For folks who do carbon fiber work, what do you use for M5 bottle boss “braze-ons”?
I know riv-nuts are common, but I’m not in love with how inelegant they seem. Is that something I need to get over or is there a better way?
I have been playing around with the idea of a 3D printed glue-on boss, either external or internal to the mating tube. It seems like there should be enough surface area to support a decent amount of weight but I could be wrong about that.
I’ve been thinking about something along the same lines.
3D-printed one-piece construction that glues on from the inside. Extra surface area provided by ‘wings’ around each boss and a rib between the two to provide even more surface area for the adhesive.
The super high end epoxies available on the market now should provide more than sufficient adhesion as long as surface prep is done right.
That’s a great design element. Nice.
I saw someone’s Instagram story recently (Frameworkbike?) where they use riv nuts but epoxy in a brace on the inside to take the load and not put stress on the carbon directly. I’ve sent him a message to see if it was him.
Yeah that’s how he does it. I think it’s not a bad solution, but at the same time i feel one might just as well machine a thread into the brace and just count on the bonding, instead of having that rivnut still in there.
Other than that i did bond a stainless steel nut with what’s basically a composite nut plate on the inside of the downtube of my road bike. That worked out really well. So can’t see how this would be any worse.
This is something I mulled over for a long time and I looked at lots of the solutions that big manufacturers and other builders have used.
After a lot of thinking I came to the conclusion that rivnuts have become the defacto because they are simply the most ideal solution. Engineering is about balancing all of the requirements of a part and low complexity and low cost will win almost every single time. Rivnuts are also easily repairable versus a bespoke solution.
So for my builds I just ensure that I have some extra material laid up on the inside and outside of the rivnut location. I suppose this is harder for your project as you are buying off the shelf tubes so you can’t do that as easily.
I hate to discourage innovation. So don’t let me stop you! Just adding my thoughts.
Edit:
Saying that I have yet to experiment with loading up a cargo cage onto rivnut bosses. But there isn’t a great deal of cargo that is denser than water. So if it can hold a full water bottle then I’m not too worried.
