What even is it?
For my project, I’m building a bicycle frame. I’m trying to use a technology that was the cream of the crop during the late 80s and early 90s. Lugged carbon fiber. This process is essentially the use of metal to make the corners of the frame with carbon tubing adhered between them. For those who know this, it is classically 90s. There have been some boutique remakes which look distinctly modern. Also, LOOK brand continued making lugged carbon frames for a while. Unlike the 90s though, the frames had fully matched paint.
Functionally, I’d like to make a bike with a modern geometry and part compatibility. I want it to be very strong, and if at all possible very light.
Aesthetically, I want it to look classic. In the spirit of the 90s, nothing will be downplayed. The few contemporary lugged carbon frames generally look subtle and subdued. The 90s wasn’t about that. The colors were bright, the patterns were brazen. The lugs will the long and pronounced (largely a structural decision) and brightly colored, with curved ends.
How did I think of it?
Oh, I didn’t. It’s all been done before, just probably not in this combination. I’ve written an inspiration piece here.
In addition to strong appeals to 90s retro, I want to capture the functional and aesthetic appeal of the modern cargo bike.
Everything I’ve said so far is shallow and frivolous, (you could say it takes after its creator) and I’d like to add a practical side. I’ve always loved Jeeps. Particularly the Cherokee. It has a rugged appearance and can go everywhere, all the while being more handsome than most cars on the road. The cargo bike brings a stout and stable frame with voluminous tires. Disc brake tabs as well. If I could combine an impractical aesthetic with a purely practical vehicle, I think I would have something genuinely enjoyable to use and own. Additionally, these kinds of bikes are great for distance riding, which would allow me to explore the aesthetics of the world at ground level.
In the end, I want people to look at the bike. Let’s be real. Nobody carefully examines bikes, unless they’re interested. And those bike enthusiasts really only look long enough to identify make and model and profile the rider. People who don’t know bikes just see bikes. Unless you’re riding two bike welded together or something. Otherwise, stares are rare.
I want a bike that the longer you look at it, the weirder it is. All the while, I want it to be practical. I’m not doing outwardly complex geometries. I just want to place a bunch of eye catchers across the frame.
For general audiences, each lugged corner will be a different color. The colors will be hot and fluorescent in the front, and cool towards the rear. The headtube for example would perhaps be neon red. The seattube top neon yellow. The BB, green. Finally, the dropouts will be blue. The idea is as the eye moves through the colors, they go from most attention getting to least. They will start the the front and at the rider, and move down and rear. I think this will add a quality of motion, looking fast standing still.
The bike lovers, the bike will be like nothing they’ve seen. A touring geometry, capable of supporting 29×2.2 in tires. Disc brakes. Lugged carbon, a technology unused since long before disc brakes and 29in tires. I want it to look like a very handsome Frankenstein, like a resuscitated Yul Brynner. You’ll just ask “Is this for real?”
Anyway, I can dream.
The technical mire
This an ambitious project, period. The geometry is decided upon, but the actual configuration of tubing, the dropouts and the yoke are yet to be dimensioned. I need to learn to weld. Or find a brazing torch. All these things I have started only to the degree that I understand the risk.
The real kicker is the carbon fiber. It’s expensive! Really expensive. If you want carbon fiber tubing, good luck finding anything custom that suits the lugs and tubing you can also find. And if you do (I did) expect to pay $50 a foot. Or more.
My friend however has a roll of the stuff. Dry, woven fiber. He’s offered to give me a really good rate on it. Not that it’s even that horribly expensive. You don’t need a lot, the strength is remarkable when done right. However, doing it right is proving to be hard. After doing research on a number of processes, I’ve rigged a device that allows you to mold around PVC pipe. My first attempt using crap hardware store epoxy went like this.
For a first try, not bad. Only 4 layers thick on the left and 2 layers thick on the right. I wanted to experiment with variable layer thickness to make sure I can reinforce my tubing at the ends. In the middle and left side, this piece is so strong it cannot be broken with the bare hands. Maybe if stomped.
There are however weak points, driving a thumb into the unlaminated left end will probably break it. There are obvious bubbles in suspension, probably not good for strength. I attributed most of the problems to high epoxy viscosity.
To test this, I laid up 4 layers of fiber with epoxy heated over steam.
The finish on this piece was shiny and almost completely uniform. The only obvious exception is this bubble centered on the piece in the picture above. I suspect that can be eliminated by painting the outermost surface with epoxy, rather than hoping it will soak. The seam of the fiber is visible here, indicating that this was the end of the fiber sheet. The bubble may have been caused by the epoxy removed by my thumb when I held the fiber here.
Another considerable change is thickness. The 4 ply section in the first piece had 2.5mm thick walls. This piece was under 1mm in most places. This suggests increased fiber density and the potential for improved strength to weight.
In the meantime, I plan to refine the molding device. Hopefully I’ll be able to make more test tubing with it by the time my carbon fiber specific epoxy arrives in early March.
The bad part
The epoxy cost $60, and may not be enough. The tubing and lugs have cost about $120 so far. The steel from which I will mill the yoke and dropouts will cost about $35 before shipping. $50 on fiber. However, that is about it. A bit over $250, and if everything goes right I will have something big crossed off my bucket list. If it means the difference between good results I can ride everyday, and barely making it, I’m willing to dump $350 into it. If it’s exceeding my expectations, but needing substantial rework, maybe $400. If I play my cards right, that’s a still steal for a custom carbon frame. I’m designing it to be fully compatible with parts I already have, so I only need to part out my commuter to finish this.
This is going to take a long time. I’ve started research and analysis about 2 weeks ago. Most ordering is complete.
END DATE GOAL REMARKS
3/6 Revised mold Will require machining
3/13 Test sections Make CF test sections for destructive test
3/20 Finalize geometry Start dimensioning parts.
3/21 Start tubing With geometry known, lay up 1 tube a day.
3/27 Finish components Tubing and lug sections manufactured.
4/3 Jig built 3D printed jigs for epoxying all parts.
4/10 Parts joined Glue it all together.
4/13 Begin assembly 72 hrs for curing.
Admittedly, this an a death march of a schedule. A major accomplishment every week. Combine that with work and 9 credit hours of graduate coursework and we’ll see how it holds up. A lot of this work can be done concurrently. Geometry is already in the work. After the mold is done, each test segment will take 30 minutes to make with 24 hours of cure time. The jig should only take a few design hours. While I think I’ve chosen a nearly impossible task, I believe that the tremendous resource of the school and my peers, combined with my maniacal zealotry give me a fighting chance.
If anyone knows any of the ins and outs of the machine shop, let me know. A lot is riding on reasonable turnaround time there (3 days for a 2x4x0.25 steel part).
I still love the idea of this project. i have a little concern less in the failure of the tubes from stress but more for their connection to the lugs (how will things like temperature, humidity… effect this). Also would be worried about taking this mountain biking but maybe I just crash more than most people.
My calculations indicate over 5000 pounds of compressive/tensile force tolerated by the epoxy junctions in the front triangle and 3000 in the rear. I don’t think the stress will ever be concentrated enough on one junction.
Also I’m building less of a mountain bike and more of a bikepacker’s bike. It will be offroaded, but most of the strain will be camping gear.
I’ve called the tech support for a couple companies that sell epoxies used in composites and bought what they recommended for my application.
Off by a factor of 3. 15000 and 9000 lbs. The steel tubing is 10000 pounds in tension and intended for BMX bikes.
Also using a bond line controller, which is essentially a bunch of 4 thou glass beads that ensure concentricity of the tubes.
This is definitely an ambitious project. I am really interested in how you create these carbon fiber matrices. I am in a composites class right now so if you want any help I may be able to assist you.
I like how clear your 90’s aesthetic is. So far this class, describing my aesthetic has been pretty difficult for me, but it seems so natural to you. I also think it is great how you have been able to work with new technologies and pick up on them so quickly.
Dean cycles in Gunbarrel, right off 119, is a local custom bike builder who may be able to expend some advice in the frame construction. They normally work in Titanium but have been building for 25 years so I bet they’ve seen it all. Might help avoid any pitfalls as the budget is tight.
Ryan has a great point in saying that finding someone who might have done this before would be a great resource! I am pretty sure that Boulder Bikesmith on 30th Street has done some custom bike work and also might be able to provide some pointers.