# Making of a carbon fiber composite fatbike frame



## Daniel Thomas (Aug 1, 2015)

As the thread title says I am working on a carbon fiber composite frame. I have never built a frame before, so I have spent a lot of time reading, planing, trying to figure out bike specific parts, measurements etc.. I asked a few questions here on this forum about the things I didn't understand. I am confident that I have thoroughly thought this through and I have begun the work. The general idea is to make tubes by bladder molding and then to glue them together using unidirectional carbon fiber wrapping. This is not very elegant compared to more refined more-or-less monocoque techniques, but I believe it is challening enough to start with.

I made a CAD model of the frame and printed the outline on paper. The paper is glued on an MDF board to shape a model of each tube. Here is a picture of the model of top tube. I coated it with three layers of a gelcoat (clear, dark and light gray) and sanded and polished it. I used three colors so that I can see when I get close to sanding through the coating. Sanding and polishing isn't really my strong suit. Let's hope I get better with practice.









I got a scrap piece of chipboard to support the first half of the female mold. The outline of the tube is cut out to allow the model to fit in. The gaps are filled using plasticine. Additionally, small pyramids of plasticine are used to as alignment help for the mold halves. I got this idea from a vacuum infusion tutorial on YouTube. I took those pictures in the middle of the work. The plasticine has to be cleaned up before proceeding.
















I made both female mold halves using a black gelcoat layer and several layers of glass fiber mat on top. This is the first half. Unfortunately I have some irregularities in the surface because of trapped air.









I decided to fill the irregularities with a polyester filler after applying the release wax. It's not pretty, but I thought it might help in avoiding further air inclusions. I have successfully split the mold halves and removed the tube model. There is a defect in one spot, where I probably missed another air bubble, but otherwise the molds turned out alright I guess. I took a picture after washing off the PVA release agent. It was still partially wet, hence the blotchy appearance.









I will make the preparations for the bladder molding next.

Daniel


----------



## Drew Diller (Jan 4, 2010)

If you had a bubble free result on your first try, you'd be a liar.

Everyone makes bubbles their first try. First ten tries.

You going to carve a neck from your existing mold in order to fit a bladder neck?

What bladder material are you planning on trying?

You mention an infusion tutorial - are you planning on doing pressurized infusion, or wet fiber layup and pressurized epoxy ejection?

I want you to know that you started a CFRP related thread WITH PICTURES - this is unusual and appreciated, you are ahead of the game, bud.


----------



## Daniel Thomas (Aug 1, 2015)

Thanks, Drew! The plan is to make a cutout in the mold halves where I left the plasticin blobs at each end of the tube. The larger one will be for insertion of the bladder and the smaller one to get the air out.
I still need to figure out how to apply the gelcoat. I have a UP gelcoat, which needs to be cured before the epoxy comes into play. This means I will have to apply it in the closed mold somehow, because there would be a seam if I were to let it cure in the separate halves. Maybe spinning will work.

I will try a wet layup with a room-temperature curing epoxy. In case I don't get good results this way, I can try to combine bladder molding and vacuum infusion. I have seen tubes that were made this way, so I know it can be done.

I am considering two bladder materials. PE film (e.g. garbage bag) because it does not stick to epoxy and EVA because I can get thicker film that can take a lot of stretch. I will have to make the bladder shape close to mold shape because of the near rectangular cross-section, so stretchability is probably not very important.

Daniel


----------



## Drew Diller (Jan 4, 2010)

I'm afraid I don't have much advice for you on gelcoats, beyond the notion they are heavily recommended to me by others more experienced with cosmetics than I.

I think the theory behind gelcoat is that it is the one place where epoxy travels the least willingly under pressure (against the hard clamp), yet conveniently is easily coated.

It's like when people keep on cutting off a sharp corner of singletrack, and the local dirt boss throws up his hands and builds a feature out of it instead.

One thing needs to be said: seamless molding is HARD. You have to get the fiber bundle into the mold while still allowing the bundle to unfurl on command when pressurized. It can be maddeningly awkward. One veteran put it to me as "trying to wrestle a pissed off baby octopus".

That's a good idea regarding EVA. I'll have to check that out. I often use platinum silicone because of its unwillingness to stick to anything. Epoxy just flakes off it. Fair warning, silicone also has high toughness blends, but they tend to run: start a small tear, and the tear will continue. I've blown up so freaking many bladders, please please please do a dry fiber pretend run first. Hearing a "pop" and then having to wait half a day for the mess to cure is a total b!tch.


----------



## Daniel Thomas (Aug 1, 2015)

The gelcoat has to be brushed inside the mold and cured. I will try to apply it right up to the edge. Maybe some spinning can make the coat merge. If a small seam in the gelcoat remains I will just have to do some additional finishing work with additional gelcoat after the demolding. According to the tech support of the manufacturer that is the standard procedure.

Did you use silicones that can be brushed on a male model? I considered this option to get a pre-shaped bladder, but I decided to try other materials first because the silicone is not that cheap and if I don't get a reasonably even thickness it might not inflate nicely. 

I have some test data from a few EVA grades from work. I thought EVA would be a good candidate because it is much more compliant than PE. The downside is that it will stick if no additional measures are taken (I am thinking additional thin plastic wrap). The material I got is an encapsulation material for photovoltaic modules, so it is basically used as a glue.

Before I do any laminating attempts, I will try to make a Finite Element simulation of the frame to get a reasonable estimate for the layup. I have looked at steel tubes. The wall thickness is around 0.5 mm. This is the target stiffness.


----------



## LyNx (Oct 26, 2004)

Man, talk about really taking the bull by the horns, definitely subscribed to see how this turns out.

With regard to the gel coat, I think that if you brush it on the 2 halves and then clamp together and spin like you say it should give an even coat and minimize a seam, but even if you do get a seam then it's just some sanding and maybe filling to be done.


----------



## ru-tang (May 20, 2009)

Great project- very bold

Couple of questions:

Why do you need a gel coat? If you do a wet lay-up, it should create a good surface on the outside of the tube. It will also add weight. I imagine that you will be joining these tubes together and then painting the whole frame?

There's no mention of what you are doing to seal and prep the mold for wet epoxy? Those surfaces have to be sealed, polished, waxed then coated with a mold release agent. 

If you haven't already spent the money- I would look into Entropy Resin. Its seems to work as well as West System, but its vegetable based. The fumes aren't nearly as toxic.

Last crazy idea: I've often thought of trying a similar molding technique (not for bikes) and I always thought of buying plastic tubing so it won't stick then using an old bike tube for inflating. You could cut the tube in half and seal up the ends to the appropriate length. 

Looking forward to more details and pictures!


----------



## Drew Diller (Jan 4, 2010)

Daniel Thomas said:


> Did you use silicones that can be brushed on a male model? I considered this option to get a pre-shaped bladder, but I decided to try other materials first because the silicone is not that cheap and if I don't get a reasonably even thickness it might not inflate nicely.
> 
> Before I do any laminating attempts, I will try to make a Finite Element simulation of the frame to get a reasonable estimate for the layup. I have looked at steel tubes. The wall thickness is around 0.5 mm. This is the target stiffness.


Silicone can be brushed or slushed or dripped, depending on the particular blend's viscosity. They run quite a range. You're exactly right about the absurd expense, and the sensitivity to wall thickness for proper inflation. Any thicker than 4mm and nothing stretches.

Really though, if you're making a straight tube, you might not need a custom bladder. I'm thinking polyethylene flat-roll tubing might suit this first task.

0.5mm carbon wall thickness? Not very many plies there. I hope you plan on extending the lug work out a ways to simulate the butted wall thickness of a steel reference tube. (That is sort of the fun with composites... don't have enough layers? Then add some layers.)

As ru-tang suggests, and for other reasons, I'd steer clear of West epoxies. Far too viscous.


----------



## Daniel Thomas (Aug 1, 2015)

The gelcoat is for UV protection. Additionally it can polished better than epoxy according the manufacturer.
I use wax and PVA as release agents. I am open to suggestion for something better. Maybe I do something wrong, but waxing and PVAing leaves ream patterns and the mold is not as shiny as it should be. Could be that I just need a finer polish. I bought an additional finer one recently, but haven't tried it yet. Note that the polish must be silicone free, if it's not it might interfere with the release agents.

I'm Austrian and I got my stuff from the German company R&G. They sell pretty much everything needed for making composites.

The 0.5 mm is not for carbon, it is the steel reference. I made some preliminary simulations of just the toptube today. I compared UD layups with a 0.5 mm steel tube of the same shape, looking at bending and twisting. 10 UD layers and 2 layers of braiding with 50 volume percent of resing should give a wall thickness of nearly 2mm and a bending stiffness higher than that of the steel tube, but only about half the torsional stiffness. The ratio of bending to torsional stiffness can be changed by having less UD and more braided tube. I need to spend some more time thinking this through. In particular I need to find out what load cases to look at. So far I have only come across an ASTM standard for frame fatigue testing.

I am not concerned about shaping the bladder, I just want a reliable material. For my rectangular top tube cross-section with lightly rounded edges the tricky part is getting even contact between the wet carbon fiber and the mold wall. I am going to make a thinner PU foam core simply by foaming into the mold and cutting it to size. The foam core will be inserted into the bladder, which will then be vacuumed to make it stick to the foam core. Then the layup will be placed on the bladder (I expect I will curse a lot while doing that). The idea behind using the foam core is that it makes it possible to start with the fabric at a reasonably uniform distance to the mold. I am not sure how to explain it better, but think of inflating a circle inside a square. When the circle touches the edges it still has some way to deform before it fills the corners. Hence I want to use the foam core to start inflating a square. It will still want to inflate into a circle, but it will have to deform less to fill the corners. 

Daniel


----------



## shirk (Mar 24, 2004)

Love following these types of builds. Please keep the info coming.


----------



## Drew Diller (Jan 4, 2010)

Daniel you are all kinds of on the ball with respect to shape deformation / wanting to match the end shape as closely as possible with your fiber preform.

Carbon will settle willingly a little bit -- _a little_. Beyond that, it's just like with any cloth, lots of distortion is bad.

I think this thread is popcorn mode for me now. Keep it coming dude!!


----------



## ru-tang (May 20, 2009)

I guess my thinking on the gel coat is that it will be an extra step and extra weight. If you are painting the frame when it is complete, that should function just fine as a UV blocker. I usually just use the same epoxy with colorants added to form a gel coat. Simple and you won't have any compatibility issues between products.

My composites experience is coming from boat building, so the tolerances and procedures are a little different. 

Popcorn is being popped . . . can't wait to see more


----------



## JohnnyMagic (Dec 7, 2014)

*Goals?*

I'll weight in here since it's the only carbon action ATM.

Is your goal to build a frame, or learn to make dies/molds???

Good on you for making the attempt!

As with anything, doing something many times is the best way to get good at it.
Used to say, "when you've done it a 100 times..."
Since I am only on frame #'s 85-86, maybe I still have a ways to go?

Bladder molding combined with a "wet lay-up" is not practiced by any mfg's for anything that I know of??? For good reasons.

Seems like it will take an awefuly long time to build; plugs/molds/bladder, foam insert???
If that is your goal, then go for it.

When I wanted to "build an MTB". I only had so much time and I wanted to see results quick.

Are you able to build your own assembly jig for alignment?

Tons of commercially available tubes are "mandrel wrapped".

You can build very strong, consistent tubes (including tapered/radius)
quickly.

Built the main triangle for my first MTB, (3 tubes) in 6.5 hrs. Including making the mandrels from Maple I had lying around.
The "S" shaped tube was made in 2 pieces with a tenon so both ends could be removed.
Started with the BB shell bolted to the seat post mandrel so it would be square and co-molded with something.


After (I call it "slapping and wrapping") the main tubes.
I added a biaxial carbon sleeve and used "shrink tubing"
That created a production quality finish that was ready for paint.
Using high-temp resin will prevent bubbles when using shrink-tube.

Just a thought that you might want to re-consider the "process", 
if you want quick results.

If/when you get one complete. You will surely learn a lot and move on to another?

Room temp. pre-pregs can be found that do not need to be kept that cool if you are set on bladder molding.

"have a bar, (Kona handplant) that I want to pull a mold from.
I would leave a "parting line/flange big enough to use breather cloth/vacuum, to remove trapped air.

Another trick is to put precisely cut pieces in both halves before closing the mold/bladder. That will keep your entrapped air hidden ;-)

Keep at it, we need more carbon builders to piss off the "steel is real" crowd 

JM


----------



## Drew Diller (Jan 4, 2010)

Eh I don't think I want to piss off any steel folks (I've ridden many of those, they're good), but yeah this place is painfully underrepresented regarding carbon and needs a shot in the arm.

You guys ever see this? Entry level filament winding. Got one in my basement. It still requires some operator skill and knowledge, but it's pretty neat. X-Winder Store

I like to wrap polypropylene mandrels with 200F prepreg, cover it in heat shrink film, cure it... after cure, the cooling back to room temp causes the polypro to downsize significantly (about a mm across a 30mm diameter rod, so it's not for making tubes with precise tolerances because the mandrel varies so much, making final size calculation tricky) and the mandrel can then be pulled out easily.

No one right way to do this stuff, it's great.


----------



## Daniel Thomas (Aug 1, 2015)

Wow, thanks everyone for your input and encouragement!

ru-tang, I'd like to paint the frame only partially. My road bike is a Look 481 SL with the Jalabert signature. You can find some pictures with Google. I really like the transition from white to visible plain weave carbon to red on this frame. I haven't fully decided yet - still a long way to go - but I might go for a similar finish.

Johnny, that bike looks very nice! There is a video from Felt giving an idea of how they do the bladder molding. I think it would be called a wet lay-up since they are using pre-pregs. It's certainly better in terms of fiber volume content than what I will manage. I calculated the weight of the top tube with 10 UD layers and 2 layers of the braided tube. For a fiber volume content between 40% and 50% the weight is between 245g and 290g. The same tube in *0.6*mm steel weighs 395g (how do you guys measure such weight? Ounces?). Taking into account the additional wrapping and glueing to join the parts, the final weight should be about the same. I would have expected a larger weight. Is the average steel tube really this thin?

I have seen a setup for bladder molding with vacuum infusion. The dry fibers are expanded and then the resin is infused by applying vacuum. I think this is a very elegant method and perhaps I'll try it at some point. It should help towards achieving a higher fiber volume content.

I will most likely use a mandrel and wrap it to make the seat tube to make sure I get the inner diameter right. I don't think I'd manage that with bladder molding. I'll do the same procedure for the chainstays and seatstays because I'll have to fit them around the wheels, avoid the crank and the heels and also attach the dropouts. This is probably going to be complicated.

Anyway, this is what I want the front triangle to look like. The orange parts of the jig are aluminium profiles that I already have. The yellow parts are various pieces like cones for fixing the head tube. Should be a simple matter of getting them machined.









There is some waiting time involved in the preparation for the bladder molding, e.g. 24 hours waiting between waxing and applying the PVA and another night for the curing of the gelcoat. It'll be a couple of days before I can make the first bladder molding attempt.

Daniel


----------



## Carmel (Apr 21, 2014)

First off: great project! As an aerospace engineer I find this highly interesting. 
Just wanna give my 2 cents too.

The wet layup on your styrofoam core seems like it's asking for problems. Fiber misalignment, ondulations etc. I think it is mostly done with prepreg fibers, because you don't have to impregnate them first. 
Working with prepregs at home however is of course not really easy not to mention the cost.

I don't know about bicycle tubes specifically but I have been building a model airplane body with a friend using the same process for the mold as you did.
The difference is that the layup is done in each half of the mold and the bladder is inserted before you close them. When you inflate the bladder the two halfs connect.
The advantage is that the fibers are already molded to the contours.
It is crucial to get a good seal, but lots of people use this process to build planes professionally so it should work. I will try to find a video of the process.

Regarding the bladder, we use Qualatex or Sempertex balloons made for professional balloon artists. They have a good size and shouldn't have to stretch too much to fill the whole tube. The question is if they are strong enough to compress 2mm of carbon fiber.
Just make sure they don't pop, like Drew said. Don't ask me how I know 

I'm also curious what kind of fibers you will use and what weights? I'm familiar with the R&G offerings and think some samurai cloth would make a great top layer


----------



## Daniel Thomas (Aug 1, 2015)

I made some first attempts at making a bladder. I tried to make bladders from PE films using a soldering iron as demonstrated in a video I found during my research on bladder molding. I made five bladders until I managed to make one that was airtight. I wasn't happy with the strength of the films I had though. I need to try a film that can take some stretch. I also tried a road bike tube, but it didn't take the required stretch to fill the tapered mold. So I am still looking for a good material. I will look at the ones you mentioned! Perhaps I can also get a suitable latex grade from a polymer chemist I know. Haven't given up yet.

I cannot do the layup in each half because I want to use braided sleeves. I got the 60mm diameter one from R&G, it's 6k. I also have 3k UD tape and plain weave fabric. I looked into load cases for bike frames and what I have seen so far is that the primary loads are torsion and sideways bending. In light of these loads, the plain weave fabric is not that good. I haven't completed the FEA, but I expect that I will be using the sleeves for more than just a nice looking top layer because they are my best option of improving torsional stiffness.

I had no trouble laying the fabric on the foam mandrel, which is why I believe it will be fine to use this for the bladder molding as well. 
I am considering the possibility that I will not be successful in bladder molding the top tube. As an alternative, I made a PU foam mandrel simply by foaming the mold. I put a layer of the fabric on one side and vacuum bagged it. I was curious about the surface quality and it turned out nice. There is a number of small pinholes, but I think it will look nice with a gelcoat or a two-component PU finish. I applied polyester filler to get a sandable surface. I'll post pictures of the mandrel when I am done sanding.

You're right about the samurai cloth. It would definetly make a nice top layer! Maybe I will get some when I have more practice. For now I will stick to cheaper materials.


----------



## Drew Diller (Jan 4, 2010)

I tried the welded polyethlyene sheet with a soldering iron thing as well. I had something like a 15% success rate at making airtight bladders. One of them sorta did the job for a little while, but it quickly became obvious that I didn't have the skill to make bladders that way.

One easy low-expense way of casting a bladder from a mold is to use mask maker's latex, very very thin out of the bucket. Have to rotate it otherwise you'll get thick/thin spots. Downsides are that the resulting balloon will stick to epoxy when left to its own devices, the application is noxious and requires a warm fresh air environment, and many applications are needed to build up wall thickness without drooping.


----------



## Daniel Thomas (Aug 1, 2015)

This is the foam core, roughly sanded with 100 grit sand paper. Nothing special about it.









I am going to use it to test the handling of the UD tape and the braided sleeve. I am hoping to get a nice top tube out of it because it's a fairly expensive material. If it works fine I can buy a larger quantity at a less painful price.


----------



## Daniel Thomas (Aug 1, 2015)

These are braided sleeves and some UD tape prepared for laminating.









I mixed the resin by weight to get a fiber volument content of about 40%. I put the UD tapes on the side to reinforce against sideways bending. The braided yarns are aligned at angle to the tube axis which is good for torsional stiffness. The braided sleeves are like chinese finger traps to work with.
I vacuum bagged it and waited for the epoxy to cure. Overall I am fine with the first attempt. There are some flaws that are not only cosmetic but also structural that I need to avoid in the future.

The cured tube with a resin seam from the vacuum bag









Here is a closer view of the side. There are some small holes between the yarns here and there, which I expect to disappear when I put on a top coat. The braided yarns don't look as nice as a plain weave fabric because of the spacing between the yarns.









There are two structural flaws in the following picture. There is a strip where resin is missing on the surface, no idea why. I don't think it is a big deal. There is one spot where the tube is indented. I suppose there was a void in the foam core that collapsed when I vacuumed. I didn't notice it until today. It is on the bottom of the top tube in the section close to the head tube.









Now I have to decide what to do with it. I could finish it with filler and paint and use it. Or I could do a three-point bending test to test the bending stiffness and strength.


----------



## ru-tang (May 20, 2009)

Check out this heat shrink tubing for this type of application. I use it for reinforcing wood paddle shafts. You can wet out the sleeves, lay it over the mandrel, then slide this stuff over and hit it with a heat gun. Start in the middle and work out towards each end. Then you slice it off when its all cured, leaving a really good surface.

Might save a few steps and doesn't leave the little crease where the bag folds.

http://composites.sollerpaddles.com,carbon-fiber,carbon,fiber,sleeve,fabric


----------



## JohnnyMagic (Dec 7, 2014)

Can vouch for this company.(Solercomposites.com)

Have been using them since 08'. Get all my carbon sleeves, tape, some fabric and shrink tubing.

Mentioned that process above^^^

A few times the fabric was not up to snuff? They exchanged or took care of it right away.

Using the shrink tubing is a process/learned technique.

Have to be careful with tubing dia. (if your shrink tube is too big, you won't get enough compression.

When it is nice and tight, (just bigger than you need)
it's a be-otch to place over a wetted tube.

He has been pushing a new "clear" shrink tube.
DON'T EVEN TRY IT!!!

It has less mil. thickness than the black (tried and true) stuff. 
(won't deliver enough compression by itself.

He even has a new instructional video on the clear stuff. (again, stay away)
In theory it would be nice to "see" while you are applying heat.
Enough heat and it just makes holes.

Like I said above, using a "high-temp" resin prevents air bubbles from the heat.

Still a slick process that I use for custom bars and any other quick tube building.

Drew's mandrel wrapping machine looks like the fa-shizel for orienting fibers at various angles.

I just use "0-90, and 45 degree" cloth.
On that MTB above, the sleeve was the "cosmetic" layer.

You can get "uni-dirctional" and biaxial sleeve if your really worried about it?
Bamboo tubes are working 

You don't have to "over-think" (testing/F E A) ???

Go to a frame supply site, check wall thickness, cross reference for your chosen material
(in our case carbon ;-) shoot for that wall-thickness.

Getting one under your belt will surely be inspiring to build another type/model.

JM


----------



## Daniel Thomas (Aug 1, 2015)

I know it was mentioned above. I will do the seat tube this way to make sure I get the inner diameter right. I already bought a shrink tape for this, but it wouldn't fit the top tube. The top tube also tapers from about 60mm diagonal to 30 mm, which might be a bit much for shrink tape.
I imagine it is tricky to pull the shrink tape over the wet carbon fibers. It was already a slow and careful process to do it with the oversized vacuum bag because it would always stick on at least one side.

Had a pleasant surprise today. I received a sample of two-component silicone. I asked for it weeks ago, didn't think I'd ever get one. The sample is a can of 4.5 kg  . Not sure about the viscosity. Perhaps I can use it for dip coating.

I don't see doing an FEA and trying to consider the loads experienced by the frame as overthinking. For me it is interesting to explore options provided by the composite material. It's something I want to learn more about. I deal with testing and simulation for a living, which gives me a head start in doing it.
I am not going to use 0/90 fabric except maybe as nice looking top layer. The 45 degree cloth you mention... I suppose that would be a biaxial non-crimp fabric. I believe that is a very good choice for straight tubes made using a mandrel, both in terms of the mechanical performance and the price of the material. I should get some for the seat tube. I can't use it for the top tube and down tube because it can't be drapped on tapered or curved tubes.


----------



## JohnnyMagic (Dec 7, 2014)

Twill weave;
most of my builds are "S" or "Z" shape frames.





A twill weave creates a nice chevron, or herringbone. (I build in two halves).

So, long strips are used "tip-to-tail". Continuous fibers running the length of the bike.
45 degree (50" cloth cut at that angle) is run (overlapped) at BB, head-tube, seat junctions, etc.

One of my bikes (and the rack it was mounted to), fell off a car going 65 mph. down the highway. (dumb-arse customer). Reportedly went end-over-end 10-12 times.

When he sent it back for inspection, I thought it would be toast and I would get to build him a new frame? NO structural damage at all.
(it bounced nose to rear wheel) over and over. Nose was gouged a little.

Bicycle loads/dynamics are some of the hardest to simulate. (even for pros).

Tapered/shaped tubes have better resistance to bending/twisting. 
(round tube deflect equally in ALL directions)

Keep at it!
JM


----------



## JohnnyMagic (Dec 7, 2014)

Oh,
the shrink-tube DID conform to the tapered/radius tubes on the MTB.
The shrink rates are listed on his (Solars's) site.

JM


----------



## Daniel Thomas (Aug 1, 2015)

Very nice! Don't put ideas in my head, seriously! The twill weave is looking great! Is that the surface you got from shrink tubing it or is it coated and polished?

I was thinking of wrapping. Building halves with twill weave would probably work because halves only taper in one direction. Have you tried non-crimp fabric for the hidden layers? With NCF you should be able to achieve a higher fiber volume content and ligher but also stiffer structures. And it's cheaper than woven material.

My design considerations were referring to more traditional frames with a front and rear triangle. There are some tests for frame stiffness like the Rinard test or the tests used by the Tour magazin, which are offered as a service by a company called EFBE. These are static tests where load is applied and a deflection is measured. They are not hard to simulate. Simulation actual riding events is a different story. I am content with simulating the simple tests. I have ordered more carbon fiber today (I'm sticking to european suppliers because shipping across the ocean and dealing with customs and import tax is not very attractive, in particular considering the current exchange rates) and I have decided to test the first tube to failure. Right now, the simulations rely on data sheet values for the resin, the fibers and some assumptions to calculate the composite stiffness. I would like to see if I can get the bending stiffness about right.

Thanks again for sharing the pictures! I'd love to ride the second one!


----------



## JohnnyMagic (Dec 7, 2014)

Those bikes were built from production quality molds.

(still have to fill pin-holes and spray with U-V protected top coats)

Not sure what "non-crimp" fabric is?

My ratio is at 33-35% resin to fabric.

Mostly use the twill weave oriented like I said.
Use uni-tape in guitar necks.

The shrink tube will only work on somewhat simple/shorter tubes.
Anything on a diamond frame.

The LWB has been a blast off-road! 
Only set up the road wheels to see what the weight would be
if someone wanted that info.

It was 26 lbs. A typical LWB recumbent weighs closer to 36 lbs.!

JM


----------



## Drew Diller (Jan 4, 2010)

JohnnyMagic said:


> Not sure what "non-crimp" fabric is?


Perhaps he was referring to Textreme?

TeXtreme® Website | TeXtreme.com

Very nice, plenty of $$ needed, would love to try it some time.


----------



## Daniel Thomas (Aug 1, 2015)

Sorry about the confusion. Maybe there is another term for it that is more common. A non-crimp fabric is made of layers of unidirectional fibers at whatever angles are desired and then stitched together. In woven fabrics, the fibers are undulated. Stiffness, strength and density become better the less wavy the fibers. It is also more economic to use if you want 45 degrees. Cutting a 45 degree strip from 0/90 fabric produces a lot of scrap.

TeXtreme is nice stuff. It's called spread tow fabric. The Samurai cloth that was mentioned before in this thread is such a material. Like you said, $$. I'll consider other than cosmetic use in the future, when I have gathered more experience in the processing and design. Now I would just be wasting a good material.


----------



## Drew Diller (Jan 4, 2010)

Daniel Thomas said:


> Now I would just be wasting a good material.


Haha, I feel ya there. I appraise my state of the art similarly. Practice practice practice...

Thanks for the terminology clarification. I've had some confusing moments with this pursuit because of names of things.

Find the right word and suddenly Google becomes _all kinds of helpful_ all of a sudden rather than making me trudge through pages of crap results.


----------



## JohnnyMagic (Dec 7, 2014)

Aha;

it's called uni-directional fabric from my suppliers.
Comes in "tape" of various widths and up to (12"??) wide strips.
At zero and 45 degrees.

My first full-carbon MTB was the Scott Scale. (one of the first few built in Germany with a lifetime warranty). Within a few months production was done in Taiwan with a 1 year (?) warranty.

It had spread tow and looked pretty cool.
Have seen some forks with that top layer also.
It does not drape and conform well to complex shapes. ( mass-production stuff is pre-preg)

Solar sells it sometimes.

JM

JM


----------



## Daniel Thomas (Aug 1, 2015)

Times flies when you are having fun. It also does when you are very busy at work and a drop in temperatures is giving you troubles. Since my last post the temperatures have dropped to around 3°C/37°F in the morning and reach about 15°C/60°F in the early afternoon when it's a sunny day. These temperatures are not very composite-friendly. I spent some time building a crude heat box using XPS insulating wall panels, 400 W of light bulbs and a thermostat. It works nicely. I set the thermostat to 35°C/95°F to make the mold for the down tube. Curing took less than an hour!

I still don't have a good bladder. Owing to the low temperatures, I have given up on bladder molding for now. I'll try that again in spring when the temperatures are nicer. Right now, I find it frustrating, not only because of the adverse temperatures in my garage, but also because winter is approaching and I want a bike to ride when the snow comes.
I wanted to make the head tube and the seat tube by wrapping and vacuum bagging a male form because the inner diameters should be correct to fit the head set and the seat post, respectively. I have changed plans and bought some shrink tubes for this. Since I have vacuum pump at hand, I decided to use it for vacuum infusion instead of vacuum bagging. I made a test piece using a scrap piece of steel tube and it worked fine. I did the test at 6°C/43°F and it still worked, but the resin is noticably more viscous at this temperature. It took a while, must have been at least 20 minutes, to infuse the short piece. I didn't degas the epoxy, so there are some pin holes, but the process works.









I have male models made of polybutylene for the head tube and the bb shell. I don't know the details of this particular grade, but in general it should be a good material for the purpose because epoxy won't stick to it and it has a high coefficient of thermal expansion. The idea is to freeze the cured parts for easier removal of the core, so the higher the thermal expansion coefficient the better. Ready for vacuum infusion:









I have put some UD glass fiber on the inner side to separate the carbon fiber from any metal parts, such as the head set or the pressfit cups. I am not sure if there would be any problems with corrosion on painted or anodized parts, but why take the chance when it is just the simple matter of adding a glass fiber layer. Due to the taper on the head tube, I could not wrap all of it with the UD glass fiber, so I just put it on the cylindrical parts. A sleeve of glass fiber would have been a good idea. On the other hand, this part will be wrapped with UD carbon fiber when joining the frame, so at this stage the look is not important.

I put the layers of carbon fiber sleeve on the bb shell model. The tricky part here is to put them on as taut as possible. I could have used another pair of hands for this. If the sleeves are too slack, the air pressure will cause wrinkels when the vacuum is applied. I did my best but there are some small distortions. This will require some special attention on the curved down tube, because it will not be possible to pull it tight.
But I'm not there yet. I still have some left-over quarter inch steel sheet from a smoker I am building together with a friend. I am going to use pieces of it to weld a box for degasing the epoxy resin. I also need to finish the FEA to decide on the number of layers for each part. I have made a rough sketch of the seat and chain stays to complete the CAD model. I am rookie at CAD and I still struggle with some parts, e.g. for some reason unknown to me, the taper on the top tube no longer works. Well this is what I got so far.


----------



## Carmel (Apr 21, 2014)

I know that real desiccators (Exsikkator in German) are expensive, but I would guess it is difficult to weld a box that can withstand a high vaccuum. This is just an assumption though.


----------



## Daniel Thomas (Aug 1, 2015)

Hmm, good idea. I suppose I could borrow a desiccator from work for a few days.

I infused the two assemblies shown earlier. It's getting better! After curing I put them in the freezer for a couple of hours. I thought I would have whack the polybutylene cores with a hammer to get them out. I was very happy that this wasn't necessary. I only lighty hammered on the one for the bb shell and it immediately gave way. The one for the head tube only required a gentle push with the thumb to pop out. Thumbs up for polyolefines!


----------



## Drew Diller (Jan 4, 2010)

Pretty cool!

Infusion really works, eh? (Mr Bean eyebrows)

It's not too shabby.


----------



## Daniel Thomas (Aug 1, 2015)

Since the last post I have finished the FEA. I built the models using data sheet values and some assumptions because I do not have any test data. I could have prepared some specimens for testing, but in my beginner stage I'm fine with a good estimate. I simulated the Rinard stiffness test for the front triangle and the predicted deflection is about 6 mm. The torsional stiffness according the EFBe track-holding rigidity come out around 100 Nm/°.

Made the down tube again using vacuum infusion and a shrink tube. In the curves there were a few distortions of the fibers in the sleeve. I am not concerned about it because in a braided sleeve the fibers are never straight anyway. Nonetheless I reinforced those areas and put a top layer of 0/90 plain weave fabric on it for the looks. Unfortunately, I missed some shearing of the fabric when I wrapped it around the curved tube. Other than that it worked, I might even try it with more expensive spread tow fabric for a nicer look. One issue I have to look at first is the PVC shrink tube. In some spots it stuck to the down tube. I had to shave some pieces off with a sharp blade. I am not sure about the reason for the sticking. Maybe too much heat.


----------



## mapex101 (Oct 30, 2013)

Quick question about FEA, what software package are you using? Keep up the posts, great work!!

Sent from my SM-N900V using Tapatalk


----------



## Daniel Thomas (Aug 1, 2015)

I'm using ABAQUS.


----------



## Daniel Thomas (Aug 1, 2015)

I have been too busy at work these last two weeks, but I am happy that I still got a few things done and that I can give you an update once more. I have made the top tube and and the seat tube using the shrink tape method. The pieces for the bb sheel and the head tube that I posted earlier were shortened to their desired length by a co-worker on the lathe at work. I have done a preliminary glueing of the parts to make the front triangle. Now that they are fixed in their position I can apply the final wrapping with carbon fiber.









We have also done a bending test on the first trial top tube I made using hand lamination and vacuum bagging. I will show you the results tomorrow! I have taken pictures and a video, but I still need to sort through the pictures and see if I can figure out how to post-process the video because it is just a rough one taken with my cell phone.


----------



## LyNx (Oct 26, 2004)

That's frikin awesome Dude. It may take you a while, but riding something you built with your own hands, time and knowledge will be incredible. I know I'm jealous as heck, wish I had the patience and knowledge to even give something like this a try.



Daniel Thomas said:


> I have been too busy at work these last two weeks, but I am happy that I still got a few things done and that I can give you an update once more. I have made the top tube and and the seat tube using the shrink tape method. The pieces for the bb sheel and the head tube that I posted earlier were shortened to their desired length by a co-worker on the lathe at work. I have done a preliminary glueing of the parts to make the front triangle. Now that they are fixed in their position I can apply the final wrapping with carbon fiber.
> 
> View attachment 1028288
> 
> ...


----------



## Drew Diller (Jan 4, 2010)

Haha, yes! Reference cats are important for 80/20 jigs.

Looking really good, keep it up.


----------



## Daniel Thomas (Aug 1, 2015)

I can't believe it's already been three weeks since my last update. I didn't manage to write the next one before my trip to Houston. The trip itself was great. Besides getting to see a little of the weightlifting championships I also bought a lot of bike stuff including the Turbine Cinch crankset. My new bike shop of choice also finally finished the wheels. It took some time for them to get the Hope hubs. Unfortunately, they didn't find any good orange spoke nipples. I hope I can find a good orange rim tape sometime.









Now that I have all the stuff together, I can continue by fitting the chain stays. This will be tricky, staying clear of the tires, the cranks, the chain, the heel and not getting in the way of the rear derailleur. I already mounted the Turbine cranks, but I am afraid I am doing something wrong. The BB shell is 100mm wide. The carbon fiber tube has an inner diamter of 41mm for Pressfit-to-BSA adapters. The spacers needed according to the Raceface chainline document were included. There were also two smaller rings whose purpose I don't know. So I mounted the whole thing and found that there is still a gap of about 2mm left.









I am probably doing something wrong because I don't fully understand the cartoon that comes with the crank (I won't call this scrap of paper instructions). I guess I will have to find or make another spacer.

http://www.raceface.com/instructions/CRANKS/Cinch_System_Installation-rev1.pdf

I don't know what 80/20 jig means, but I do know that I will do it differently when I am going to start #2 in summer. Contrary to my expectations, this profile systems does not automatically align well. I did my best to set everything up properly, but I believe I won't know if it's good enough until I have both wheels on.

A while back I showed a picture of the first trial top tube I made by vacuum bagging. We have tested it in the lab at work to see how it will do. I would have preferred to do a torsion test, but bending is really the only feasible option for this kind of tube. Here is a picture of the test setup









We tested it slowly to failure. It took a load of roughly 4500N (this is a weight of about 1000 lbs) before there was a fracture in the top wall right under the bending fin. We then proceeded to break it all the way through. The force needed to keep breaking it was fairly constant at about 2500N or about 560 lbs of weight. This video is accelerated because we tested slowly so we could observe what's going on.


----------



## Feldybikes (Feb 17, 2004)

Funny, I just went through this same process with some raceface cranks on a fatbike I'm building. I got the aeffect crank, which also uses a different BB (24mm spindle vs. the 30mm of the spindle), so this might be different for you, or it might help:

The bottom bracket came with one 2.5mm spacer, but it needs 3: 2 on the drive side and 1 on the non-drive side. The fact that you can screw everything together to the point where it looks like you might only need one extra spacer makes this not so obvious, but check out this chart: http://www.raceface.com/comp/pdf/FATBIKE-CRANK-CLEARANCES.pdf



> There were also two smaller rings whose purpose I don't know.


Not 100% sure what you're talking about, but I would guess you're referring to the pedal washers. Those also confused me for a bit before I figured it out.


----------



## Daniel Thomas (Aug 1, 2015)

Pedal washers makes sense, thanks!

There were three spacers included in the BB and the crankset came with the other two mentioned in that PDF. I have all those spacers in place. I measured the Q-factor (distance between the outer sides of the cranks as drawn in the PDF) and it's 212mm. That's 10mm more than the target Q-factor, or an estimated 8mm accounting for the gap. This will require a closer look at the whole assembly.


----------



## Eric Malcolm (Dec 18, 2011)

450kg is way more than needed, any steel/alloy tube would have failed way sooner in a test of that nature. It seems to be a sad waste of a tube to find that out! That's approaching 6 times my body weight. You can take such figures and redo with a lighter construction or be sure it's more than adequate as is.

Eric


----------



## Daniel Thomas (Aug 1, 2015)

As this is the first frame I'll go with more than adequate! I am using mostly 24k braided sleeves. I chose this material because it is significantly cheaper than the ones with less fibers per yarn, such as 6k or 3k. The downside is that there is much less potential for fine tuning. I made a short test piece with just 1 layer of the sleeve and it was not very stiff. 2 Layers on the other hand are already very stiff. Still the heavier fabric was a good choice for me too learn because screw-ups don't hurt the wallet as much. So far all the tubes worked out fine, but I wasn't certain of this in advance. Concerning the making of tubes, I am confident that I can optimize this with more expensive material for the second frame. Speaking of weight optimization, I wasn't very smart with the dropouts. I wanted to weld some tubing on the dropouts which would serve as interface to the carbon fiber seatstays and chainstays. I couldn't find a suitable tube with enough wall thickness, so I used pieces of a M16 thread rod (M16 is a 16 mm metric thread). I only realized how much weight this adds when I held the assembly with the cured carbon fiber parts in my hands. The thread rod adds about 400 grams/14 ounces of weight. So there is a serious instant weight saving potential there.

I have just began working on the final bonding of the frame. I applied a mixture of epoxy and short carbon fibers to hold the parts together for the final wrapping. Here is a picture of the vacuum bagged top tube, seat tube and seatstays.









It is not possible to use a single bag for this. I used to sheets of polyethylene film to get two halves of a bag and some duct tape to seal it. As you can see in the picture, I didn't make it slack enough to get it to fully conform to the frame. I fixed this afterwards by heating the polyethylene with a hair dryer. When warm the plastic becomes much more pliable. The ambient air pressure is then strong enough to stretch the film and make it follow the frame shape.


----------



## Drew Diller (Jan 4, 2010)

Nice tip regarding the heat to address bag bridging. You're better at vac taping than I am that's for sure!


----------



## Daniel Thomas (Aug 1, 2015)

I learned something new about vacuum bagging. It works a lot better with very thin films. The previous yellow one is from a sturdy waste bag. I picked the thicker one because I was concerned the thinner ones might be punctured easily. This is with a thin one. It conformed to the underlying shape really nice and there was no problem holding the vacuum.









Next I used a polyester filler to do some cosmetic work on the now assembled frame.









I really dislike the filling and sanding. I have decided to mount the components before putting more time into it. I want to know if everything works as planned before investing the time into the looks. It took me the major part of the day to work my way through SRAM's hieroglyphics. They are just as bad as those of Race Face. Speaking of it, I bought a 2.5 mm spindle spacer because I couldn't figure out the source of the gap. Everything is mounted and working. I failed to figure out how to adjust the rear derailleur, so I took it to the bike store that made my wheelset and asked them to fix it. I got there 15 minutes before they close, but it was no problem. If it wasn't for the chatting, he would have finished the adjustment in two minutes, commenting that I seem to have tried every screw there is. Can't deny it. So tomorrow is the big day. I will take it to the trail and see how it goes!


----------



## Feldybikes (Feb 17, 2004)

Daniel Thomas said:


> I really dislike the filling and sanding.


So do a lot of other people who chose TIG over brazing. I'm not as smart as those people. I can't imagine all the dust with composites makes it much more fun.



Daniel Thomas said:


> I failed to figure out how to adjust the rear derailleur


I think it's funny that you built a frame from scratch including making your own tubing yet had trouble installing the components. To be clear, I mean no offense here and mention it only because you seem to have a sense of humor about it as well.

Let's see some pictures of the build bike and some acton shots!


----------



## Daniel Thomas (Aug 1, 2015)

That's right, the dust is bad. I did all the sanding outdoor because otherwise it would be everywhere in the garage. There is no real winter yet, so it is no problem to do it outside.

I did a fairly long test ride today. There are a couple of nice singletrails in my area and my favourite one is up the mountain right from my place. It had to be this trail. It's about 800 meters or 2600 feet up to reach the summit. I was riding with one of my biking buddies, but he was a little hung over and only wanted to do a short trail which goes about half way. We did that, but it felt insufficient, so I rode the full trail afterwards. I did about 4000 feet in net elevation, which was pretty tough following a month with little riding due to travelling and catching a virus. Shopping groceries with my wife afterwards was hard. One minute I wanted to take a nap in the cart, the next I wanted to eat everything in sight. But it was totally worth it because this was it looked like outside, about 150 feet above my place









Temperatures were only slightly above freezing. On the mountain temperatures in the sun were probably around 10°C/50°F, which is incredible for this time of the year!









My friend wasn't up for taking a ton of pictures. Unfortunately I don't really have any action shots. This is the only somewhat useful picture he took!









But here are some pictures of the preliminary setup. I still need to make some fixtures for the cables and brake hose. For now I just used zip ties.



























I estimate that there are 7 mm of clearance between the wheel and the seattube.









There is plenty of space between the chainstays and seatstays. The chain also clears the wheel easily.









This is at the top of the mountain, ready for 2600 feet of singletrail. It ends about 1/3 mile from my place. I love it!









The trail has a few sections that require balance and precise steering. I was surprised how smooth I could ride them. I had zero problems there. I was a little behind in the timing in the faster turns, but other than that I didn't have to adjust to the bike at all. There are no drops on this trail, but I rode it as fast as I would with my hardtail. Not as fast as I do with my all-mountain obviously, but I didn't hold back. This is one of the bumpier sections. The bike is still in one piece. I'm happy! I have a wall with varying height in my garden, I can try dropping there and see what happens.









The guy at the bike shop had a hanging scale and he was curious so we checked the weight. It's 15.4 kg/34 lbs, with pedals and everything. I was prepared for worse. I can save 400 grams on the dropouts, but other than that... I wish I knew how much weight I could save without compromising strength.


----------



## JohnnyMagic (Dec 7, 2014)

Congrats!

A little late but;
bagging films can be had in various degrees of "stretch" or elongation.

"Strechalon 2000" is a popular one. I just order the "stretchie blue bagging film.
The Strechalon stuff has WAY more expansion.

Using proper bagging films and double stick tape makes for a nice clean release and you can remove then re-apply as needed.

Fillers;
"Aero-poxy is an ultra-light filler used on high end planes. Spreads very nicely.

If you "tint" (with pigment), it black. It can be left on without having to paint over it.
MUCH lighter than epoxy/micro-balloon mixture. Doesn't shrink, or crack. 

Some "garbage" bags will stick to some epoxies. Can be scraped with a razor blade but VERY time consuming.

JM


----------



## LyNx (Oct 26, 2004)

Looks awesome man, so cool to be able to do something like this for yourself, really must give a big feeling of accomplishment and pride _(once it rides right and doesn't break)_ :thumbsup: What colour are you going to spray it or design? If it were me if the carbon where no filler was used is smooth and good, I'd consider just spraying the areas where the filler was needed and leave the raw carbon elsehwhere.

Glad I'm not the only one who found this funny  I would have no clue where to start on a project like this, but I can pretty much figure out anything to do with a bike :skep:



Feldybikes said:


> I think it's funny that you built a frame from scratch including making your own tubing yet had trouble installing the components. To be clear, I mean no offense here and mention it only because you seem to have a sense of humor about it as well.
> 
> Let's see some pictures of the build bike and some acton shots!


----------



## Daniel Thomas (Aug 1, 2015)

Aero-poxy sounds very good, thanks. It's more than 30% lighter than the polyester filler I am using. I will have to get this for the next one!

Yes, I am thinking about spraying only the sections with the filler in orange color to match the hubs and the rim tape. I will see if I can manage a nice transition from orange to plain carbon. It might be few months before I can try that because it is too cold now. I have no heating in my garage except for a small fan heater. It is enough to warm myself a little when working in the garage but that's it. Maybe if I can get rid of all the dust in the garage I can use additional heaters. I know nothing about painting, still need to read up on it. But I have a compressor and a spray gun already!

I really like the 1x11 setup. With a 26t chainring I have no problem on the local uphills and it is very elegant system, but I admit that avoiding the complication of installing a front derailleur also contributed to the decision to go 1x11. It is bugging me that I didn't figure out how adjusting the rear derailleur works, but not enough to get stuck into it.


----------



## JohnnyMagic (Dec 7, 2014)

Before filler;

After only 12 grams before sanding) of Aero-poxy.

Also before I learned the "tint it black" trick;


Liked the paint scheme fine.

JM


----------



## toddsters (Dec 24, 2015)

Hello Daniel,

I was wondering how you dimensioned your polybutylene mandrels, given the thermal expansion. Did you machine the mandrel at the same temperature as your cure temperature so that the bb and the headtube would be accurate diameters?

I don't know if you looked at this thread for bladder molding. I have not tried it, but it was an interesting thread: Fuse Molding with an Inflation Bladder - RC Groups


----------



## Daniel Thomas (Aug 1, 2015)

Yes, it was done at the pretty much the same temperature, but that's not difficult because I was using a room-temperature curing epoxy.

I tried the method from the video, but I wasn't successful. Perhaps I had the wrong plastic film, or my soldering iron is too hot. Maybe I am just not skilled enough for this method. Who knows. 

Daniel


----------



## Drew Diller (Jan 4, 2010)

Daniel Thomas said:


> Yes, it was done at the pretty much the same temperature, but that's not difficult because I was using a room-temperature curing epoxy.
> 
> I tried the method from the video, but I wasn't successful. Perhaps I had the wrong plastic film, or my soldering iron is too hot. Maybe I am just not skilled enough for this method. Who knows.
> 
> Daniel


I never got the method to work reliably. The failure to viable bladder ratio was just absurd, and the one bladder I did get to work couldn't get even fill like I'd hoped.

It's effective for making RC plane fuselages, basically.

Taking a 3D soluble core as an air chamber and skinning it (or, some other way of making a balloon, lots of ways to do it) with latex or silicone or _your-resin-here_ will create pressure bladders that have a _somewhat less torturous_ life than the very abrasive, unfriendly job they are tasked. The less deformation you ask a pressure balloon to do, the better. The bladders I make are very elastic, and that attribute isn't really meant for or wanted during the pressurization phase at all. It's for getting the dang thing out afterward, imagine a starfish eating its prey.


----------



## Daniel Thomas (Aug 1, 2015)

I enjoyed the warm weather today and took the fatbike for a ride on a nearby trail. The trail does not have much in terms of interesting technical parts, but in the current dry conditions allows for nice speed in some passages. I borrowed a Garmin Virb camera and tried it for the first time today. Had a fun ride, going at the highest speed I feel is reasonably safe. The bike worked fine, I call it a success with room for improvement!

I also learned that the huge tires do not help with grip when trying to ride a small wet and icy creek. It was still fun.


----------



## Daniel Thomas (Aug 1, 2015)

I have started the preparations for the second run. I want to make some improvements compared to the first frame. The first improvement concerns the dropouts. On the first frame, I used a solid thread rod and electrode-welded it on the dropout. I don't have any other welding machines and I barely know how to operate the one I got. 
This time, the threaded rod is replaced by 12 mm diameter steel tubing. Let's be honest, using a solid M16 rod is very crude. Because of my lack of welding skill, I asked a co-worker from the machine shop for help. We arranged the pieces on a sketch that I made on paper and he fixed them in place with gas metal arc welding and then used the TIG welder to complete the joining. I suppose it won't win a weldline beauty contest but it is a major improvement over what I did for the first frame.


----------

