CF or Glass Fiber over PVC Pipe

LewTwo

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Hmmmm ....

Just trying to consider this in the worn coffee grinder that passes for my mind. For the sake of discussion this is regarding a more or less generic double triangle frame. Has anyone seen any reference to the number of layers and or weight of carbon fiber and/or glass fiber required for structural components (tubes) of a bicycle frame? Also is there a significant difference in strength or other attributes between epoxy and polyester resins?

The concept is to use standard PVC pipe to form a frame via 3D printed internal lugs. Then wrap the assembly with CF or Glass tape and resin ... no vacuum forming. Of course the headtube, bottom bracket and rear dropouts would need to be metal (aluminum for weight or steel for strength). The PVC and lugs would be considered to contribute little to no strength to the assembly.

I note that a heat gun could be used on the PVC to do some reshaping of the PVC such as flattening the rear chain stays a bit. Most PVC is nominal 40 weight but 20 and 10 are also available via special order?

Thoughts, comments or flames .... :roll: :?: :idea:
 
Great idea. How about using foam for the core instead of pvc tubing to be lighter?

What are you going to do to orient the metal parts in the frame?

I don’t know if their stories are out on the web anymore but they made carbon frames from foam, at least one did and I forget for sure the other. He tried to melt it out with acetone and it just ended up heavier.


He laid on the wetted carbon onto it and then after layering large parts of the bike he wrapped it in electrical tape that had pin holes to get out the excess resin. I think that’s you’re only challenge beyond making the whole thing in plastic or whatever first. I think it’s beyond a weight savings and the carbon is more brittle with too much resin.

Years later it was still running and it was light and looked very nice. A mountain bike.

its like paper mache. In my experience making things. Just need a form to make it on. A mold.


Just need to isolate the metal parts from galvanic corrosion


An integrated seat post seems easier and use an off the shelf part.

Maybe add a couple strands of Kevlar for backup in case it snaps.

Surely u could do some simple strength testing!! Get some sacrificial frame, maybe carbon steel or aluminum or get all three, and figure some repeatable stresses and crush them, then crush yours sadly and make another 😞

Report back on how it goes.


Was going to make a jig w plans online but found them done in metal for like 700$. But didn’t get it.


But the pvc and printed connectors sounds good. If u can get it straight. Be good if u could make a simple jig.
 

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You can bend PVC by capping one end, filling it with sand that has been heated in an old oven, placing it in a form, then letting it cool overnight in the new shape. Search youtube for tutorials.

I like this idea. If you use the thinnest type of PVC, it would so light that we wouldn't really need to dissolve it as I have seen on other projects. People who build with Carbon-Fiber are often "weight weenies", and want to shave any ounces that they can.

I would even consider using bamboo for the seat-tube, just for fun.
 
spinningmagnets said:
I like this idea. If you use the thinnest type of PVC, it would so light that we wouldn't really need to dissolve it as I have seen on other projects. People who build with Carbon-Fiber are often "weight weenies", and want to shave any ounces that they can.

For reference here is a good table of the sizes, wall thicknesses and weights for PVC pipe: https://flexpvc.com/Reference/FullPVCPipeChart.shtml

While I like obviously like the "weight weenie" concept, this is more about being able to fabricate a frame without the need of a lot of space or equipment. A simple way to model and test a particular frame configuration. Crushing or bending or strength testing requires both space and equipment. There have been enough CF and glass fiber bicycle frames built that there must be some empirical data somewhere.
 
LewTwo said:
While I like obviously like the "weight weenie" concept, this is more about being able to fabricate a frame without the need of a lot of space or equipment. A simple way to model and test a particular frame configuration.
I might suggest that apart from some very special custom frames ( recumbent ,speed trials, etc) many of the DIY CF frames are just keen hobbyists working with new materials and new techniques....more of a learning/ interest thing, than the only way to build the frame they want !
Unless you have some unusual ideas that only CF could supply, there is not a compelling reason to risk experimenting with materials and processes...it the ultimate objective is to realise a sound reliable frame.
Weight wise, its speculative. Certainly its known that there is little weight advantage building a frame in Al compared to steel, and i suspect a prototype CF frame would have little advantage also.
So if you just want a convenient way to build one or more frames, it is very hard to go past a good Tig/mig welder and careful choice of correct steel tubing.
JMHO!
 
spinningmagnets said:
You can bend PVC by capping one end, filling it with sand that has been heated in an old oven, placing it in a form, then letting it cool overnight in the new shape. Search youtube for tutorials.

Or you can just quench it in cold water and it'll cool nearly immediately. I made some ~35 lb DIY kettlebells out of some cheap basketballs, concrete, and 1" schedule 40. After a year of usage, they're still holding up great. And if you don't have sand, you can use salt - the melting point is way higher than an oven can reach.
 
Hillhater said:
So if you just want a convenient way to build one or more frames, it is very hard to go past a good Tig/mig welder and careful choice of correct steel tubing.
You may be correct if one has the space, the power, skills and funds.
 
Making a carbon frame is maybe ironically the cheapest and needing the least knowledge and skills method to make a frame. There’s no tools needed other than a basic jig. It’s paper mache essentially. Forget weight savings and still likely cheaper n easier. The next easiest method seems brazing. And epoxy resin doesn’t smell much and silent construction; you could do it in ur city apartment

But how u going to hook a motor up? Maybe decide your layup of material based on that. Maybe do all fiberglass and save money and who cares about weight.


excited to see what u come up with.
 
Hummina Shadeeba said:
.... you could do it in ur city apartment
Exactly

The next easiest method seems brazing.
Done some of that in the past. That would likely be my first choice but one still needs the proper equipment to mill/cope the joints. Also helps to have a rigid jig so that things do not move when the joints cool down. TIG bronze brazing on stainless steel looks really nice. Alas that requires even more space and equipment.

But how u going to hook a motor up?
Standard bicycle wheel and hub motor (front).
 
Hillhater said:
Unless you have some unusual ideas ....
... and therein lies the problem :oops:

It occurs to me one might construct a simple wooden mold, heat some nominal 2" schedule 40 pipe and compress it down into something that resembles a rectangular tube that is 1.25 by 2.813 inches. Those tubes could then be bent to shape. A pair of them back to back might form a 'strong back' frame that could then be wrapped with fiberglass and/or carbon fiber. The structure is similar in concept to what has been used for small mopeds. Thus this is my concept sketch:
CF over PVC Bike Layout (rev 0)2048.jpg
It is modeled using components for which I had dimensions or on hand that I could accurately measure. Those include 24 inch wheels, 24x2 tires, IGH rear hub with drum brake, front hub with drum brake, one inch steerer 'pogo stick', triple tree front fork for a 24 wheel, Bafang BBS02 mid drive. It would of course be simple to substitute a front hub motor instead of the mid drive.

This is NOT intended to be a rough terrain or trail bike. It is intended to be a city or commuter bike that emphasizes a comfortable riding position/posture with the advantages of a 'crank forward', 'step through' design. It is intended to be more practical than sexy. The rider position as shown is just at the leading edge of rear wheel. I estimate that the seat may be raised or lowered to accommodate full leg extension between 26 and 36 inches with standard 170mm crank arms. Some adaptation might be made to the seat post/tube to accommodate shorter or taller riders.

The concept includes bolting steel dropouts to the outside of the rear frame sections but that is dependent on that portion of the frame sitting above the rear hub, chain and bottom bracket. If one wanted to use a rear motor hub and/or derailleur system then the dropouts would likely need to bolted to the inside and the frame width adjusted accordingly. Having all these components hanging underneath the frame means the chain does not need to be "broken" to be installed or removed. It also allows the possibility of a belt drive to be installed. I will not speculate on what the effect of required belt tension for that distance would do the service life of a mid drive. I note also that there is adequate room to install a jack shaft and/or a 'stoker' motor.

That vertical portion of the rear rack is intended to allow the bike to be position on its ass end for service. However the narrow width of the rear frame would likely require some sort of struts or outriggers for that to be practical. There may be a bit of a problem with "toe hit". There is one inch of clearance in front of the pedal with the front wheel in the center. This increases a bit as wheel is rotated to either left or right. This is revision zero ... might need to move the BB back one inch in the next revision to eliminate this potential problem.

That is about 10 feet (or seven pounds) of PVC pipe.

Thoughts, comments and/or flames welcomed.
 
Subscribed.
LewTwo, don't know that you would need Sched 40 tubes. Assuming the tubes essentially form an armature for the fiberglass or carbon, which give the real strength in the build, then really the tubes only need to be stiff enough to support themselves during the build process without flexing all over. Sched 20 might suffice, at a heck of a weight savings.
By the way, the bamboo / hemp / epoxy bike I built a few years back has held up amazingly well!
No cracking or breakage, even after a radical climate change (CA to Florida).
Heresy, but I de-electrified it after moving here ... there are no local hills, and leg power is proving adequate so far.
 
Schedule 40 pipe is easy to come by. Weight savings for thin wall would be about 50% of the pvc (3.5 pounds).
Nominal 2 Inch PVC pipe(1024).jpg
A bigger advantage is it is likely easier to "compress".
Price is roughly the same when ordered online.

There is also something called vacuum pipe used in vacuum systems but I have not found good specifications on it.
 
A bit of fine tuning on the design .. no more toe-kick problems. Gone is the rear stand concept.
CF over PVC Bike Layout (rev A)1280.jpg

If I were to extend the rack up to the seat post, add side panels and a slab seat then it might look a bit more like a "moped" :?
I could work on the aesthetics but I think I prefer the bicycle version.
Electric Moped(1024).jpg
 
Hummina Shadeeba said:
Making a carbon frame is maybe ironically the cheapest and needing the least knowledge and skills method to make a frame.

Go for it, ride the resulting frame for a while, and report back whether you still think that.
 
Hummina Shadeeba said:
What’s holding on the rear wheel?
NUTS :!:
Well usually nuts are used. Actually I think you are asking about the dropouts that I have not drawn in the side view (a set are shown in the plan view). Flat plates bolted to the outside of composite frame. I was actually thinking about pivot plates on something like a 1/2 inch pin embedded in the frame.
 
Chalo said:
Hummina Shadeeba said:
Making a carbon frame is maybe ironically the cheapest and needing the least knowledge and skills method to make a frame.

Go for it, ride the resulting frame for a while, and report back whether you still think that.
Well I keep coming back to the question: "How many layers are needed?"
I have CF handlebars that that have wall thickness of less than 1/32 inch.
Seems a tad thin for the frame to me.

Then there are nagging little problems like being able to finish off the ends of the steerer tube as well as the BB.
Much less work/risk to just buy a frame and hang a motor and battery on it ... but one does need to exercise one's mind.
 
Chalo said:
Hummina Shadeeba said:
Making a carbon frame is maybe ironically the cheapest and needing the least knowledge and skills method to make a frame.

Go for it, ride the resulting frame for a while, and report back whether you still think that.

I base that on having found guides to making a diy carbon frame going years back now. I look now and there’s even more. Some of them do update how the bikes are doing years later or they do destruction tests. I still believe it’s the easiest way to make a frame. I came close to doing it. Ive made a bunch of other fiberglass and carbon stuff like fenders and skate decks.



I don’t see anything for the rear wheel to bolt to anywhere. What’s the plan for the frame structure? A standard bike frame sounds best.


Some of the guides talk about how many layers of such and such fabric but I imagine stiffness would parallel the strength, assuming you use the right ratio of carbon to resin to not make it brittle, and you could compare against some other carbon frame.
 
I don’t see how the sleeves would be good for a typical layup method. If u could pull them taut like a Chinese finger trap tight onto the pvc that would be great but I can’t imagine that’s possible with the multiple tubes, otherwise ur laying it on like u would normally which is like paper mache.
 
Tubes would likely be useful for the first layer before anything is joined together. Once there are joints involved I would agree that hand layup is likely more beneficial. Hand layup also allows one the build in extra layers for example on the top and bottom as well as joints.

Price wise, glass is a lot less expensive than carbon or aramid but one needs to account for the extra material, resin and labor involved for additional layers. My design also needs to be adjusted to account for the thickness of the fiber and resin ... still the major unknown in the equation.

Someone used to sell a type of plastic tape to wrap around hand layups such as this. It had a grid of pin holes for the excess resin to seep out as the tape applied pressure to the surface of the workpiece. I have not seen that available for some time.
 
Hummina Shadeeba said:
What’s the plan for the frame structure?

You are looking at it.

A standard bike frame sounds best.
A lot less work/risk/(possibly money as well) to just purchase a "standard bike frame"
 
Chambers said:
LewTwo said:
Someone used to sell a type of plastic tape to wrap around hand layups such as this. It had a grid of pin holes for the excess resin to seep out as the tape applied pressure to the surface of the workpiece. I have not seen that available for some time.

Perforated shrink tape
https://shop1.r-g.de/en/art/390450-P
Thank thee :thumb:
 
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