need to incorporate cf in the build at least on the outside.
    If the primary goal is to look pretty, you can go with peel and stick vinyl that looks just like carbon fiber, and slash the budget considerably. :-)



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