PolyTube Cycles

[datas_brother]

Restlessness!

I’ve never spent more than 5 years in any one place my entire life. Even as a kid, I almost never went to the same school for more than a year. Although my desire for change has slowed over the years it hasn’t gone away. I’m now 41 and my wife and I spent some time thinking what to do next. She suggested that since I love cycling I could takeover an LBS from someone going into retirement. That was the spark. I thought “I want a new bike - why don’t I just make one.” I’m a firm believer in being able to do anything if you put enough passion and thought into it.

To turn the idea into reality, I started thinking about what I wanted in a bike. The shortlist was:

Lateral and torsional stiffness
Comfortable
Custom sized
Light
Carbon

Wanting it to be made of carbon didn’t make things easier. All of these companies spending hundreds of thousands of dollars on R&D put the first doubts in my head. I had never worked with the stuff and maybe this naive viewpoint is what allowed me to continue. After a bit of research, hearing all the stories of CF bikes falling apart under the rider without warning or frames ruined because they fell over on a bike rack, I soon added bombproof to the list above.

The last 5 years have been spent working toward the goal of starting the business that I just registered in April. I’m not yet building frames for the public yet but that will come soon. After developing the prototype that I ride regularly, I started to think about all of the test materials I’ve destroyed and how carbon has a reputation of being fragile and non-repairable. I started fixing some of those test pieces and found that I could make them just as strong as the originals without adding too much weight. It was time to try it on a real bike.

I’ve spent the last 15 years working in quality assurance and have seen many examples of theory going terribly wrong when put into practice. So, I chose to test systematically before starting. Getting broken bikes turned out much easier than I thought it would be. It took one add in a German cycling magazine and I got so many offers from people, who had accidents that I was turning away many more then I could handle. I chose a number of frames with different types of damage and went to work. I’ve fixed all but one of them. The last one will be special but more on that later. The repaired frames were sent to a testing laboratory where various tests to check the structural stability were performed. All passed. To be sure, the lab also sent them for impulse-thermographic imagery. This is a special testing method that allows you to find defects under the surface, where they could not otherwise be seen. All of the repaired areas showed no problems. In the mean time I’ve started taking on repair jobs. PTC is now open for business.

The name PolyTube Cycles comes from the way I make tubes. I wanted more stiffness then the bike I was riding at the time offered. I’m not a big fan of oversized tubes but looking at the big names, you would think there is no alternative. If you just add material you’ll get a stiffer tube and if you increase the tube diameter, you can make it stiffer without adding material. That makes the tube thinner and more susceptible to impact damage. It’s also ugly to boot! You can change the shape of the bike but then you can’t use it in official events (not that I do any racing, though). The solution I chose is to run several tubes parallel to each other. Of course, it isn’t as simple as that. The tubes needed to be “woven” to each other but if you cut through them it looks like multiple tubes running parallel.

Where am I going? I’ve already started with repairs and will continue with that for awhile. I hate throwing things away and just because a frame is cracked, doesn’t mean it is trash. I really enjoy taking a splintered tube, sanding it down layer for layer and building it back to new. My next step will be some customisation work, which is where the last frame comes in. I’ve never been a fan of external cables and so in addition to the repair I’ll be moving the cables inside and making the frame look anything but like the big box name it started as.

This type of work is fun because no two frames ever have the same damage so you have to start from scratch every time. But, my real goal is to continue with framebuilding, however. I’ll be making some more prototypes and testing them myself as well as having labs verify my results. When I’m confident I’ve got my process down I’ll start offering to the public. I still won’t be giving up my day job any time soon but maybe (hopefully) some day...

[Eric Estlund]

Hi Kevin-

Is there a web site or image site where you have some of your work posted? I'd be interested to see what you have come up with.

[Chauncey Matthews]

Paraphrased: "I make my own carbon fiber tubes in a way that nobody else does"

Where are the pictures? You're killin me here!

[CyclesNoir]

All of this sounds very cool! And I've seen pix before over at the forum, so I know the results look great. It will be interesting to learn more about your poly tubes. Meanwhile, do you use a blader inside the tube when doing repairs?

[datas_brother]

Hi Kevin-

Is there a web site or image site where you have some of your work posted? I'd be interested to see what you have come up with.

Hi Erik,

yes, look at:

Home
Flickr: datas_brother's Photostream

I'll be updating the pictures as soon as I get some of the frames back from the test institute.

Cheers
Kevin

[datas_brother]

Paraphrased: "I make my own carbon fiber tubes in a way that nobody else does"

Where are the pictures? You're killin me here!

Here is an image some tubes I made for testing puposes:



Cheers
Kevin

[datas_brother]

All of this sounds very cool! And I've seen pix before over at the forum, so I know the results look great. It will be interesting to learn more about your poly tubes. Meanwhile, do you use a blader inside the tube when doing repairs?

Up until now I've been working with internal mandrels. I make each tube separately and work T2T. I'm very happy with the results from a structural standpoint but I still want to improve cosmetically. Right now I'm working on a mold, with which I can change tube angles and works with internal bladders. I plan to monoquoc the TT, HT and DT together as well as the CS and SS. The ST and BB are also one piece. This will allow me to make any custom geo and still only have to work T2T at the seat cluster and BB. If all goes as planned, the mold system will be finished and pressure tested by october. I'll spend the winter months making test pieces and some prototype frames for CEN testing.

Looking back at my answer to Chauncey's question I could give a little more detail. If you look at my logo you'll see what my downtube looks like if it were cut. I designed the layup schedule to distribute forces coming from the HT and BB equally among all of the tubes. You can get an idea of how it works with a simple experiment. Take 5 sheets of paper wrap them around a 1" (25mm) mandrel to make a tube. Wrap them one at a time and glue each to the next. Now take another 5 sheets. Wrap 4 of them separately to 1/4" (10mm) tubes. Glue those four together and wrap the fifth around the whole thing. After the glue dries, squeeze both lightly, twist both and finally try and crush them end to end. If you did everything right you'll notice that in all cases the normal tube is easier to deform.

I'm not the best explainer in the world so I hope this is clear enough.

Cheers
Kevin

[datas_brother]

Hi,

This thread seems to be slow going. By far, I'm not the most prolific writer here and so I guess that most of those asking questions on the other SO threads have known each other for awhile and don't know quite how to take me. I've already explained how I came to framebuilding (even if I'm still walking down that path). Here's how I started with cycling.
I spent a couple of years living in a suberb of Denver CO called Broomfield at a time when BMX was the thing. I couldn't afford a real BMX bike so I tried to fake it with some no name kids bike untill the frame broke at the HT from a poorly landed jump. To replace that bike, I was given used Koga-Miata road bike that I loved and road for several years. I don't rember why or when but had to give that bike up. When I decided to join the army in high school, I needed to get fit so I saved my money from working after school and bought a cheap 10 speed at Sears. I gave that bike away before leaving for basic training. I ended up getting stationed in Germany where I got hold of an unmarked steal road bike. I spent hours on it after duty and is really where I got hooked. I was faster than anyone I met on the road so even tried a crit. I failed at that partly because I was racing with non-indexed DT shifters against the new STI bikes but mostly because I wasn't fast enough. I like getting on a bike and just riding for hours and I hate the kind brake and accelerate needed for crit.
I hope this gives a little more insight into who I am and stimulates a few more questions.
Cheers
Kevin

[edoz]

Have you done any complete frames yet? If so, how did they turn out and if not, do you have one in sight?

[datas_brother]

Have you done any complete frames yet? If so, how did they turn out and if not, do you have one in sight?

Yes I have. I did the one you can see on my flickr page. I also did one incomplete frame (no BB or HT inserts), which I destroyed.

I've been very satisfied with the results but I still want improve the cosmetics. I also want to get some independent varification through Velotech before I do anything for other people. I don't like relying on test results from any single source so I test first then have an independent test house confirm that.

Cheers
Kevin

[datas_brother]

Hi,

I just uploaded some new pictures of me in my shop:

Flickr: Polytube-Cycles' Photostream

[roguedog]

Kevin,

Some interesting stuff you're doing.

How did you end up choosing carbon as the material to work with? Why carbon? What is it about the material that draws you? How did you decide on your design? In other words, did you do some research like ask for all broken carbon bikes that folks were going to trash anyway and analyze them? Or is this design a result of your thoughts on how best to improve upon what's out there? Looks like you are well on your way to getting the bike creation part down but there are many other factors to becoming a frame builder. What are your top topics to learn and delve into (or are currently delving into) to round out your frame building skills?

Cool stuff. I kinda like the prototype 1 in a mummy bike type of way :) Maybe you should hook up with Spooky for a run .. heh heh.

Hey.. you did ask for more questions.. :)

[datas_brother]

Kevin,

Some interesting stuff you're doing.

How did you end up choosing carbon as the material to work with? Why carbon? What is it about the material that draws you? How did you decide on your design? In other words, did you do some research like ask for all broken carbon bikes that folks were going to trash anyway and analyze them? Or is this design a result of your thoughts on how best to improve upon what's out there? Looks like you are well on your way to getting the bike creation part down but there are many other factors to becoming a frame builder. What are your top topics to learn and delve into (or are currently delving into) to round out your frame building skills?

Cool stuff. I kinda like the prototype 1 in a mummy bike type of way :) Maybe you should hook up with Spooky for a run .. heh heh.

Hey.. you did ask for more questions.. :)

Wow! those are allot of good questions all at one time. I chose carbon at first for weight reasons. I wanted a very light bike. That focus changed after doing research when I learned how much more CF is capable of. I started to see how much you could do with aesthetics and how strong the material really was. I also realized just going after low frame weight was stupid. It's like buying a Lotus Elise (my favorite car) to go to the grocery store with.

To research it I had to learn several things at one time. How do you design a frame that fits? Where are the highest forces acting on the frame? How do you work with this material? Are just some of the questions needing answers. I started with the material by way of google and the library. Then I started making parts (tubes and joints) to see how they break. I had worked with fiberglass before but carbon is completely different. After doing more research on the physics of bike frames I started making frame parts and breaking them - all the way up to a complete frame. I likely could have bought a half a dozen frames for the cost of materials I've destroyed before making the prototype.

I'm not sure how I came up with the idea of multiple tubes but remember seeing an aluminum heat sink, which had the cooling fins on the inside of the tube. That made it very efficient with out taking up huge amounts of space and I'm sure that influenced me.

What do I still need to learn? Bike fit. I haven't had the advantage of working in a bike shop so I'm learning from scratch. I'm sure that will come with time.

I'm currently working on several things. I just set up a new shop that lets me work through the winter. I'm building a test jig for checking structural stability and will calibrate it to match the results of the test lab I work with. I'm making a mold system that will allow me to build using internal bladders. This has the advantage of a better surface structure.

The prototype looks that way because I wrapped it in Kevlar. I really like the look and have used it on a couple of repairs. It's very challenging to work with because the fiber structure shows on the surface and you can't sand it. You have to have a very good vacuum and a good gel coat on top. If it goes wrong, the part is toast. BTW who's Spooky?

[datas_brother]

Hi,

yesterday I came home to find a huge box waiting for me. It contained 4 frames I had sent for testing to Velotech. All of the frames I had repaired and passed testing.

It also contained the reference fork I use for testing. For some of the tests you need to mount a fork. To reduce variance I use the same fork for all frames. I chose an extra heavy duty steel fork. It alone weighs more than most of the frames I get. One of the tests is a static braking stability test. This is done by mounting dummy axles front and rear and pulling them together with 1600 newtons force (160 kg). This is about the max force a frame would see when making an emergency stop using only the front brake. None of the frames had any issue with this test but the fork is now toast. As you can see from the picture below, it bent both blades leaving almost no rake. For testing purposes, that doesn't matter so I will likely add some reinforcement and keep using it.



I had an ultra light weight Stevens frame and fork tested the same way and it is still ridable.

BTW re-reading this post some might consider this to be a statement that carbon is better than steel. That's not what I'm saying. Neither material is better than the other. It all depends on the person behind the torch/epoxy pot.

[datas_brother]

I'm collaborating with the testing facilities I work with on this website: Carbon Bike Check. It's written in German but will likely be translated into English. I wrote up a short description of the repair process for the site. Here is the English version:

How are carbon fiber frames repaired?

When a carbon fibers are overstressed, they break without deforming. The damage is not always visible but once it starts it will continue to complete failure. This does not have to happen. It is possible to make a broken frame safe again. Although the process is complex it can often result in a bike that is even stronger than the original design. The repair process can be broken down into several steps:

Inspection. First, the damage is assessed via visual inspection. Cracks as measured and documented and an endoscope is used to look at the damaged area inside the frame when possible. The rest of the frame is also checked to ensure no further damage can be seen.

Stiffness testing. The frame is placed in a test fixture and the stiffness of the broken frame is measured. Here the tracking and torsional stiffness values can be used to determine if further damage is likely. If the frame is shown to be weaker than the visible damage would account for, thermographic imagery can be used to show where the hidden damage is.

Exposing the wound. Once all damaged areas have been found they are sanded to remove paint. Then carbon layers are carefully removed in successively smaller areas. This is necessary to avoid any sudden changes in stiffness along the tube. This would cause points of high stress and lead to frame failure after a short time. The lowest layer is left to provide the required surface area to which the new carbon will bond.

Clean-up. The damaged area is then cleared of dust from sanding and degreased to allow a good bond for the new layers.

Planning the lay-up. Based on the lay-up of the manufacturer and where the damage is, a new lay-up schedule is planned that will allow the area to be at least as strong as original without creating bulges or low areas. It is often necessary to use several different types of carbon fiber in order to achieve these goals.

Laying the fibers. Using special epoxies, the fibers are layed down in the predetermined order. The frame is then wrapped and placed under vacuum for the epoxy to cure. The vacuum ensures that the fibers are compacted well and the no air is trapped between the layers.

Finishing preparation. Once the repair has had time to cure, it is unwrapped, sanded and cleaned. The frame is now ready for finishing but first new stiffness values are measured to determine if everything has gone according to plan.

Measuring-up. The frame is again placed in the fixture and the new stiffness values are determined. If all has gone well, these values will now be well within spec.

The finishing touch. Now the frame is painted. This can be as simple as applying a coat of clear leaving the carbon fibers visible. It can also be as complex as a custom air brush design. The fantasy of the owner is the only limit.

[Chauncey Matthews]

OK, I have a couple q's:
1. You said you got back frames that were tested- how are they truly tested without being pushed to the point of failure?
2. Your stiffness test- how do you determine the frame isn't stiff enough? It seems like measurements would vary quite a bit depending on frame design, tube diameter, etc.

thanks!

[datas_brother]

Hi Chauncey,

I hope your doing well.

Both are good questions and difficult to answer without giving away too many secrets.

1. Tested means a series of tests which gives you a picture of the frames properties without causing damage. While none of them is intended to push a frame beyond its limits, some do push it beyond what you would expect to see in real life. An example is the braking stiffness test where you pull the front and back DO together. The applied force is 1600 N. In real life you would not see that much force in that direction unless you hit something. Apply that much force to the brakes and you loss traction. Another example is rear end lateral stiffness. You fix the frame via the BB, put a dummy axle in the rear DO and pull it to the side. here you apply 1000 N which is more than the frame would normally see while riding. In both cases as well as all other stiffness tests you are looking for the amount of deflection caused by the applied force. Carbon is a relatively linear material all the way to ultimate failure so you can tell allot by looking at different stiffness values and how they relate to each other.

2. At first glance you're right but in reality makers tend to aim for specific stiffness windows. They know if you make it too stiff it will feel dead and if you make it too compliant you reduce perceived efficiency. An example is torsional stiffness. Most makers look for a value between 110 - 150 Nm/deg. This is a value that manufacturers advertise with and magazines test and compare frames with. It's also one of the easiest to test. If the value is too low the frame is likely unsafe. Too be sure, you have to compare this value with those you get from other tests. This gives you a complete picture. If fibers are broken, the frame will go soft and show more deflection. Usually this is black or white but if you end in the gray area you need to do additional testing to find out why. This can be computer tomography, or impulse thermography. Both of these methods can tell you precisely were any damage is.

Does that answer your questions well enough?

[Chauncey Matthews]

Perfect. I find the carbon end of things quite interesting.
Thanks for the info!

[CyclesNoir]

Its fascinating to read your approach to diagnostics, design, and building!

Cool stuff.

[datas_brother]

Thanks Rick.

BTW part of that design philosophy is using what I have at hand whenever possible. The extrusion Al that I'm using for the test rig I posted on FNL is left over from the solar array I installed on my roof a few months ago.