My carbon fiber CNC gantry


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    Default My carbon fiber CNC gantry

    When I mentioned a few months ago that I intended to use carbon fiber to make my gantry, there were a number of people who ask me to provide details of the design and methodology. I am going to use this thread to start sharing info on my progress now that I am little closer to a working prototype.

    This is where I am up to so far with the design and build:



    https://s5.postimg.org/a2fugmklj/IMG_3820.jpg

    My carbon fiber CNC gantry-img_3820-jpg


    The side supports are carbon fiber rectangle tubes at 2" x 6" x 12". The wall thickness is approx 1/2". There is an addition 1/8" steel plate sandwiched between layers of cf on the inside walls to hold screw threads for easy mounting. The void is filled with 1/4" chopped carbon fiber wetted out with resin and high density urethane foam (for "harmonics").

    The main gantry beam is only the front half so far. The part you can see is the face plate which will hold the rails. It's approx 3/4" thick of pure carbon fiber plus an additional 1/8" of thickness from two steel plates sandwiched between layers of cf (to hold screw threads for the rails). When finished, the gantry beam will probably end up around 3x thicker as the rear half has sections of 1" cf tubes embedded at 90 degrees to the rails.

    The gantry face is molded against optically flat mirrors to achieve a perfect mounting surface for the rails.

    Both the gantry beam and the risers use a mix of woven twill weave carbon fiber, non-woven random matrix fabric, tri-axial fabric and chopped 1/4" 12k strands. The directions of the lay up is designed to put all the strength and stiffness where all of the force will come from when in use. Aside from the front two layers of cf, the rest is wetted out with carbon nanotube resin which increases stiffness by an additional 30%. These components are stronger and stiffer than steel, aluminum or titanium etc.

    So far, I had only planned to make the gantry, table and electronics enclosure out of carbon fiber but I might change this soon. I'm feeling a little outdone after seeing an excellent all carbon fiber CNC mill made by a CZ based company. The rest of my frame components are currently all steel and aluminum. I figured that a heavy base frame would be an advantage but as I'm learning... you can always add more weight if needed....

    Anyway... I'll update this thread when I have more progress to report. If anyone has questions or suggestions then feel free. I'll post more info on how the parts are actually made soon.

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    Last edited by Goemon; 07-11-2017 at 07:16 PM.


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    Default Re: My carbon fiber CNC Gantry

    Btw, in case anyone is wondering why we should bother making carbon fiber CNC components, this clip shows why CF is superior to steel and aluminum for applications where strength and rigidity are important:



    I like this clip because it shows a real world example of a steel part vs the same part made out of carbon fiber. It doesn't use theoretical data from charts etc. The CF part is 3 times stronger and noticeably lighter.

    As the forces on CNC components come from predictable directions, I think it could be a great application for carbon fiber. This is especially true for diy builds of benchtop high speed machines where there is potentially a need for components that can be easily moved without sacrificing strength or stiffness.

    Last edited by Goemon; 07-11-2017 at 07:09 PM.


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    Default Re: My carbon fiber CNC gantry

    That video was fairly convincing as to the relative strengths of steel and carbon fiber tube in torsion. But it did mention that the carbon fiber driveshaft was considerably more expensive. Is that because of the expense of the carbon fiber and resins, or the difficulty in working with the stuff? Since you're doing the layup yourself, is your part going to be price-competitive with a gantry made from steel or aluminum? How much time will you have in it by the time you're done?

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    Default Re: My carbon fiber CNC Gantry

    Different applications making a CNC machine, where weight is not an issue, and an aircraft / car where weight is an issue. I've been in the CF aircraft world for 15 years now. It's not something with which I would build a CNC. As for weight, yes CF is superior. As for strength... Depends on your application. One bubble or de-lamination in a shaft and it's garbage. Cost.... THAT'S the fun one. Notice all the equipment used in that shop? Figure a shaft that would ever be used in the CNC world (where are shaft used?) would be 10 - 50 times higher. The logical place to use it is a gantry. BUT, vibration and resonance is something that can drive you crazy, and catastrophically fail, with CF. (That would be adventurous to find the RPM of your spindle and the resonance of the gantry...FYI there are certain aircraft that can not use certain propellers at certain RPMs because they will self destruct when the combination is made?) Structural components for a CF gantry or frame would all have to be hand made. Anything pulltruded would only give strength in tension. Torsion and compression isn't there in a unilaminar part like a pulltrusion. To get any kind of strength you'd be manually laying up parts in molds with bi-directional 90deg / 0deg 45deg / 45deg bidirectional weaves. And even then compression and buckling stinks. Those big 300 foot windmills are generally fiber glass because of these issues. I wish you luck in this adventure.



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    Default Re: My carbon fiber CNC gantry

    I don't question the strength and rigidity, but I think it is more suitable for a 3D printer than a CNC. In a CNC mass is also important and CF is I think far too light, so in the end I am sure that you will need to do something about mass and add some extra weight if you want to machine fast and accurate without flexing due to the forces. I am not sure I'd build a CNC out of CF, but it is an interesting approach and I will follow it up, so keep us updated, please.

    https://adapting-camera.blogspot.com
    https://www.youtube.com/channel/UC_vrAWOz5YGX6_e3qtXg3YA


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    Default Re: My carbon fiber CNC gantry

    Your thread is *extremely* interesting.

    How do You make the CF components ?
    Vacuum, oven, etc ?



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    Default Re: My carbon fiber CNC gantry

    Imo, ime,
    You might be on the edge of a very very successful product, commercially.

    I am the nr 1 advocate for big and heavy. everywhere on the interwebs, but ...
    The only reason is rigidity.

    It is, in theory, perfectly feasible to build more rigid//stronger assemblies in CF.
    If You succeed, tens of millions of $$ are in reach, within a year.

    There are endless numbers of commercial industrial CNC builders, who will happily work with this, if properly presented and sold.
    I wish You the best of luck.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by awerby View Post
    That video was fairly convincing as to the relative strengths of steel and carbon fiber tube in torsion. But it did mention that the carbon fiber driveshaft was considerably more expensive. Is that because of the expense of the carbon fiber and resins, or the difficulty in working with the stuff? Since you're doing the layup yourself, is your part going to be price-competitive with a gantry made from steel or aluminum? How much time will you have in it by the time you're done?
    Imo carbon fiber parts are more expensive because current manufacturing methods are very inefficient compared to other mass production processes. I find it to be more comparable to the price of custom one-off or low volume aluminum or steel parts.

    I know of two companies that make and sell carbon fiber CNC gantries and both have come up with a more automated approach. One mills cf parts from sold blocks and the other uses filament winding. Check out this company: Compo Tech:

    http://cz.compotech.com/vrobky_a_apl...ing_components

    They have some info on the benefits of their carbon fiber CNC gantry beams and how the costs compare to the steel parts they replace.

    The cost of making the cf CNC components yourself is not prohibitive for a diy build. I was not able to find any ready made aluminum or steel gantry components that were anywhere close to being as strong for the same or less money. This was my main motivation. I don't have a large budget but I want high quality and strong components. If materials are chosen wisely it can be a very cost effective alternative to some of the diy metal CNC components available on eBay or CNC stores.

    The level of difficulty involved in making simple shape cf parts like a gantry is very low compared the the cf rifle stocks I usually make. I don't know exactly how long I have spent so far because I do it in my spare time bit by bit. I doubt it is any more than a few hours of actual work though . I also doubt I could make a steel or aluminum gantry from scratch any quicker (or cheaper).

    It is also worth noting that, because I have already made the molds, it would be even quicker and cheaper if I made a second or third part.



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    Default Re: My carbon fiber CNC Gantry

    Quote Originally Posted by warrenb View Post
    Different applications making a CNC machine, where weight is not an issue, and an aircraft / car where weight is an issue. I've been in the CF aircraft world for 15 years now. It's not something with which I would build a CNC. As for weight, yes CF is superior. As for strength... Depends on your application. One bubble or de-lamination in a shaft and it's garbage. Cost.... THAT'S the fun one. Notice all the equipment used in that shop? Figure a shaft that would ever be used in the CNC world (where are shaft used?) would be 10 - 50 times higher. The logical place to use it is a gantry. BUT, vibration and resonance is something that can drive you crazy, and catastrophically fail, with CF. (That would be adventurous to find the RPM of your spindle and the resonance of the gantry...FYI there are certain aircraft that can not use certain propellers at certain RPMs because they will self destruct when the combination is made?) Structural components for a CF gantry or frame would all have to be hand made. Anything pulltruded would only give strength in tension. Torsion and compression isn't there in a unilaminar part like a pulltrusion. To get any kind of strength you'd be manually laying up parts in molds with bi-directional 90deg / 0deg 45deg / 45deg bidirectional weaves. And even then compression and buckling stinks. Those big 300 foot windmills are generally fiber glass because of these issues. I wish you luck in this adventure.
    It's also nice to talk to another carbon fiber guy. Making plane parts is on a different level of quality control requirements...

    My understanding of the problem with cf propellers in planes is with birds hitting them. Apparently there was a failure with a Rolls Royce engine in the early days of cf use when they hit a few birds at high speed and broke them. Cf doesn't have that type of strength. You wouldn't want a cf bullet proof vest, for example. Fiberglass isn't as strong or stiff but it bends more before it breaks which is useful for a thin part like a propeller but not in a gantry where stiffness is key.

    Filament winding is a good method of automating cf production for large companies for simple parts. I believe that the drive shaft in the video was wound and if the weave pattern is chosen correctly, it should pack all the same (or greater) strength that you get from hand laying woven fabrics. It's not something I would set up at home or in a small shop though.

    The point you made about the weave directionality is the right one. It is key to be able to predict the direction of the force so you can specify parts to be strong in the right places. I guess I'll find out if I am correct but I believe that the forces subjected on a CNC gantry to be fairly predictable. My lay-up plan should cover it quite well. If not, I will use my molds again with an improved lay up plan.

    I am looking forward to testing my ideas for vibration control. Apparently steel and aluminum are some of the worst materials for preventing vibration. This is why granite, resin and even cast iron is chosen over steel for machine bases. In theory, a well designed cf part should provide superior vibration dampening than equivalent steel or aluminum components.

    I have a small amount of experience with this type vibration dampening design from the stocks I make. Harmonics is important for precision rifle stocks so I experiment with different fillings to see what works. As you know, a hand laid woven dimensional cf part is typically hollow. To improve harmonics without a significant increase in weight, I sometimes use urethane foam.

    Reducing weight in an CNC gantry is less of a priority so I can experiment with a broader range of materials. I have left space in the cavity to test urethane rubber fillings, silicone rubber, water, oil, sand, gravel, epoxy resins, urethane plastics and granite.

    I also have a bunch of sound dampening materials to try from my home theater business. I have plans to make a sound proof enclosure for my CNC machine eventually because I have sensitive hearing. Part of sound dampening is about vibration so there could be some additional potential.


    On the "cf might be too light for CNC" thing, it is worth stating a couple of key points:

    While CF parts can be lighter with the same strength, they can also weigh the same while being a lot stronger.

    It is a lot easier to add additional weight to a part that was too light than it is to solve the opposite. In other words, if my CF gantry turns out to be too light, I can simply make it heavier.

    Overall Machine weight is less of an issue for high speed benchtop CNC routers cutting soft materials. It is apparently more important for low speed milling machine that cut steel with larger diameter end mills.

    As I mentioned before, I know of two companies that already make and sell CF CNC gantry beams and one already made a successful all carbon fiber CNC mill. This means that for any potential problem, there is almost certainly a solution.

    In most cases I can get the benefits of other materials by adding them to the part. For example, the steel plates sandwiched in my gantry beam to hold screw threads.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by hanermo View Post
    Your thread is *extremely* interesting.

    How do You make the CF components ?
    Vacuum, oven, etc ?
    These particular parts were hand laid in molds and compressed (in between male and female molds) under a vacuum. I use other methods too, depending on what I am making. I have a curing oven which is large enough for my gantry. I will probably use it to cure the final part when I'm done messing with the design.

    The shapes of my gantry components are all simple enough that they could be made by anyone without any expensive equipment.

    I like compression molding for parts that need to be as stiff as possible. You get a much better level of compression that using a vacuum alone.

    The front surface plate for the gantry beam was made under pressure between two optically flat mirrors. I wanted to avoid the need for leveling resins to achieve a flat mounting surface for rails.

    Most of the skill required is in material selection of designing the lay-up path for max stiffness.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by hanermo View Post
    Imo, ime,
    You might be on the edge of a very very successful product, commercially.

    I am the nr 1 advocate for big and heavy. everywhere on the interwebs, but ...
    The only reason is rigidity.

    It is, in theory, perfectly feasible to build more rigid//stronger assemblies in CF.
    If You succeed, tens of millions of $$ are in reach, within a year.

    There are endless numbers of commercial industrial CNC builders, who will happily work with this, if properly presented and sold.
    I wish You the best of luck.
    It has already been done unfortunately. I guess there might be some benefit to creating a made in America version as the existing players are in Europe.

    I wouldn't mind offering some to the diy benchtop market as nobody is doing that yet.

    I had a similar understanding to what you said about the requirement for weight being linked to rigidity. I.e. More weight mean thicker steel which is more rigid and stable.

    CF doesn't have to weigh less than steel though. It can offer greater strength and rigidity at the same weight. It also has other potential upsides such as no residual stress from welding joints, less vibration, greater heat stability, no rusting etc.

    A CF gantry with a granite or epoxy granite machine base has exciting potential for me. In my head, that is what I am working towards. That plus a well sound proofed enclosure.

    For hobby machines, greater portability without loss of strength could be a plus too. it's hard for some people to carry a 300lb machine down into their basement...



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    Default Re: My carbon fiber CNC Gantry

    Thanks again for the posts, I find this very interesting to say the least.

    Quote Originally Posted by Goemon View Post
    It's also nice to talk to another carbon fiber guy. Making plane parts is on a different level of quality control requirements...

    My understanding of the problem with cf propellers in planes is with birds hitting them. Apparently there was a failure with a Rolls Royce engine in the early days of cf use when they hit a few birds at high speed and broke them. Cf doesn't have that type of strength. You wouldn't want a cf bullet proof vest, for example. Fiberglass isn't as strong or stiff but it bends more before it breaks which is useful for a thin part like a propeller but not in a gantry where stiffness is key.

    Filament winding is a good method of automating cf production for large companies for simple parts. I believe that the drive shaft in the video was wound and if the weave pattern is chosen correctly, it should pack all the same (or greater) strength that you get from hand laying woven fabrics. It's not something I would set up at home or in a small shop though.
    I think the first problem most of us would have is that our home shops, often very limited shops, aren't really setup to process Carbon Fiber. So that is the first hurdle to overcome.
    The point you made about the weave directionality is the right one. It is key to be able to predict the direction of the force so you can specify parts to be strong in the right places. I guess I'll find out if I am correct but I believe that the forces subjected on a CNC gantry to be fairly predictable. My lay-up plan should cover it quite well. If not, I will use my molds again with an improved lay up plan.
    For a 3 Axis machine it should fairly straight forward.

    I need to ask how do you make a mold accurate enough to mount linear rails or other parts requiring precision? The molds would, to me anyways, would be very expensive if you want to pull out a net shape object. I know back in the day one of our machine suppliers had parts molded out of epoxy granite and the molds where relatively expensive. Understanding how you are creating your molds and the results you are getting would go a long ways to allowing people to understand if this is feasible for a one off project.

    Oh one more question; is the process you are using for the gantry beam requiring an autoclave to cure the parts? I ask because I'm wondering about the viability of room temperature curing epoxies or other resins. Most of us simply don't have the hardware to do an autoclave like cure.
    I am looking forward to testing my ideas for vibration control. Apparently steel and aluminum are some of the worst materials for preventing vibration. This is why granite, resin and even cast iron is chosen over steel for machine bases. In theory, a well designed cf part should provide superior vibration dampening than equivalent steel or aluminum components.
    This is an age old problem which is often solved by throwing lots of mass at a project. Of course these days there are more tools available to model how and where to put materials to control vibration.
    I have a small amount of experience with this type vibration dampening design from the stocks I make. Harmonics is important for precision rifle stocks so I experiment with different fillings to see what works. As you know, a hand laid woven dimensional cf part is typically hollow. To improve harmonics without a significant increase in weight, I sometimes use urethane foam.
    Do you have a link that covers your stock making enterprises? I can't spend 24/7 thinking about machines.
    Reducing weight in an CNC gantry is less of a priority so I can experiment with a broader range of materials. I have left space in the cavity to test urethane rubber fillings, silicone rubber, water, oil, sand, gravel, epoxy resins, urethane plastics and granite.
    A lot of research already exist with respect to vibration control.
    I also have a bunch of sound dampening materials to try from my home theater business. I have plans to make a sound proof enclosure for my CNC machine eventually because I have sensitive hearing. Part of sound dampening is about vibration so there could be some additional potential.


    On the "cf might be too light for CNC" thing, it is worth stating a couple of key points:

    While CF parts can be lighter with the same strength, they can also weigh the same while being a lot stronger.

    It is a lot easier to add additional weight to a part that was too light than it is to solve the opposite. In other words, if my CF gantry turns out to be too light, I can simply make it heavier.
    I think there are a couple of issues going on here when people suggest the importance of mass.

    Adding mass will often add strength, for instance going form a 1/4" thick tube to a 1/2" steel tube doubles the mass but the thicker walls also impact strength and the way the tube resonates. Sometimes the confusion, at least in my mind, is that mass solved a specific problem. The reality is a bit different in my mind.

    Second Mass in the wrong place is just a waste of resources. This is probably more important in a long production run of a given machine than the common one off machines often discussed here.

    Third mass offers a lot of inertia which solves a slightly different problem.
    Overall Machine weight is less of an issue for high speed benchtop CNC routers cutting soft materials. It is apparently more important for low speed milling machine that cut steel with larger diameter end mills.
    Considering guys get perfectly acceptable results with wooden CNC machine I'd have to agree to an extent. There are however a wide range of performances that people would consider to be acceptable.
    As I mentioned before, I know of two companies that already make and sell CF CNC gantry beams and one already made a successful all carbon fiber CNC mill. This means that for any potential problem, there is almost certainly a solution.
    It still comes down to economics. If they have a machine that ends up accepted in the marketplace then CF machine tools will be a success. For the DIY crowd all we really need is a process that delivers an acceptable result at a reasonable cost delta. Cost is the thing that really bothers me about carbon fiber.
    In most cases I can get the benefits of other materials by adding them to the part. For example, the steel plates sandwiched in my gantry beam to hold screw threads.
    One issue with working with alternative materials is the screwing around with threads( pun intended). I still have a hard time seeing how drilling and tapping a plate that then has to be embedded in a CF structure is time and cost effective against simply drilling and tapping a steel beam. In a production environment I might be able to see it being cost effective but for the "one off" crowd I have a harder time understanding cost effectiveness.

    In any event keep up the posting, I'm learning a lot and might have change of tune once you machine comes online.



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