If you love carbon fiber as much as I do, then you’ll enjoy this video which demos how much stronger a carbon fiber drive shaft is than a steel one:
https://m.youtube.com/watch?v=hjErH4_1fks
I like this practical experiment because it doesn’t talk about that strength to weight ratio stuff which isn’t terribly useful in most real world applications. It’s simply: here’s a steel part and here’s the same part made of carbon fiber. Look how much lighter and stronger it is.
Pretty interesting. They didn’t discuss the production method of the carbon drive shaft, looks like 100% carbon toe.
I agree. It looks to be some type of filament winding process. It seems like the most efficient method of creating cylinder-like shapes.
The guy in the clip is from the British TV show Top gear. It used to be a great show (if you like cars) but not the sort of show that would go into any more than superficial detail on the cf production process. They were just explaining why cf is such a big deal in the performance car market.
I am interested in learning more about filament winding. I like the idea of being able to make parts without molds and being able to specify custom weave directions based on where you need the strength to be. It just seems a little too complex and expensive to set up if you aren’t with a large company.
Judging from the appearance of parts from other auto manufacturers, it looks like sheet molding compound is the preferred method for non-round parts outside of the hyper-car makers.
The interesting thing to me about the test results is that they don’t marry up to a lot of the data online about the strength and stiffness of CF compared to other materials.
The charts on Wikipedia show that steel has slightly greater stiffness than CF pound for pound. That test didn’t just show cf to be stronger than steel. It seemed to show far greater stiffness too. The steel bent with 1/3 of the pressure even though the cf part weighed less. This means that either the online data is wrong, or I don’t understand the online data properly…
You have to use a mold with filament winding. Though it’s called a mandrel. There are various types, some are removed others washed out.
As for material properties… there are various types of carbon which greatly effect things like tensile strength or modulus. And then the ply schedule, geometry, and resin type also make massive differences. This is why composites are more black magic than metals. You cant just compare a piece of steel to a similar piece of carbon and expect that to be the final results.
Filament winding is a good process for particular types of shapes and loads. It’s fairly time consuming and requires specialized machinery to be done properly. If you have money or access to a machine it is probably a useful process.
I have a tube that I made using wet layup and silicone pressure molding for the sampe bridge contest some years ago… i don’t remember the exact figures but it weighed in at like 3 lbs or something silly and held 15000lbs of force on a 3 point bending machine with like less than .1" deflection before it failed on the edge but was otherwise completely un damaged. I could post a pic if you were interested. I used unidirectional sleeve and braided tube. Some great materials and exceedingly strong with super long fiber lengths.
I work in the firearms industry, the new craze is carbon wrapped rifle barrels. With the barrels, they turn down or re-profile the steel barrel blank followed by wrapping with 6K carbon tow and high temp epoxy resins. Using a lathe similar to an old threading lathe, you can control the RPM of the lathe and the feed rate and angle of the tow as it is applied. After post cure, they do mill the profile a bit, not sure how that is done and a quality finish is obtained.
Pretty neat process and I can see a lot of benefits.
Very cool and good information. Did you do regular infusion and some off the shelf epoxy or did you use something special?
For the tube, it was actually wet layup. I used a toughened epoxy from PTM&W that had a very long cure time, I think it was something like 8 or 10 hours with a required post cure. But we actually finished up closed the molds and then heated it to like 150 or 180, so that the silicone would expand and compress the laminate. THing came out amazing. Looks like it was autoclaved. That process is amazing for making very strong parts. A little bit of a pain to make the mandrels and all the molds as they have to be pretty strong to resist the expansion of the silicone. A bladder is probably easier in some ways. Both of those methods work great though.
It’s so true about the “black magic” element of carbon fiber strength and stiffness. It’s a hard one to explain to people who are more used to working with metals that have finite specs.
People like to compare the strength of materials using neat little charts with a simple numerical value for each one but it doesn’t work like that.
A part is not automatically stronger and lighter just because it’s made from carbon fiber. A poorly designed cf part can be heavy and weak. A well designed one can be light and 3 times stronger than steel like in that video.
I agree. Just using black aluminum is a waste of the material. Metal is much easier to predict and machine. The process to get an equivalent or stronger composite part takes a bit more finesse and lots more details. The advantages are worth it if the costs justify. For transportation, it’s a no brainer.
I’d be interested in seeing what your up to? I’m pretty into the 3d printing and composites. THere are tons of possibilities there. I wish I could get my hands on one of the LSAM large 3d printers, and then just print high temp molds… would make things much faster and more interesting.
I went to Thermwood last November and got to see LSAM in action, along with some moulds they made to demo their machine. It was amazing. In discussion with them and Ingersol a bit for their machines. A lot of potential, and a lot of advancements still to be had. SAMPE had a great convention in Seattle a couple months ago, completely on additive manufacturing, small and large.
From what I’ve read seems pretty awesome. The rep was telling me that they have been printing tooling for use in autoclave… vacuum integrity is good and the only issue I think that could be an issue is the CTE of the materials used. They are using high carbon fill plastics for the higher temp tools and seems to be working pretty nicely. He gave me some pricing info for the 10x20x5’… for 1.75mil, it’s not a bad deal. If I could just convince my company to buy one? Maybe once we get to making more tooling? Surely it would cover it’s own cost pretty quickly.
One of the things I am doing right is building a CNC machine to make the molds for my carbon fiber parts. I looked at 3D printing as a potential option first but it wasn’t a good fit for my needs.
None of the affordable 3D printers currently available are capable of producing molds in the required size or quality. Any device capable of printing 30" (or longer) molds with a quality finish is a serious investment.
I decided to go with a CNC router instead as it is possible to build a machine capable of the right size and quality without going over my budget. It also will allow me to make molds in a broader range of materials including aluminum and graphite when I need high temp resistance and the ability to survive repeated use under high pressure etc.
BTW, for anyone interested in this topic, I recommend checking out Compotech’s website.
Compotech makes carbon fiber machine parts such as CNC gantry beams and other cf parts using their filament winding capability. They have a section on the design considerations and what sort of results they are able to achieve compared to steel. It’s a semi interesting resource. I like what they are doing.
It’s one of the places I direct people on other forums when they try telling me that carbon fiber is too light
Or too weak for a specific purpose. The key point is that Compotech gives their customers the option of their CF parts either weighing the same (as the steel they replace) but with extra strength, or being lighter for the same strength.
To me, that’s the right message for carbon fiber design. You can make it as strong, stiff or heavy as you need by using enough layers, orienting the weave in the right directions and designing shapes that are optimal for the material.
That is indeed the right message… also things like corrosion resistance, more stable CTE, vibration resistance, no fatigue, and various others… 
I"m surprised that someone would say it’s “too light”… I guess coming from aerospace, that phrases is basically not in our vocabulary 
those gantry beams look nice… 44% reduction in weight could only be a good thing on a cnc machine. thanks for the link
You get a lot of people on the CNC forums who like to make absolute statements about things they know very little about. When I mentioned that I was making my CNC gantry out of carbon fiber, a number of people who have never tried using a cf gantry, came out with all the reasons why it could never work…
I had to resort to outrageous tactics like using facts, logic and common sense to set their fears at ease. It helped to be able to show that at least two companies were already making and selling successful CNC gantry beams and other parts. It makes it hard to call it “impossible” when it’s in front of them.
The advice from those helpful “experts” included: cf is too light as CNC machines need as much weight as possible to be stable, stiff and to dampen vibrations. Cf parts will delaminate and fall to pieces under the machine vibration, cf is not strong enough for loads and other similarly baseless nonsense.
To be fair, a far greater number reacted positively with more excitement and intrigue than concern.
Most people know carbon fiber as this uber expensive strong exotic material. Any ready made beams or tubes of an appropriate size are prohibitively expensive to them. The information I wanted to share was that cf is a lot less cost prohibitive when you design and make your own parts. It’s hard to get people to even consider using cf when a simple ready made rectangle beam cost $3000…
When you can make a part yourself for less than $100, it’s potential starts to become apparent.
hahaha… yah you gotta love an armchair expert who’s probably never even touched carbon before.
Funny how people are so opposed to the idea of a carbon gantry, when in reality it makes too much sense. Basically it’s advantageous for all of the reasons people were complaining about. Just think about all those jet airplanes vibrating and humming along that no one complains about… I always find it funny when I tell people that they fly on a plane made out of fabric and are none the wiser about it.
and yes, Its’ expensive if you don’t have access to it… sadly I wish I had more time because I have trash cans full of carbon pre preg that just goes into waste… I could make lots with all the carbon scrap i accumulate. It’s really the time and tooling that is the hard part for me. I’m slowly reclaiming my life from the baby… hopefully i’ll get more motivated soon to do some more stuff. Still I guess I work with it so I probably don’t need to go home and do the same! lol
Though I was thinking that making up a CF 3d printer would be pretty cool… just for fun i guess. How big of a machine are you building?
The CNC machine I am building has approx 36" x 20" x 8" of travel. It’s really a small benchtop machine in the CNC world. It’s to make rifle stock molds mainly, so I really only need 30" x 6" x 1.5" of cutting capability.
As I want to make aluminum molds, I figured it would be easier and cheaper to make a smaller machine stable and rigid enough to produce quality results.
I can empathize about trying to get back into making stuff after having a baby in the house. My son is nearly 18 months old and he still keeps me awake most nights. I feel like I could fall asleep standing up some days.
Laying carbon fiber in a mold is the last thing I feel like doing when I am tired. That’s when I make stupid mistakes and end up wasting a fortune in lost materials.
I also find that making the tooling is the most time consuming and expensive part with carbon fiber. I can understand why the idea of making a rigid mold is so daunting for people.
sounds like you’re on the right track. I was thinking about building a cnc router but I don’t have the space. I do have one at work and I’ve used it to make some molds from epoxy tooling board. Aluminum molds are much better for sure. We use a lot of aluminum molds for smaller parts and they are very easy to work with and if you polish out the aluminum, you get a nice shiny part right out of the mold. Just gotta be careful not to scratch them with any tools or while demolding.
I’ve thought about making rifle stocks, seems like it could be fun and a pretty easy thing to market.
So did you go with a design you found or is it your own design? There are so many good parts available now for cnc setups.
little hopes on the high end, but ive seen some wheels wrapped in CF and it actually looks good. despite it being wrapped and not “real carbon fiber” status i was wondering if theres any guys on here who got there wheels wrapped in cf locally? im planning on doing them on my next set of Volks.
A little of both on the design front. I am following some basic build principles that make sense to me. For example, I am mounting the linear rails high for the long axis to get a good amount of gantry clearance for the Z axis travel without needing extra tall gantry risers. This seems to create a more stable machine. Not my idea but I am borrowing it.
My gantry design is my own as I am making it out of carbon fiber and there isn’t much to copy from other people on that.
I have decided to go with an epoxy granite machine base which definitely isn’t my idea. From what I read, this design creates the most amount of stability with the least amount of vibration and lower build costs that the other options.
My CNC machine will have a relatively small footprint as I also have space limitations. It’s one of the reasons why I decided on a thin working envelope as it fits my needs without making an overly cumbersome and intrusive footprint. It should pack away inside a walk-in closet if separated into two parts (gantry and machine base).
It’s definitely a learning process.
Aluminum molds and plugs have a huge advantage (to me) in ease of demolding. Epoxy just doesn’t bond well to aluminum unless you specifically prep the aluminum a certain way.
As for being carful not to damage the mold surface when demolding parts, that applies to all mold materials.
I used to make this rookie mistake every time a part got stuck. I would jam a sharp metal tool down the gap between the part and the mold surface and try to crowbar it out. Almost invariably I would end up damaging the mold surface, the part or even snapping the mold clean in two. It was very frustrating.
Now, I add an extra section at the end of the mold cavity and lay the cf against som plasticine. When cured, I scrape the plasticine away easily leaving a gap large enough to run hot water or air into. The parts then come out without any mold damage.
Some complex part shapes still give me issues sometimes though.
Making cf rifle stocks is fun but incredibly frustrating. I find it significantly more difficult than anything else I make. Choosing the right pattern to start with is key.