I am a beginner/hobbyist builder and am currently building my second bike ever, a gravelbike. The first one i built was a mountainbike where i didnt include any bottle bosses. The project had already taken up too much time and i was just trying to get it finished.
However this time i am trying to make the frame a little more, well better in every way. And as it happens to be a gravel bike, it really should have a way to mount bottle cages.
From what i’ve gathered, from this forum and most other resources, is that most people braze their bottle bosses in.
However i dont have a brazing setup and dont know anyone near me who does, or would be willing to quickly braze some bottle bosses. I tried looking to see if welding them in would be a reasonable option, but i didnt find much information.
Then i found this article; Rivnut Bottle Cage Mounts, Installation and Test - BIKEPACKING.com
I was wondering if someone has experince using rivet nuts in bike frames, or what it would mean for the frame if the bottle bosses were welded in? I seem to have the idea in my head that that would make the downtube weaker?
I would avoid it because there is a better workaround. But they are common practice on lower end mass market steel bikes and every aluminum bike uses a version of RivNuts. I installed a set in an aluminum frame and they have always made me nervous.
I was in your situation when I started building and bought a craft detail Mapp torch to do my bosses. It worked great for the job. I also tried with a regular propane plumbers torch but the heat wasn’t focused enough.
This is the torch I used.
I also think this would be better
RTMMFG Oxygen MAPP Torch Kit Portable Cylinder Metal Stand, for Soldering, Brazing, Sparker, Protection glass, Extra nozzle(Gas Cylinders Not Included) Amazon.com
Agree with Brad, avoid the rivnuts. They have their place but not when you are building a frame from scratch. You’ll end of with a crack eventually. Get a a small torch setup and use silver to braze the bosses in. You’ll find a plumbers gas bottle will work well with silver. You’ll need more concentrated heat if you are going to use bronze…and use reinforcments! Whether you get the diamond shaped ones or even a curved washer. It takes no effort amd ensures you’ll never have an issue from botlle bosses and thin tube walls.
Total agreement with @Brad and @DEVLINCC Full disclosure, we manufacture and sell water bottle bosses, so take that with a grain of salt. If you must use a rivnut, I’ve heard of builders using epoxy when installing. I have no personal experience with this, but it sounds like a good idea. #beltandsuspenders#cheapinsurance
Because I am not sure this horse is dead yet, don’t use rivnuts. As mentioned above, a small MAPP gas kit from the local hardware store will do plenty of bosses.
I’ve used rivnuts to add bottle bosses to old steel frames, and I’ve used them to repair frames that have them stripped out. They work fine, but should probably be more of a fix-it solution than an original design intent.
If you want to weld them in, Check out our MS2018 bottle boss. These are intended to weld. You see in the picture there is a little flange at the base of the top radius. This was designed with intent for that flange to be the material that you use to fuse the boss in place, that way you don’t have to add filler wire on such a tiny part.
On my next frame I am planning to flow drill and roll tap in threads for bottle bosses. I bought various size flow drills and taps off AliExpress. I’ve done a couple test pieces but not a frame yet.
Metric as in for the hole size? That’s what the 1/4" refers too. The OD on the one Dave recommends is 3/8" and it’s threaded M5 x 0.8 which is standard for bottle bosses.
Agree on the MAPP torch, I have used it for this exact reason and worked perfectly, a torch, flux and silver wire will cost you as much as a basic rivnut tool.
