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  1. #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...)



  2. #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.

    wotzBotz


  4. #28
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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!



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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....

    wotzBotz


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    thats a beautiful machine



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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


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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.



  9. #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

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

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


  10. #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.

    wotzBotz


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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.

    wotzBotz


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