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  1. #1
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    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




    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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    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:

    https://m.youtube.com/watch?v=hjErH4_1fks

    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.

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    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?
    Andrew Werby
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    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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    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.

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    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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    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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    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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    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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    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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    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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    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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    Re: My carbon fiber CNC Gantry

    Wizard, see the answers below. I didn't add your text as a quote as it would get too long but I think I covered all of your questions.

    One of the great things about working carbon fiber and fiberglass for a diy fan is that you don't need to do or buy much to be "set-up" for it. You certainly could invest in expensive equipment but for the majority of small users, it is a case buying raw materials and hand work.

    If you want to use a vacuum bagging process, you can find a used Thomas oil free vacuum pump on eBay for as little as $40. You can manage without one too, for simple parts like these.

    Making a mold accurate enough for linear rails is achieved in two ways. First, you start off with an accurate plug. This is the master shape you use to make the mold. If it has a perfectly flat surface, then the mold surface will mirror it. This is why I chose to use an optically flat mirror as a master for my gantry face plate. No additional work is required to flatten it.

    Second: you need to make your mold out of something that will not warp or shrink. I had this issue in the early days of making rifle stock molds or molds for anything that is long and thin. If you use the wrong material, they bow over time and the two halves don't fit together properly etc. now I make my molds out of carbon fiber non-woven strands with epoxy resin. I use an epoxy gel coat for the mold surface and the combo is perfect. It hardly shrinks or flexes at all. It's the best low cost alternative I have found to paying a fortune for machined aluminum tooling.

    Avoid fiberglass, urethane resin or epoxy putty molds for anything that needs to be perfectly flat and stiff.

    As an FYI, my preferred surface material for molds is the "epoxy black surface coat" sold by ACP Composites. They sell it in quantities as low as one quart so it's great for home use. I bought my last roll of non-woven carbon fiber thick random matrix fabric remanants from Composite Envisions. I got more than 4 yards of thick 50" fabric for less than $20. I also got 2lb bags of 1/4" chopped cf off eBay for less than $30.

    I made my first lot of molds for this project with less than $20 worth of materials. I'll post pics when I get home.

    The processes I use certainly don't require an autoclave or even a curing oven (they are two different things). Using room temp resin will work fine. There are some room temp resins that have higher temp resistance. I would favor one of those to avoid any distortion under heavy use. Both ACP composite and Composite Envisions sell a high temp resistance resin that cures at room temp.

    As an FYI, most small shops make their own curing ovens if they want to heat cure. It's a relatively simple diy project for people looking to get into carbon fiber as more than one-off. Much easier than building a CNC machine. I made my first one using parts fro ma toaster over, high temp insulation and aluminum (extrusion frame and plate for the walls).

    I don't sell my cf stocks through a website or anything like that. I have kept it word of mouth because I can't keep up with demand. This is why I started the CNC project. I can post some pics when I get home later if you want to see some though.

    I understand broadly that just adding more mass does not necessarily help vibration dampening (or anything else). It was more a response to the concern some people raise about cf being potentially "too light". For me, any issues caused by a lack of weight are easy to solve by adding more. I.e. It's not a concern for me.

    I have seen that there is a lot of research on general vibration dampening in the machine world. I couldn't find much on carbon fiber specifically, except the vague general comments about it having superior properties to steel and aluminum in this respect.

    What you said about there being a wide range of performance expectations is so true. I don't need 0.0001 tolerances for any of my businesses. I also keep reminding myself that I am going to start off with a $300 2.2kw Chinese spindle, not a $3,000 European precision piece, so I have some expectation setting of my own to do. For some people, any Chinese spindle is nothing but trash-can food. For others, a $100 router from Home Depot works just fine.

    I just want to build the best machine frame and mechanics I can so I can benefit if I upgrade my spindle in the future. The advice I got repeatedly on this forum was the machine needs to be rigid to work well / with accuracy.

    I can understand why cost would be the number one concern with carbon fiber for a diy fan. Ready made cf parts cost a fortune so it has a rep. To be clear, I am not suggesting that everyone should start using it instead of aluminum for their builds. I am only saying that I believe it can be a viable option for the right type of user in a diy build.

    I have cost concerns with a lot of the options with CNC builds, not just cf. I found it to be a difficult market to navigate without help from the forum. There are a lot of very expensive but low quality components for sale to the diy market and very few reasonably price quality parts available. If you want or need something better than these thin aluminum plate parts, and you have a tight budget, you are going to need to make them yourself.

    Drilling and tapping a cf gantry with a steel plate sandwiched in would take no more or less time than drilling and tapping a steel beam. The purpose of adding some thin metal plates is only to hold the screw threads. Carbon fiber doesn't thread well. The steel would only make up a small percentage of the mass and strength. It isn't duplication in building materials

    You would never use a 1/8" 2" x 36" steel or aluminum plate as a gantry beam on their own. They wouldn't be strong or stiff enough. Think of them as brackets or connecting plate in the cf part. You don't use a corner bracket because it's cost effective. You use it because it's necessary.

    There are a number of reasons why my gantry is being made of CF instead of pure steel but it isn't about cost. It's mainly about quality. Carbon fiber is stronger and stiffer. It's easier for me to work on. I have no welding skills or tooling to machine steel. It suffers less heat distortion, it's not magnetic, it doesn't rust, it has superior vibration dampening, I can join components without residual welding stress.

    I also like the way carbon fiber looks more than steel. This isn't a huge factor but as this machine is going in my home, I would prefer a more stylish appearance if I have a choice and all else is equal.

    I should point out that I am using steel and aluminum for some of my frame components too. It's not like I am building an all cf CNC mill like those Compotech guys. Not yet anyway.

    When you build your own components, all materials have pros and cons. I firmly believe that the best builds will come from the materials people are most comfortable working with. If you have a lot of welding experience, you might be best making a welded steel frame. I have never welded anything in my life. I don't have a clue how I would achieve an acceptably flat surface on steel tube or plates but I know how to make carbon fiber parts. The most cost effective for me is the build I get right first time. Wasted materials is always my biggest cost in a diy project.... (I screw up a lot).

    When I am done and happy with how it all works, I might recruit a few people from here to test a CF gantry so they can report back on how it compares to their steel or aluminum components. It would provide a more interesting perspective as I won't have much to compare it to here.

    I always enjoy hearing people's reaction the first time they hold a well made carbon fiber part. It feels strange to hold something so strong when it feels so light. There is a great company called AG Composites who sell a cf M1a stock. They have a video on their site where they drive a large SUV over it to demonstrate how strong and stiff it is because it's the only way they can explain to people how strong these parts really are. It's like magic... or something...

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    Re: My carbon fiber CNC gantry

    I admit I'm intrigued by the idea of a carbon fiber gantry beam. That's a part in which weight is a crucial factor, and stiffness is key. I wonder how hard it would be to cast my own; I was thinking about cutting a mandrel out of foam and wrapping it with the fiber, but was wondering if it was flexible enough for that to work. That would have the advantage of making the whole part in one go, instead of having to lay up two halves and connect them somehow. But it would then need to be faced with a dead-flat piece of something, either steel, aluminum or cast resin, so I could mount my rails. There's also the issue of mounting the ball screw. With a steel beam, that's not too hard; you can weld in attachments for the bearings at either end, but with carbon, pieces would need to be cast to fit and then glued in. I was also wondering if fiberglass cloth would work about as well as carbon fiber (and cost a lot less).

    What would you charge to make a carbon fiber beam that was, say, 8" tall, 4" wide, and 72" long, flat one one side?
    Andrew Werby
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    Re: My carbon fiber CNC gantry

    I'm really looking forward to following your build.

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    Re: My carbon fiber CNC gantry

    Quote Originally Posted by awerby View Post
    I admit I'm intrigued by the idea of a carbon fiber gantry beam. That's a part in which weight is a crucial factor, and stiffness is key. I wonder how hard it would be to cast my own; I was thinking about cutting a mandrel out of foam and wrapping it with the fiber, but was wondering if it was flexible enough for that to work. That would have the advantage of making the whole part in one go, instead of having to lay up two halves and connect them somehow. But it would then need to be faced with a dead-flat piece of something, either steel, aluminum or cast resin, so I could mount my rails. There's also the issue of mounting the ball screw. With a steel beam, that's not too hard; you can weld in attachments for the bearings at either end, but with carbon, pieces would need to be cast to fit and then glued in. I was also wondering if fiberglass cloth would work about as well as carbon fiber (and cost a lot less).

    What would you charge to make a carbon fiber beam that was, say, 8" tall, 4" wide, and 72" long, flat one one side?
    The process you are asking about is typically referred to as "skinning" or "wrapping". I would advise against it for this type of part. It's usually used for cosmetic pieces where people just want the carbon fiber look. The more layers you add, the more problems you will have keeping it flat and smooth. If you just cure one side against a flat surface, the fabric will sag on the side walls and look unsightly.

    It might sound easier but I have always found skinning to be more difficult than making a part properly in a female mold. Skinning with large flat parts (like a gantry beam) presents all kinds of difficulties that would result in wasted materials for a newbie. For one, the material needs to be held perfectly flat against all sides of the part in the center (the male mold). If you use a vacuum bag for that, it will leave wrinkle marks on the surface you wanted to be flat. If you try and do it with enough layers to make it strong, it will be even harder to hold it flat (like folding a phone book).

    Embedding metal plates to hold screw threads would be even more difficult with skinning. If you have to go that route, use a metal center and round off all the corners. Cf does not like 90 degree angles. Wrapping a rounded shape will be easier. Wrap the outside in a smooth release film and tape it tight for curing. You'll have to squeegee out the trapped air between the cf and release film to achieve a smooth finish. It will be hard. I would go with a female mold instead....

    Carbon fiber is the least forgiving material I have ever used. Do each step properly so you only have to do it once. It's all the trial and error and wasted materials that racks up the bill and time expended with composites.

    On the other hand, if you spend the time upfront getting the mold right, it's usually fairly easy and quick after that. Don't be afraid of making a mold. If you use the materials I recommend, it's not difficult or expensive for simple shapes like these. Once you have a mold, you can use it to make multiple identical parts too. The gantry risers, for example will benefit from this. You will never achieve uniform size on both sides by skinning two separate risers. Parts from a female mold are uniform in size.

    You might also want to make a second CNC machine at some point, or build a 3D printer, or decide that you need to remake your gantry with stronger materials, or maybe you want to share the upfront cost with a friend so you need to build two gantry beams etc. it's always good to have the mold. Without it, one mistake means starting all over again.

    Anyway... if you wanted to try making a CF part, this is a good first project. It is realistically achievable for a determined and enthusiastic diy fan. Plus, there is a lot of potential uses for strong cf beams like this. I am already using my molds from this project to make an attractive electronics enclosure for my gecko and legs for a machine stand in my garage.

    If you do decide to try making a cf part, make sure to buy a quality respirator. A $5 disposable dust mask is not sufficient. Carbon fiber is not toxic but you don't want to be inhaling the dust when you sand it. This is extremely important.

  17. #17
    Community Moderator ger21's Avatar
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    Re: My carbon fiber CNC gantry

    Care to share some pictures of your molds?
    And where do you get the optically flat mirror?
    Gerry

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    Re: My carbon fiber CNC gantry

    This is really interesting. I have a Multicam router with 2x3 meter work area so the gantry is very long and flexes if i engrave too fast so ivve been thinking about how to stiffen it up.

    Will be following closely!

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    Re: My carbon fiber CNC gantry

    I called a carbon fiber supply house yesterday to see if it was possible to use stock beams instead of trying to cast my own. The biggest ones they had in stock were 2" x 4" , which didn't seem sufficient for my design, which has a 6-foot span to cover; I was thinking more like 4" x 8". The person I talked to suggested that instead of trying to glue up 4 of these 2x4s (which cost about $400 each), they could build a beam for me out of flat stock, using carbon angle in the corners. Buy he cautioned me that while it would be considerably lighter than a steel beam, it would be nowhere near as rigid. Apparently carbon fiber is rated at 8,000,000 psi, but steel is 30,000,000. I'm not exactly sure what these numbers represent, but it sounds like steel is about four times stiffer. However, a 4" x 8" steel beam with a 1/4" wall weighs 19.3 lbs per foot, so I'm looking at 116 lbs for the gantry beam alone, before I add end caps, a heavy ball screw and the Z axis assembly with spindle, motor, etc. (not to mention the 5th and 6th axes assembly). I suppose I could use aluminum, but I'd want to go with a thicker wall, which obviates some of the weight advantage. On the other hand, if I was building it out of carbon fiber, I could put stiffeners inside the beam, which would help rigidity. I'm still on the fence here...
    Andrew Werby
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    Re: My carbon fiber CNC gantry

    Quote Originally Posted by ger21 View Post
    Care to share some pictures of your molds?
    And where do you get the optically flat mirror?
    I am writing up a brief tutorial on making the molds (with pics included). I'm nearly done so I will post it here shortly.

    The optically flat mirrors I used were "front surface mirrors" borrowed from an old (and large) rear projection installation. I happen to have access through my other business. They are probably too expensive to buy just for this. I think that for most diy or small shop builds, using regular glass or a quality (rigid) regular mirror would be fine. That is what I would have used if I didn't have access to the front surface mirrors.

    The difference in how flat they are is smaller than you can see. It might make a difference if you are going for the ultimate level of precision but I don't really know for sure. I don't even know how flat my rails really are. I do know that most glass and quality mirrors are flatter than most people could achieve themselves by machining steel or using leveling resins.

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    Re: My carbon fiber CNC gantry

    Quote Originally Posted by awerby View Post
    I called a carbon fiber supply house yesterday to see if it was possible to use stock beams instead of trying to cast my own. The biggest ones they had in stock were 2" x 4" , which didn't seem sufficient for my design, which has a 6-foot span to cover; I was thinking more like 4" x 8". The person I talked to suggested that instead of trying to glue up 4 of these 2x4s (which cost about $400 each), they could build a beam for me out of flat stock, using carbon angle in the corners. Buy he cautioned me that while it would be considerably lighter than a steel beam, it would be nowhere near as rigid. Apparently carbon fiber is rated at 8,000,000 psi, but steel is 30,000,000. I'm not exactly sure what these numbers represent, but it sounds like steel is about four times stiffer. However, a 4" x 8" steel beam with a 1/4" wall weighs 19.3 lbs per foot, so I'm looking at 116 lbs for the gantry beam alone, before I add end caps, a heavy ball screw and the Z axis assembly with spindle, motor, etc. (not to mention the 5th and 6th axes assembly). I suppose I could use aluminum, but I'd want to go with a thicker wall, which obviates some of the weight advantage. On the other hand, if I was building it out of carbon fiber, I could put stiffeners inside the beam, which would help rigidity. I'm still on the fence here...
    It sounds like you spoke to someone who didn't know enough to be giving other people advice. Ignoring the fact that stiffness is not measured like that, his numbers are wrong. Perhaps he was quoting the tensile strength of their beams specifically (as that is measured in PSI) or just as likely, he got it the wrong way round - I.e. Carbon fiber's tensile strength (Howe much it can be stretched before snapping) is 4 x greater than steel. As mentioned here:

    https://arstechnica.com/science/2015...-carbon-fiber/

    Some of the cf I-beams, tubes and channels I see for sale are most certainly too thin and expensive to be a viable alternative to steel. In general, cf doesn't like long flat parts with 90 degree angles so a CNC gantry requires more design thought.

    A properly designed carbon fiber part will be stronger and stiffer than the equivalent steel. "Properly designed" is the key point with carbon fiber parts. It makes far more of a difference than it does with metals. A part is not automatically stronger, stiffer or lighter just because it's made of carbon fiber. It is definitely possible to make a weaker part. An aluminum plate can be stronger than steel if it's 5" thick and the steel is 1".

    For example of how important cf design is... if you cure a single flat layer of 2x2 twill carbon fiber, you can bend it and tear it with your hands. You cure that same piece of cf in a tube shape, you would struggle to bend it at all. If you stood on the end of the tube, it would probably support your weight.

    Where cf has the advantage is that parts can be designed in a way that puts all the strength and stiffness where you need it based on the direction of the forces. As you can see in the video comparing the cf and steel drive shafts. The steel shaft bent and then broke with 1/3 of the force of the cf part. The CF part hardly bent at all before it broke. The cf shaft was designed to take that type of force in that direction.

    The better approach with CF is to start with how much strength and stiffness you need and then specifying the part to deliver that. In a diy environment without engineering expertise (which is most of us here), more trial and error would be involved. I.e. If a part is not strong or stiff enough, you add more layers (in the correct orientation) until it is.

    Personally, I would never buy ready made cf plates, tubes or beams. Most companies over here charge a fortune for very average parts. You'll pay $400 for $50 worth of carbon fiber. The cheapest 1.5" x 48" round tubes on eBay cost over $80. I can make the same tube myself for $15.

    If money is no object and you want to buy ready-made, why not try getting a quote from Comotech? They export directly to America and the rest of Europe. They have specific expertise and experience in designing and building carbon fiber gantry beams for CNC machines. They have the capability to build beams of 12 feet (or even longer). They could make a gantry for you that is stronger and stiffer than a steel one or lighter for the same strength.

    I hate the idea of ordering an expensive custom cf part from someone who doesn't understand what is needed in a gantry or how best to achieve it. Starting with cf angles and flat stock doesn't sound like a good design plan at all. It sounds flimsy. You don't want carbon fiber for the sake of it. You have to design the part properly to get the benefits.

    If it were me, if faced with the choice of paying a fortune for their suggested approach with cf, or using regular steel or even aluminum beams, I would go with the steel or aluminum.

  22. #22
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    Re: My carbon fiber CNC gantry

    Most companies over here charge a fortune for very average parts. You'll pay $400 for $50 worth of carbon fiber. The cheapest 1.5" x 48" round tubes on eBay cost over $80. I can make the same tube myself for $15.
    The need to make money always makes things cost more.
    If it cost me $15 and an hour of my time to make that tube, I'd certainly be selling it for at least $80.

    The real cost savings here comes at the expense of your time.

    I'm building a large machine from wood, using a lot of very time intensive techniques. So, it's very inexpensive, but takes a lot of my time. I think carbon fiber construction is similar.
    Gerry

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    Re: My carbon fiber CNC gantry

    Quote Originally Posted by ger21 View Post
    The need to make money always makes things cost more.
    If it cost me $15 and an hour of my time to make that tube, I'd certainly be selling it for at least $80.

    The real cost savings here comes at the expense of your time.

    I'm building a large machine from wood, using a lot of very time intensive techniques. So, it's very inexpensive, but takes a lot of my time. I think carbon fiber construction is similar.
    Can't argue with that. Just like building a CNC machine, there is a huge saving if you do it yourself ( and a lot of satisfaction). I feel like cf parts and CNC machines seem to have much higher margins than most other businesses.

    I don't think it's all justified by labor costs though. When I make a cf rifle stock, that is a really time consuming lay-up with a lot of difficulty plus high wastage costs. There are good reasons for the high prices charged by companies like Manners and McMillan. With things like the simple round tubes, it's just pure profiteering sometimes.


    Making my own cf round tubes and plates was the first thing I learned. It's very easy and not time consuming at all.

    I feel the same about some of the CNC mechanical kits where people are charging $1500 for $300 worth of aluminum extrusions, plates and screws. Some people think "great, they've done the work for me", diy fans like us think "what could I build for than cash if I do it myself and put their profit margin towards superior components".

  24. #24
    Community Moderator ger21's Avatar
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    Re: My carbon fiber CNC gantry

    My biggest issue with most CNC parts and kits for sale, is that the people selling them don't know what they are doing in most cases. Not only can you usually build the same thing for less money, in most cases, you can build something better for less money.
    Gerry

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    Re: My carbon fiber CNC gantry

    Quote Originally Posted by ack1 View Post
    This is really interesting. I have a Multicam router with 2x3 meter work area so the gantry is very long and flexes if i engrave too fast so ivve been thinking about how to stiffen it up.

    Will be following closely!
    What is the gantry made of and what are you cutting when it flexes?

    Those Multicam branded machines look well made in the pics. The gantry beams look thick, it's surprising that flex would be a noticeable issue.

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