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John Hansen
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Does anyone have hands on experience doing resin infusion of carbon fiber with a balsa end grain core. In my research on the methods, I find statements of vendors that indicate balsa end grain can be fabricated as a core between carbon fiber this way but at this time, actual evidence or instructions by someone experienced doing this still eludes me. Does anyone know anyone what has done it (successfully), or is it mere hyperbole by the vendors of the balsa core material? FYI, I have written to one notable vendor with no response. I have also done a patent search and with one notable exception there are no patents that shed light on the process of sealing the end grain. The referenced patent simply says "seal the end grain". But how to seal it and with what to seal it? And how much weight is added to the balsa when it is sealed? Is this all a secret? Looking for replies with experience.... no theories or conjecture, please.
A Lifelong Learner
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Lester Populaire
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+xDoes anyone have hands on experience doing resin infusion of carbon fiber with a balsa end grain core. In my research on the methods, I find statements of vendors that indicate balsa end grain can be fabricated as a core between carbon fiber this way but at this time, actual evidence or instructions by someone experienced doing this still eludes me. Does anyone know anyone what has done it (successfully), or is it mere hyperbole by the vendors of the balsa core material? FYI, I have written to one notable vendor with no response. I have also done a patent search and with one notable exception there are no patents that shed light on the process of sealing the end grain. The referenced patent simply says "seal the end grain". But how to seal it and with what to seal it? And how much weight is added to the balsa when it is sealed? Is this all a secret? Looking for replies with experience.... no theories or conjecture, please. Done it plenty times on kiteboards, furniture and other projects. works very well, but even after sealing it will soak up a lot of resin. The mechanical properties are extremely high tho. this is why balsa cores are used in wind mill blades in the areas of the highest stresses and on composite bridges. For resin uptake you have to do your own tests really. the density of balsa has a huge range and the coating can or cannot make a big difference. i would recommend to use a viscous coating resin or a gel-coat with a short pot life, mixed with microballoons. cheers
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Matthieu Libeert
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+x+xDoes anyone have hands on experience doing resin infusion of carbon fiber with a balsa end grain core. In my research on the methods, I find statements of vendors that indicate balsa end grain can be fabricated as a core between carbon fiber this way but at this time, actual evidence or instructions by someone experienced doing this still eludes me. Does anyone know anyone what has done it (successfully), or is it mere hyperbole by the vendors of the balsa core material? FYI, I have written to one notable vendor with no response. I have also done a patent search and with one notable exception there are no patents that shed light on the process of sealing the end grain. The referenced patent simply says "seal the end grain". But how to seal it and with what to seal it? And how much weight is added to the balsa when it is sealed? Is this all a secret? Looking for replies with experience.... no theories or conjecture, please. Done it plenty times on kiteboards, furniture and other projects. works very well, but even after sealing it will soak up a lot of resin. The mechanical properties are extremely high tho. this is why balsa cores are used in wind mill blades in the areas of the highest stresses and on composite bridges. For resin uptake you have to do your own tests really. the density of balsa has a huge range and the coating can or cannot make a big difference. i would recommend to use a viscous coating resin or a gel-coat with a short pot life, mixed with microballoons. cheers Easy composites has a video of it using wood strips in their longboard video with flax if I'm correct  If you want to be sure, make a small 25cm x 25cm test plate and you'll be able to calculate how strong your laminate is as well as how much the Balsa is soaking the resin
Founder MAT2 Composites X Sports
website: www.mat2composites.com  
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John Hansen
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+x+x+xDoes anyone have hands on experience doing resin infusion of carbon fiber with a balsa end grain core. In my research on the methods, I find statements of vendors that indicate balsa end grain can be fabricated as a core between carbon fiber this way but at this time, actual evidence or instructions by someone experienced doing this still eludes me. Does anyone know anyone what has done it (successfully), or is it mere hyperbole by the vendors of the balsa core material? FYI, I have written to one notable vendor with no response. I have also done a patent search and with one notable exception there are no patents that shed light on the process of sealing the end grain. The referenced patent simply says "seal the end grain". But how to seal it and with what to seal it? And how much weight is added to the balsa when it is sealed? Is this all a secret? Looking for replies with experience.... no theories or conjecture, please. Done it plenty times on kiteboards, furniture and other projects. works very well, but even after sealing it will soak up a lot of resin. The mechanical properties are extremely high tho. this is why balsa cores are used in wind mill blades in the areas of the highest stresses and on composite bridges. For resin uptake you have to do your own tests really. the density of balsa has a huge range and the coating can or cannot make a big difference. i would recommend to use a viscous coating resin or a gel-coat with a short pot life, mixed with microballoons. cheers Easy composites has a video of it using wood strips in their longboard video with flax if I'm correct If you want to be sure, make a small 25cm x 25cm test plate and you'll be able to calculate how strong your laminate is as well as how much the Balsa is soaking the resin Matthieu, Thank you for your input. I have viewed the video tutorial that you mention and it really is an interesting process. My search is for videos that use end grain balsa between carbon fiber with the single objective of lowest possible weight for my UAV frame and monocoque. Many tutorials including the Easy Composite video do not discus how to optimize for lowest weight while achieving the strength needed for the design parameters of the UAV. I am planning the testing you describe and will be creating videos along the way as a way to document for myself my research. I did not set out thinking I would be a pioneer as I do the research in this type of resin infusion. I won't mind receiving the glory and fame of such an endeavor, but I simply did not expect it. :-)
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oekmont
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If you are searching for the lightest possible solution, balsa wood is not what you are looking for. The problem with balsa is that it is highly inconsistent in it's propertys. If you want the very lightest sandwich for medium loads, rohacell would be the optimum. Wet laid in two steps with a skin made of very (40g/sqm) light spread tow or biax. That's what high end uva specialist use for wings etc. This isn't the perfect forum for that light setups. People in forums for model planes are the ones with the most experience for ultra light composites.
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John Hansen
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+xIf you are searching for the lightest possible solution, balsa wood is not what you are looking for. The problem with balsa is that it is highly inconsistent in it's properties. If you want the very lightest sandwich for medium loads, rohacell would be the optimum. Wet laid in two steps with a skin made of very (40g/sqm) light spread tow or biax. That's what high end uva specialist use for wings etc. This isn't the perfect forum for that light setups. People in forums for model planes are the ones with the most experience for ultra light composites. @oekmont,Thank you. There are many lines of research I am pursuing. And I will be looking at rohacell along with others to see if they are strong enough. But my curiosity regarding end grain balsa is as yet unsated. and I have actually looked at a fair number of other forums and thought I would surely find one among the RC aviation groups. But as you say, they are focusing on wings with most of the strength running along the spar. And I anticipate my needs are for a higher strength requirement than would be achieved with 40g/sqm spread tow. My belief is that an ideal strength for my needs would be achieved with 100g/sqm on both side of the balsa and it will need to be the same strength in all directions based on the design. Also, among the RC airplane groups I have not been able to find any forum topics that relate to end grain balsa. Regarding the consistency of balsa, I have found that Baltek offers a variety of densities. Either they grade the wood before processing, or they have some other way to control the density of the various end grain balsa products they offer. And a wet lay that you describe is my second choice. I do not trust that I will get consistent results from a wet layup. That too needs to be confirmed.
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oekmont
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I think the main reasons why balsa isn't that popular are the heavier weight compared to foams, the inconsistency, the soaking propertys and the lack of easy forming methods. Most foams can be brought in shape with a heat gun. With balsa you will have to sand or cut it into shape, if the part is curved in two directions. Wich is the case for most parts you can think of. And the core has very little influence on the strength of the part. A balsa core sandwich will be just as strong as one with an airex core, but the foam core will be significantly lighter. And balsa isn't even that strong. The strength numbers are often taken from heavier pieces. The lighter types of balsa can easily be scratched with finger nails. Easier than airex. Wich is also immune to humidity, has better fire resistance and has isotropic characteristics btw.
You can definitely make nice things with balsa, but in my opinion it is a problematic core material compared to foam, and doesn't have the same performance potential. I only use it for plain, thick sheets or simple beams if price is the main concern. And I work quite a lot with core materials.
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Matthieu Libeert
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+xI think the main reasons why balsa isn't that popular are the heavier weight compared to foams, the inconsistency, the soaking propertys and the lack of easy forming methods. Most foams can be brought in shape with a heat gun. With balsa you will have to sand or cut it into shape, if the part is curved in two directions. Wich is the case for most parts you can think of. And the core has very little influence on the strength of the part. A balsa core sandwich will be just as strong as one with an airex core, but the foam core will be significantly lighter. And balsa isn't even that strong. The strength numbers are often taken from heavier pieces. The lighter types of balsa can easily be scratched with finger nails. Easier than airex. Wich is also immune to humidity, has better fire resistance and has isotropic characteristics btw. You can definitely make nice things with balsa, but in my opinion it is a problematic core material compared to foam, and doesn't have the same performance potential. I only use it for plain, thick sheets or simple beams if price is the main concern. And I work quite a lot with core materials. I'm following Eokmont on this
Founder MAT2 Composites X Sports
website: www.mat2composites.com
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John Hansen
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+xI think the main reasons why balsa isn't that popular are the heavier weight compared to foams, the inconsistency, the soaking propertys and the lack of easy forming methods. Most foams can be brought in shape with a heat gun. With balsa you will have to sand or cut it into shape, if the part is curved in two directions. Wich is the case for most parts you can think of. And the core has very little influence on the strength of the part. A balsa core sandwich will be just as strong as one with an airex core, but the foam core will be significantly lighter. And balsa isn't even that strong. The strength numbers are often taken from heavier pieces. The lighter types of balsa can easily be scratched with finger nails. Easier than airex. Wich is also immune to humidity, has better fire resistance and has isotropic characteristics btw. You can definitely make nice things with balsa, but in my opinion it is a problematic core material compared to foam, and doesn't have the same performance potential. I only use it for plain, thick sheets or simple beams if price is the main concern. And I work quite a lot with core materials. Oekmont, Let's talk about soaking properties. I simply cannot find data that tells me how much it soaks up and how to seal it to prevent the soaking. I have read descriptions of how to deal with it by sealing the end grain, but I am looking for some test data that will guide me in my efforts to seal it. One vendor told me what product to use for sealing it, but they have no data on how much weight is added by the sealing process. My needs do no require forming. nearly every part will be about 6mm thick and flat. Some parts will have a bullnose edge which is easy to produce with a router. If I have to test the strength and compare it to a foam core, I will do it, but I would enjoy knowing how to make the parts with the end grain balsa. End grain balsa is sold for this purpose and is advertised as being suitable for resin infusion. So why am I having so much trouble finding data or tutorials on how to do it. I cannot find any data that compared balsa core with a given thickness to foam core with the same thickness and carbon fiber skins in order to compare apples to apples. I would love to see the data that you refer to when you say that the core has very little impact on the strength. I have looked for it. And if the foam core does exhibit the strength that I need then I will use it, but I would enjoy seeing the data. Balsa is being use so there must be some merit to it. My understanding is the strength of balsa end grain is greater than the foam core. I guess I will have to do the testing myself, but I will still look for data.
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oekmont
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That's the core of the problem. You will not find much data for the resin uptake, because it varies more than 100%. No two pieces are the same. I have had balsa, wich was almost like birch, and I had balsa, wich was like xps foam. I have seen balsa wood with fine structure, and wood with a sponge like structure.
The small influence of the core to the bending characteristics results directly out of the principles of mechanics. And the pressure resistance of a sandwich is proportional to the pressure resistance of the pure core material. It's as easy as that. Have you ever had airex or rohacell in your hands? Maybe you picturing it like insulation eps. Real core foams are incredibly solid. You can drive your car across an airex board without damaging it.
I am not saying you should not use balsa. I am just saying that it seems to me that you are glorifying for some reason. And your image of it being an top end ultralight option ("as light as possible") and much stronger than foams doesn't correspond with my experience.
And resin uptake is a tricky beast itself. other than the used wood, it depends on your resin, the thickness, the surface preparation, infusion aiding preparation and many more.
If you want to seal it, use a quick setting epoxy, or a 2k laquer.
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