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  1. #13
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    Default 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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    Default 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?

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

    I'm really looking forward to following your build.



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    Default 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.



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    Community Moderator ger21's Avatar
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    Default 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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    Default 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!

    Last edited by ack1; 07-15-2017 at 04:54 AM.


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    Default 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...

    [FONT=Verdana]Andrew Werby[/FONT]
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    Default 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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    Default 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.

    Last edited by Goemon; 07-15-2017 at 06:07 PM.


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    Default 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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  11. #23
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    Default 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".



  12. #24
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    Default 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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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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