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Thread: My carbon fiber CNC gantry

  1. #61
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    Default Re: My carbon fiber CNC gantry

    Hi Wizard ,
    Sorry to confuse you , I figured someone wanting to build a carbon gantry may have a broad understanding of the process and components . That said , I will explain .
    Hybrid laminates are a mix of various materials like carbon/kevlar or carbon /S or E glass . There are many different hybrids and these address various aspects where for instance carbon /kevlar would be used where both stiffness and impact resistance is needed . Remember these cloths are a mix of properties , so do a little of each .
    The different weaves where developed for lay or how the cloth drapes on a plug or in a mold , say for instance unidirectional cloth does not like to take a tight turn in length ,but a twill weave at 0/90 or +45-45 would lay much better . These weaves can also add to the stiffness of the component being fabricated .
    Cross linked resins are not that new and in the case of polyester resin it's the isopthalic polyester where non cross linked is orthopthalic polyester . A cross link is a much stronger bond on a molecular level so makes for a stronger resin .
    This cross linking has been used in epoxy development where the molecular chain has been altered in a way that it betters certain properties .
    Proset epoxy is a Gougoen Brothers product ,the makers of West Epoxy and is a cross linked epoxy . It is used by a lot of high end custom boat builders these days because of its broad properties ,like it makes a very good infusion resin with a 9 hr pot life and it can be used for wet layup with a brush and roller with the use of a different hardener . The various other manufacturers have their own take on these various resins including System Three .
    For something like a self built gantry ,using prepreg or high temp cure resins is cost prohibitive and the amount you win by going this route is not the same as the substantial investment made in the purchase as these components can cost substantially more .
    Post curing helps remove any volatiles left in the resin after the initial cure . These components are usually solvents or plasticizers which can soften the resin if left behind making for a weaker bond . The post cure process is usually a uniform heating up of the component to help the off gassing of the volatiles . Most components continue to off gas over its lifespan and some polyester race boats that where post cured 15 years ago still offgas the strong MEK smell if drilled or cut into . The same for some of the solvent based epoxy boats built years back .
    Post curing can distort a component if it is not properly supported so a lot are post cured in a mold or on a plug under vacuum .
    A lot of the low temp cure resins are being used now for less distortion and will cure at temps between 160 -180 Fahrenheit which is attainable with a propane space heater in a plastic tent or a hotbox made from polyiso insulating foam sheets like sold at Home Depot .
    The best way to go is to actually call all the various suppliers and tell them what you want to achieve and ask what product they would suggest you use . These guys work with all these component daily and most are aware of what works and what doesn't . Collect as much info as possible ,then make a decision which way you want to go . If this is not your everyday job ,I suggest to do a test patch first to get familiar with the process and the workability of the components . Do a small section in the mold with the full layup you have calculated to work and see what it takes to do the job . If possible work in an air conditioned room and use slow set hardener for a longer pot time , so you have ample time to fix any holidays or wowies you may make .
    The use of a vacuum bag will also help hold things together and can be set up prior to laminating , so it's easy to pull over and seal , then start to pull a vacuum and check for bag leaks . A bag leak will introduce an air source into the laminate and can pull enough resin out of the area to form a dry spot which would destroy the component . Let the resin kick off and while that is happening build your tent or hotbox around the component ready for post cure . Most of the new resins only need a 24 hour post cure with a cold shut off at the end , unlike some of the older resins that required a slow rise and fall with a 48-72 hour cure, this can use a lot of propane if you don't have an efficient oven .
    If you intend to secondary bond anything onto the component , it is a must to use a material called peel ply which is a woven polyester cloth that is draped over the component before the bag goes on . What this peel ply does is pre prep the surface so you don't have to abraid the surface and solvent wipe which can trap solvent in the adhesive . It also allows the amine blush to come to the surface of the peel ply and is removed when you pull off the peel ply .
    Amine blush is a waxy layer created by the reaction during the epoxy cure that floats to the surface ,and needs removing before anything else can adhere to it . It can be removed by washing with soap and water and a light abraiding with a Scotchbrite pad or the use of peel ply .
    Most fabricators will leave the peel ply on until they need to bond as it keeps the component surface isolated from dirt ,they will then mix a batch of adhesive ,pull the peel ply and apply the adhesive and whatever they are bonding . Any masking or setup work can be done around or through the peel ply if necessary.

    I hope this explanation helps you understand a little more and answers some of your question
    Regards Roc



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by jono5axe View Post
    Goemon, I had another thought - re post-cure and epoxy agregates.

    My earlier comments on post-cure relate to laminates, and I am not so sure about the situation with epoxy/aggregate mixtures. I would expect the same to apply in general terms, but possibly to be less important as the quantity and mass of the aggregate fill is so great that it modifies the resin behaviour to an extent (shrinkage, geltime, cure, exotherm, etc). I would expect that post-cure would still be desirable for high tolerance machines, but possibly not very important otherwise. Mild elevated temperatures and time will achieve complete stability sooner or later.

    Jono
    I don't think adding a granite mix or sand will sufficiently change the resins heat deflection temp to mitigate any potential issues from using low quality resins. Other properties can be changed though. For example, I added chemicals to make it flame retardant and carbon nanotubes to increase stiffness.

    I have tried most of the commonly used resin brands and so far Adtech 820 is the best for wet lay ups. It has the highest stiffness and heat deflection temp without any post curing. It's noticeable better than West systems in every way except price. For most people, 180 degrees is probably good enough to use without post curing. For those with curing ovens like me, it can be post cured to 350 degrees giving it similar heat resistance to most heat cure prepregs.

    I make my own prepreg these days and keep it in my freezer ready to use. It's far more cost effective and I get better results than most of the bought-in prepregs I have tried. I recommend it you haven't tried it yet. It changed everything for me.

    I think that heat curing or post curing large parts, such as people building larger CNC machines, is always going to be an issue for hobby users. I own a composites business so it makes sense for me to have a curing oven. I doubt I would want a large curing oven or hot box in my house if I was just a hobby user. M wife would kill me. I think there are some credible alternatives these days though thankfully.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by wizard View Post
    Hi Roc;

    This statement: "With all the hybrid laminates ,the different weaves and the different modulus of carbon and the newer cross linked low temp set epoxies , there is no need to go with the extremely expensive components ." is perhaps the thing that inspires the most questions in your post. For those of use not familiar at all with these techniques we have no idea where to get thee new materials, For example "newer cross linked low temp set epoxies". The "newer" is a big question as I know where to get epoxies for wood working such as System 3 but I have no idea if that is the type of epoxy you are talking about.

    Basically many of the industry sites online are confusing as they either over simply or just leave out details. Hoping for some informed pointers here to advance my research into these processes.

    My advice for any hobby users is:

    Buy your resin from Soller composites. Choose their Adtech 820 and a hardener that is suitable for the size of the part. If it's tiny, their fast hardener is fine. If it's huge and you need more time for the lay-up, their medium or slow hardener is better. I know of no better epoxy laminating resin for small businesses or hobby level users looking for professional results.

    Don't worry too much about the choice of cf fabric.

    Medium and high modulus carbon fiber fabrics and hybrid carbon Kevlar fabrics are nothing new. They are commonly available from most composites stores. Personally, I wouldn't worry about that for this purpose. High modulus cf has increased stiffness to weight ratios at the expense of being more brittle.

    I use some high modulus layers in my cf rifle stocks where high stiffness with minimal weight is important. As many have pointed out here, the goal is not to achieve the minimum possible weight for CNC parts. In other words, you can achieve the desired stiffness using more layers of standard modulus fabrics and.... more importantly.... using a smart part design.

    Most high mod fabrics that are easily available are unidirectional. Anyone that wants some can find it easily enough with a google search. Rockwest composites is one example of a store that sells it. Be aware though, some of there are harder to use for beginners.

    Regardless of what fabrics are chosen, make sure you understand the direction of the weave. The seller should be able to explain this. Fabrics are designed to be strong in one, two, three and occasionally four directions. Find out which directions it is for your fabric and plan your lay up in a way that makes parts strong and stiff in the required directions.

    - - - Updated - - -

    Quote Originally Posted by wizard View Post
    Hi Roc;

    This statement: "With all the hybrid laminates ,the different weaves and the different modulus of carbon and the newer cross linked low temp set epoxies , there is no need to go with the extremely expensive components ." is perhaps the thing that inspires the most questions in your post. For those of use not familiar at all with these techniques we have no idea where to get thee new materials, For example "newer cross linked low temp set epoxies". The "newer" is a big question as I know where to get epoxies for wood working such as System 3 but I have no idea if that is the type of epoxy you are talking about.

    Basically many of the industry sites online are confusing as they either over simply or just leave out details. Hoping for some informed pointers here to advance my research into these processes.

    My advice for any hobby users is:

    Buy your resin from Soller composites. Choose their Adtech 820 and a hardener that is suitable for the size of the part. If it's tiny, their fast hardener is fine. If it's huge and you need more time for the lay-up, their medium or slow hardener is better. I know of no better epoxy laminating resin for small businesses or hobby level users looking for professional results.

    Don't worry too much about the choice of cf fabric.

    Medium and high modulus carbon fiber fabrics and hybrid carbon Kevlar fabrics are nothing new. They are commonly available from most composites stores. Personally, I wouldn't worry about that for this purpose. High modulus cf has increased stiffness to weight ratios at the expense of being more brittle.

    I use some high modulus layers in my cf rifle stocks where high stiffness with minimal weight is important. As many have pointed out here, the goal is not to achieve the minimum possible weight for CNC parts. In other words, you can achieve the desired stiffness using more layers of standard modulus fabrics and.... more importantly.... using a smart part design.

    Most high mod fabrics that are easily available are unidirectional. Anyone that wants some can find it easily enough with a google search. Rockwest composites is one example of a store that sells it. Be aware though, some of there are harder to use for beginners.

    Regardless of what fabrics are chosen, make sure you understand the direction of the weave. The seller should be able to explain this. Fabrics are designed to be strong in one, two, three and occasionally four directions. Find out which directions it is for your fabric and plan your lay up in a way that makes parts strong and stiff in the required directions.



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    Default Re: My carbon fiber CNC gantry

    I totally agree with what Goemon says on every level , don't overthink the components , get what is available and in your price range and go from there . With a clever design that perhaps uses fasteners to tie the two halves together, it is possible to assemble and try it , if it has to much sag ,vibration or flex , you can pull,it apart and add extra layers of laminate . S-glass fiberglass is sometimes as stiff as carbon in certain applications at a cheaper price , so you can probably use this to add layers or you can bond in full length tubes like Goemon did .
    There are many ways to skin this animal and it's up to the builder what the parameters are that are acceptable and what his or her comfort level is working with the materials .



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    Default Re: My carbon fiber CNC gantry

    Thanks

    For people like me that don't have the background simple advice like this goes a very long ways. One of the reasons I prefer steel is that I know all the local vendors and the not so local vendors and generally have a good idea what to specify. When it comes to composites I might as well be shopping in the feminine hygiene aisle, I just have no idea what is what.


    Quote Originally Posted by Goemon View Post
    My advice for any hobby users is:

    Buy your resin from Soller composites. Choose their Adtech 820 and a hardener that is suitable for the size of the part. If it's tiny, their fast hardener is fine. If it's huge and you need more time for the lay-up, their medium or slow hardener is better. I know of no better epoxy laminating resin for small businesses or hobby level users looking for professional results.

    Don't worry too much about the choice of cf fabric.

    Medium and high modulus carbon fiber fabrics and hybrid carbon Kevlar fabrics are nothing new. They are commonly available from most composites stores. Personally, I wouldn't worry about that for this purpose. High modulus cf has increased stiffness to weight ratios at the expense of being more brittle.

    I use some high modulus layers in my cf rifle stocks where high stiffness with minimal weight is important. As many have pointed out here, the goal is not to achieve the minimum possible weight for CNC parts. In other words, you can achieve the desired stiffness using more layers of standard modulus fabrics and.... more importantly.... using a smart part design.

    Most high mod fabrics that are easily available are unidirectional. Anyone that wants some can find it easily enough with a google search. Rockwest composites is one example of a store that sells it. Be aware though, some of there are harder to use for beginners.

    Regardless of what fabrics are chosen, make sure you understand the direction of the weave. The seller should be able to explain this. Fabrics are designed to be strong in one, two, three and occasionally four directions. Find out which directions it is for your fabric and plan your lay up in a way that makes parts strong and stiff in the required directions.




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    Default Re: My carbon fiber CNC gantry

    For me there is much to learn about how such materials would be useful for machine tools. I've been working with metals since I was old enough to enter my fathers garage so there is a lot of knowledge with respect to metals that came from a long time and a bit of the school of hard knocks. I'm too old to spend time learning that way so anything I can pick up from you guys is very valuable. So thanks for the comments.


    Quote Originally Posted by rocrat View Post
    I totally agree with what Goemon says on every level , don't overthink the components , get what is available and in your price range and go from there . With a clever design that perhaps uses fasteners to tie the two halves together, it is possible to assemble and try it , if it has to much sag ,vibration or flex , you can pull,it apart and add extra layers of laminate . S-glass fiberglass is sometimes as stiff as carbon in certain applications at a cheaper price , so you can probably use this to add layers or you can bond in full length tubes like Goemon did .
    There are many ways to skin this animal and it's up to the builder what the parameters are that are acceptable and what his or her comfort level is working with the materials .




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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by wizard View Post
    Thanks

    For people like me that don't have the background simple advice like this goes a very long ways. One of the reasons I prefer steel is that I know all the local vendors and the not so local vendors and generally have a good idea what to specify. When it comes to composites I might as well be shopping in the feminine hygiene aisle, I just have no idea what is what.

    I can totally relate on that. I like working with composites because it is what I am most familiar with. All the different grades of steel are very confusing. It's not complicated. It's just that every purchase involves trial and error which adds time, cost and stress.

    Once you try experimenting with composites they can become addictive (just like milling metal). I still love watching this stringy fabric cure into parts that are stronger than aluminum, titanium and steel. There re is always something new to learn.

    My favorite cf material to use is a 4x4 twill. It's definitely not the cheapest but it produces super stiff parts and is very easy to work with. Much easier than the more common and less expensive 2x2 twill fabrics. It has a really special look to it too.

    For something like my CNC build, I am using mostly a mix of 2x2 twill, chopped cf strands and tri-axial fabric. You can buy 2lb of chopped cf strands off eBay for $30 these days.



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