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    Default Re: My carbon fiber CNC gantry

    Goemon wrote:

    "When I am satisfied that my design works and is worth sharing, I'd be tempted to use my mold to make another for someone else here to test. Ideally, someone with a comparable size steel machine. I would certainly like to know if it allows people to take deeper cuts or achieve better tolerances etc. I suspect that there would be too many variables to make useful comparisons though."

    I might take you up on that. How long is that gantry? I was planning on about a six-foot span (I've already got a ball screw that long), but my plans are still in flux at this point. What would you charge for another beam out of that mold?

    [FONT=Verdana]Andrew Werby[/FONT]
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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by awerby View Post
    Goemon wrote:

    "When I am satisfied that my design works and is worth sharing, I'd be tempted to use my mold to make another for someone else here to test. Ideally, someone with a comparable size steel machine. I would certainly like to know if it allows people to take deeper cuts or achieve better tolerances etc. I suspect that there would be too many variables to make useful comparisons though."

    I might take you up on that. How long is that gantry? I was planning on about a six-foot span (I've already got a ball screw that long), but my plans are still in flux at this point. What would you charge for another beam out of that mold?
    It's 48" long, 8" tall and 8" thick so it's a few feet shy of what you're looking to build. Also, the gantry risers are both 6" wide so the "portal" under the gantry beam is only 36". I am making the machine specifically for molds that are 30" x 8" max.

    it's a chunky design for making parts that small but everyone told me that it had to be as stiff as possible to machine aluminum well...

    It wouldn't be that hard for me to make a 6 foot cf gantry beam but I am just not set-up to handle parts that large here yet. Also a part that large would be a fairly sizeable investment for a diy project just in materials. That's the sort of part size those Compotech guys make using their CNC lume and robotic filament winder.

    - - - Updated - - -

    Quote Originally Posted by awerby View Post
    Goemon wrote:

    "When I am satisfied that my design works and is worth sharing, I'd be tempted to use my mold to make another for someone else here to test. Ideally, someone with a comparable size steel machine. I would certainly like to know if it allows people to take deeper cuts or achieve better tolerances etc. I suspect that there would be too many variables to make useful comparisons though."

    I might take you up on that. How long is that gantry? I was planning on about a six-foot span (I've already got a ball screw that long), but my plans are still in flux at this point. What would you charge for another beam out of that mold?
    It's 48" long, 8" tall and 8" thick so it's a few feet shy of what you're looking to build. Also, the gantry risers are both 6" wide so the "portal" under the gantry beam is only 36". I am making the machine specifically for molds that are 30" x 8" max.

    it's a chunky design for making parts that small but everyone told me that it had to be as stiff as possible to machine aluminum well...

    It wouldn't be that hard for me to make a 6 foot cf gantry beam but I am just not set-up to handle parts that large here yet. Also a part that large would be a fairly sizeable investment for a diy project just in materials. That's the sort of part size those Compotech guys make using their CNC lume and robotic filament winder.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by jono5axe View Post
    Very interesting thread for me, as I am just about to build a 4000mm long composite gantry. I have been procrastinating back and forth about it, and maybe just to use steel, but am pretty committed by now to doing it in composite. I therefore list my plan below, for the purpose of getting everyones comments. All comments and ideas gratefully accepted - to ensure I am not overlooking something....

    - Composite gantry beam 4000mm long x 600mm high x 400mm deep [RHS - rectangular hollow section].
    - Construction: Sandwich construction - 5mm foam core, internal laminate = 2mm quadraxlial glass fibre, external laminate = 4mm quadraxial carbon fibre & glass fibre (50%/50%), with transverse internal gussets/bulkheads every 300mm (bonded in).
    - Resin system = epoxy, infusion, room temp.
    - Method: vacuum infusion + hotbox post cure cycle. [make up core material as C-Section, lay-up inside C-Section, bond in transverse gussets, close C-Section by bonding on last side panel, vacuum infuse external laminate in one hit].
    - Thermal expansion goal is to achieve approximate equivalence with concrete [13x10-6 m/(mK)] and steel [12x10-06 m/(mK)], as side frames are steel and machine base is concrete floor. Thermal expansion co-efficient of epoxy GRP = 36x10-06 m/(mK), epoxy/carbon = 2x10-06 m/(mK).

    Metal threads will be achieved by either/or
    1) 50x8mm steel flatbar laminated into the core of the sandwich construction, or,
    2) Drilling beam and bonding in threaded inserts (with plexus/crestabond/etc)

    Datum faces (machine beds) for 35mm linear rails & 24x24mm gear rack will be produced by one of the following methods, either/or:
    1) Shimming components in place and then back-filling gaps with "Chock-it" [CHOCKFAST ORANGE (PR-610TCF)], or,
    2) Epoxy-concrete machine beds, molded on a 4000mm long flat table produced with self-leveling epoxy (make flat table mold using self-leveling epoxy, lay in the epoxy/sand/fibre mix on the table mold, place the gantry beam on top to bond the epoxy concrete machine beds to the beam.

    ??? forgotten something?...

    Like I said, all comments and ideals thanks very much.

    Regards,
    Jono
    I am tempted do do a quick FEA on this beam, to see how it would compare with a steel beam ito stiffness and mass, and also to see what the effect would be to use more UD on the outside to decrease the carbon and use it more efficiently. That quad carbon/glass hybrid fabric seems appropriate to use in something like a boat hull, but in a highly predictable structure like a gantry beam, I suspect you can do better by using the fibres carefully.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by drieslaas View Post
    I am tempted do do a quick FEA on this beam, to see how it would compare with a steel beam ito stiffness and mass, and also to see what the effect would be to use more UD on the outside to decrease the carbon and use it more efficiently. That quad carbon/glass hybrid fabric seems appropriate to use in something like a boat hull, but in a highly predictable structure like a gantry beam, I suspect you can do better by using the fibres carefully.

    We will real-world-know about the gantry beam performance pretty soon, as the buiuld is coming along.

    I have started a build thread at http://www.cnczone.com/forums/cnc-wo...neering-3.html

    It is going a bit slower than planned, but it is coming together. I need to post some more progress pics.....

    J.

    Jonathon Clarke
    www.solpont.com


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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by drieslaas View Post
    I am tempted do do a quick FEA on this beam, to see how it would compare with a steel beam ito stiffness and mass, and also to see what the effect would be to use more UD on the outside to decrease the carbon and use it more efficiently. That quad carbon/glass hybrid fabric seems appropriate to use in something like a boat hull, but in a highly predictable structure like a gantry beam, I suspect you can do better by using the fibres carefully.

    The design is key when you need max stiffness from a CF part. People desperately want a simple direct comparison with linear materials like steel but, unfortunately, it doesn't work in the same way. It's not a linear material.

    The choice of fabric and the orientation of the lay-up is a key part of the design. As you said, you have predictable directional forces with a gantry beam - which is ideal for CF part designs. You can specifically increase strength and stiffness in the directions needed. A high modulus unidirectional fabric is a good option for this.

    Also, I can't stress enough the importance of the shape to increasing stiffness. This is true with steel too - e.g. You get better stiffness with an I-beam than a flat sheet. The shape matters even more with carbon fiber though, espiecially if your cf part has less weight than the steel one.

    Pound for pound, cf parts have greater strength and stiffness than steel but... if you want the cf part to weigh less and have the same (or more) stiffness, design is key. Obviously, if you have unlimited funds, you can just increase wall thickness of a part until it is strong enough but I am going to assume that most people in the diy section don't have a limitless supply of cash....



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    Default Re: My carbon fiber CNC gantry

    I just happened upon this thread. Very informative. I'm also enjoying Jono5Axe's build thread.

    Goemon - If you are looking to build a lightweight gantry that is also precise, why are you using what look to be supported round rails instead of low-profile rails?



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    Default Re: My carbon fiber CNC gantry

    HI All - Interesting thread. I've been involved with marine and industrial composites for some 30 years. The story told here is a very common one. Especially about sandwich construction. A sandwich should never have been used for a gantry. It needs to be a solid laminate. The manufacturing method described using nomex and the sag in service says to me it's delaminated. A well made composite part would never change shape in service. CF is certainly stiff and we can make laminates as stiff as aluminium but we can't make laminates using readily available CF as stiff as steel. CF is certainly light and damp at 1500kg/m3 so for accelerating tasks it's great. Now to discuss a gantry. A gantry has to be stiff in bending and in shear stiffness (torsion). If you design a laminate to be the same stiffness as aluminium in bending/axial then you have a laminate that is very poor in shear stiffness. AL has a shear stiffness of 27GPa. Its tough to get past G=6-8Gpa in a CF laminate so although you have good bending stiffness you have poor torsional stiffness. To make this up you 2X or 3X the thickness in CF and you are at the aluminiums weight and twice its bending rigidity and twice the cost. So aluminium is the ideal material. Damping strategy has to be better in AL though. Now to take a step back, if you design a mould that incorporates various features like mounts, fittings, tapered parts etc then you win with CF if you are going to make several parts. If you just make a plain shape CF gantry then its debatable about the huge cost difference in the plain section CF vs AL. Currently I pay about $7/kg AUD for aluminium and to buy CF its about $80/kg before processing so its quite a diff. Gaemon you mention HM CF, that places you at a cost point that is quite out of reach for DIY machinery. You also mention glass. If you use glass you can only get to 30GPa inplane and 10GPa in shear. Its not really competitive with AL unless you use very large sectional sizes. A very good laminate is 1800kg.m3 so if you use an "oversize" section you quickly get to aluminium again. Not saying CF is out just need to know a bit more than is presented in this thread. Happy to answer Q's.

    For tool plates and Z axis stuff being small and thick its ideal I think. These move, need to be stiff and need to be shaped for optimum performance. Peter

    Last edited by peteeng; 04-12-2019 at 02:55 AM.


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    Default Re: My carbon fiber CNC gantry

    Thanks Peteeng for the comments. Your engineering back ground pretty much confirms my seat of the pants guesstimate that CF isn’t cost effective for a DIY one off solution.

    You do bring up the idea of custom molds for an optimized structure. The question then becomes how would that sort of approach compete with castings in aluminum or iron which also can be optimized for the application?

    I’m very interested in machine building solutions that can be leverage in a home shop. I’m just having a hard time imagining CF filling that role. To that end do you have any links to web sites covering the production of CF machine tool parts? I’ve pretty much abandoned the idea of using CF but there is a huge appeal to building things with cold processes. That is something easier and safer than melting metal. Maybe CF is simply the wrong material?



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    Default Re: My carbon fiber CNC gantry

    Hello Wizard - If you understand and are good at infusion then CF is ideal for DIY jobs. Infusion provides low resin content (around 28-30% by weight) high fibre volume as good as aerospace and you can make it any shape you want if you make a mould or a plug then a mould and you can make it in your kitchen. If you have a router then you can easily make moulds direct in MDF or plastic. If you hand laminate things you will not get the strength or stiffness that is required for machine parts, may as well stick to aluminium unless you want a shape that you can't machine or bend or you just want to give it a go. I'm all for experimentation and fun. There's a lot of commentary about its stronger and stiffer than steel which is incorrect. The fibre maybe, but the laminate is no where near it. If you make a laminate as good as aluminium in stiffness you are getting near the mark. For flat projects you can make a flat panel and machine it just like metal. F1 call this black aluminium. People also say that there is so much room for optimisation and you can have so many variables and layups. It boils down to two layups is all you need. Do not use woven cloth as it is half the stiffness of straight fibres. Use UD and double bias only.

    For a bending application such as a beam you need a laminate of 25% double bias and 65% UD by weight. The laminate should be well interspersed. It will be stiffer than aluminium (~80GPa) in bending but not as good in shear. It will be stronger than any aluminium alloy you can buy. 7075 about 500Mpa Cf lam about 800Mpa.

    A general purpose laminate would be a balanced quadaxial laminate. It will be 50Gpa. I have been having laminates tested for various reasons for over 20 years so have a good database of results. Good luck Cheers Peter S



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by peteeng View Post
    Hello Wizard - If you understand and are good at infusion then CF is ideal for DIY jobs. Infusion provides low resin content (around 28-30% by weight) high fibre volume as good as aerospace and you can make it any shape you want if you make a mould or a plug then a mould and you can make it in your kitchen. If you have a router then you can easily make moulds direct in MDF or plastic. If you hand laminate things you will not get the strength or stiffness that is required for machine parts, may as well stick to aluminium unless you want a shape that you can't machine or bend or you just want to give it a go. I'm all for experimentation and fun. There's a lot of commentary about its stronger and stiffer than steel which is incorrect. The fibre maybe, but the laminate is no where near it. If you make a laminate as good as aluminium in stiffness you are getting near the mark. For flat projects you can make a flat panel and machine it just like metal. F1 call this black aluminium. People also say that there is so much room for optimisation and you can have so many variables and layups. It boils down to two layups is all you need. Do not use woven cloth as it is half the stiffness of straight fibres. Use UD and double bias only. .
    Peter, I think optimisation/variability is maybe referencing the ability to vary the laminate in specific areas to help with localised requirements, for example bearing/buckling and locations for fixtures etc. Another example would be a simple cantilever beam in pure bending, with higher stress at the base and zero stress at the end, where obviously the laminate thickness can be varied along the beam in proportion to the stress (thick at the base and thin at the end). So, I think the benefits of optimisation/variability are true and relevant.


    Quote Originally Posted by peteeng View Post
    For a bending application such as a beam you need a laminate of 25% double bias and 65% UD by weight. The laminate should be well interspersed. It will be stiffer than aluminium (~80GPa) in bending but not as good in shear. It will be stronger than any aluminium alloy you can buy. 7075 about 500Mpa Cf lam about 800Mpa.

    A general purpose laminate would be a balanced quadaxial laminate. It will be 50Gpa. I have been having laminates tested for various reasons for over 20 years so have a good database of results. Good luck Cheers Peter S
    When I started to consider a build project I read some white papers on machine tool gantry design, some of them linked from this site, if I recall correctly. One of the key takeaways from my reading was that the critical design consideration was deflection in torsion (rather than bending). We discussed this on another thread. I stand to be corrected, but I believe this information stands. Your comments above relating to fibre orientation are considering a gantry beam in bending, so I do not agree with your points, other than using a quadraxial cloth. But, if we do consider bending, and considering our options with optimisation/variabilty, then some unidirectional fibre on the bottom where the max tensile stress due to bending occurs makes sense. That is a good example of the ability to optomise a laminate.

    But this is all over the top for diy router gantries (it is only really important for larger machines) and I think that people should just go ahead and build diy gantries out of hand laminated epoxy and glass fibre (structural cloth, biaxial, double bias, etc, not CSM) and it will work just fine for 5ft long gantries on wood routers. But the question would be why, as steel/aluminum is also fine and fairly simple to build. For larger machines (large/longspan gantries) if weight of the moving parts can be reduced then higher accelerations (read higher performance) can be achieved with smaller (cheaper) drive gear, and the machine design in general can be downsized. So, for weight saved in the gantry and Z-axis the whole machine can be significantly cheaper for the same performance. Or alternatively, the same machine can have higher performance. It is interesting to read some machine manufacturers (with large robust steel gantries) quoted travel figures and then look at their servo specs and realise that there is no possible way the the machine can ever accelerate to that velocity in the length of available travel. So for me, gantry weight becomes more important as the size of the machine increases.

    Interestingly, this tread was originally about a carbonfibre fixed gantry machine.

    Jonathon Clarke
    www.solpont.com


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    Default Re: My carbon fiber CNC gantry

    Hi Jono - Optimisation of a laminate is something that I have been doing for 30 years. It turns out there are only two laminates to consider. A highly UD dominant Triaxial and a Quad, anything else is chasing straws. Obviously the laminate thickness can be varied but only by the module (M) of the laminate. eg depending on what cloth is available you design a module that fits the elastic properties required. This maybe 1mm thick or 4mm thick depends. Then once that module is established you vary each area in a structure by that module. eg 1xM, 3xM, 10xM etc. Your comment about adding UD at the bottom is against all the elastic rules. You made an asymmetric laminate, you screwed up the local elastic properties of the laminate, you made an asymmetric structure. Sorry not the way to go.

    My commentary about CF being poor in torsion does not mean its out entirely. That's like saying steel has poor damping so its off the table for machinery. My prior statements are general comments. Once you commit to CF construction like any other construction domain you make the design work within that domain. Building composite structures is very similar to metal structures but there are some things you do and don't do. Same as if you converted a steel structure to an aluminium structure there are nuances to get the best out of the material and there are some things that work in steel that don't in aluminium. For instance I do not see the point in adding steel backers for threads in composites. Composites like timber take threads very well, they just have to have longer engagement than steel . In all things that move (and stationary objects as well, I was involved in a fibreglass lighthouse a couple of years ago) , cars, bikes, planes & boats over the last 20 years they have gone from steel to aluminium to composites. This will happen and is happening in machine design as well.

    I think that at a DIY level hand laminating FG results in poor stiffness and may as well go with aluminium unless its a shape that is impossible to do with aluminium. I'm all for people doing stuff and I'm sure hand laminating has a place in the DIY world. People build machines from all sorts of stuff for all sorts of reasons that baffle me, but hey as long as they have fun doing it that's great by me as well. But if you are trying to make a very stiff machine especially at a commercial level you need to make every post a winner. Cheers Peter S



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