carbon construction techniques?
can anyone point me at a discussion of the various carbon construction methods (tube-to-tube, monocoque, lugged, other)?
i'm a metal guy with a respectable stable, and i'm contemplating adding the first plastic frame. surprised to see that many of the highest-end frames are lugged. just looking to get schooled...
Much like with a steel frame, the joining method is not very important. Clear evidence of this is in the marketplace; there are high quality frames using all the basic methods.
Originally Posted by dookie
yeah, ok...but there has to be a reason a builder does what they do. take your steel example...lugged/brazed is generally done for the low temperature and/or aesthetics, fillet is heavy but gorgeous, TIG is quick but not applicable to all steel (and necessary for some), etc.
Originally Posted by Nessism
so, why are highest-end carbon bikes often lugged? it would seem (to this layman) that monocoque would be best suited to take advantage of the material properties but also the most difficult, yet many low-end frames are monocoque?
i'm not looking for a 'which frame to buy' recommendation, nor a market analysis...just a basic understanding of the hows and whys of the methods.
I think some people assume that monocoqote would be best but it's mostly just a small detail in the grand scheme. The Trek carbon frames for example have some very elaborate lugs, which are more like frame sections in places. I don't see how making the frame in one piece would be an improvement. In fact, a one piece frame is more likely to have manufacturing flaws since the construction technique is less forgiving due to the size and complexity of each layup.
Originally Posted by dookie
I'd encourage you to not over think details like this. Much like a steel frame, the joining method is unimportant other than with regard to visual appearance.
what can i say? i'm an engineer by trade (but not composite/materials). it is my very nature to overthink the details...
Insane Bicycle Mechanic
Lugs for carbon frames make it easier to customize the geometry. A monocoque frame requires dedicated molds for each different frame variation- a very expensive proposition. Lugged construction allows for infinite variations, like this Calfee tandem and this carbon recumbent.
Originally Posted by dookie
Once you've constructed the molds for a monocoque frame, you can ship them to whereever the labor is cheap and have them crank out thousands. That's why "low-end" carbon frames are monocoque.
Last edited by Jeff Wills; 03-20-09 at 12:11 AM.
Well, low end and high ends are monocoque. Yes, it is easy to make a monocoque cheapie however the art of the monocoque is in the lay up of the fibers and choosing the right material at the right point on the frame. tubular frames are great and have their place too. the truth is all 3 construction methods : monocoque, lugged, and tube to tube all have valid applications and each has a unique feel to it.
Calfee has a discussion of this on his site:
It's not a composite engineer's paper but is a good overview and I think is what you are looking for.
Good overview of Brano Meres' first carbon frame.
One of Sheldon Brown's friend's article, "How I Made a
Carbon Fiber Bike in My Garage
by Damon Rinard"
Your best supplier for carbon supplies:
The techniques for building carbon bikes filtered directly from the homebuilt aircraft industry.
Lots and lots of useful stuff at Aircraft Spruce. They also have carbon tubes and vacuum pumps.
If you don't want to build your own rear triangle you can order one from Ceeway:
You can also order a carbon kit where all you have to do is cut your tubes to size your frame and glue the parts together.
And as a tip I've found that it is easier to form neat lugs with TOW carbon than having to cut cloth to fit well around complex shapes (seat post cluster for example).
List of good books.
The first, VACUUM BAGGING TECHNIQUES, is well worth the five bucks.
COMPOSITE BASICS, is also worth picking up.
Last edited by Allen; 06-30-09 at 12:25 PM.
A carbon constructed anything (bike frame, boat) gets heavy when you can't get the resin out. If you lay something up in wet cloth or inject resin into molds with cloth inside (big boats), you got to sweeze most of it out of the part with pressure in an autoclave.
The vacuum bags you've no doubt seen on web sites are forcing the carbon cloth into the mold, as well as, removing excess resin which is superfluous to the strength.
I suspect lug is popular because you can more closely control the resin in a part (thus weight) in both lugs and tubes... more precise than trying to squeeze every last drop out of a laid up frame.
Personally I think the lugged carbon frames ride way better than a monocoque frame. Before i started building my own steel frames I would choose a Look carbon/lugged frame over any bike out there. May be that they worked well for me or just a personal opinion however I still believe they are the best carbon bikes made. The 595 is a beautiful frame, I wish I would have built it. Look has been way ahead of everyone when it comes to carbon.
There is a convention factor also. People who want carbon frames may want to merely have the degree of change substituting materials in the tubes will create. Going to a monocoque is a whole other discussion.
Monocoque is a good way to build certain structures where surfaces and structure are in close alignment, But in other cases a less zowie approach may work out better. Compare the all carbon wheel, to the equal quality conventional wheel with a lightweight fairing over it for aero. You can actually be better off with the rag and stick approach of the latter, compared to the aero carbon wheel, when there isn't a regulatory bias agains fairings.