prairiepedaler

Came across this article today >>> https://bikepacking.com/gear/rivnut-...unts/#comments

The author modded his fork to include mounts for a bikepacking cage. Although brazing in a mount is preferable, anyone else try this sort of thing on their frame or fork?

I recently had both barrel type bosses snap off the rear seat stays on my current ride. I am not suggesting I try this rivnut trick to replace them but it provoke some thoughts. These barrels were just barely tacked on top and bottom. A Kuwahara frame is usually decent quality but you could see where much more welding rod could have been used between the barrel and tubing. I'll take a snap of them for show and tell.

Andrew R Stewart 

I've installed a number of Rivnuts, both as replacement for "bad" ones and to add more bottle cage mounts. I've never liked them but do work with them when called for. The lack of really solid connection to the tube they are pressed into, their usual soft metal (so to make the setting able to be done via a hand tool) and they seem to corrode faster than a brazed in boss does are all demerits in my world. Setting into a steel frame is their worst application IMO. The hard steel won't take the bite of the Rivnut's serrations well and the less curved the tube is the less 3rd dimension the Rivnut is grabbing onto. For steel frames I will usually add some slow setting epoxy around the rivnut's body (and the tube's hole) before setting it.

I would not suggest a Rivnut for a rack mount if the rack will carry any real weight. When I read of the stay rack mounts breaking off I wished for a photo but your description describes the situation very well, thanks. I suspect the tiny welds were done fairly "cold" and didn't really meld fully with the stay. Were you able to see the weld bead remaining on the tube or the boss? Welding has it's place but doing tiny bosses and bits with it isn't one, IMO. Had the rack been used for a long time and/or with a lot of weight? Did the rack have any triangulation for side sway (like Blackburn's Expedition rack)? The number one way to break off a boss is to flex it repeatedly. Thankfully "P" clamps are available in many sizes. Andy

prairiepedaler

Hi Andy, thank you for the input. I definetely would not be using a rivnut for a rear rack. They would certinaly not be strong enough. Attached is a photo of the barrels. I don't have a car and use the bike a lot, sometimes with a significant amount of weight in the rear. Also, in the winter the roads are bumpy with uneven ice/hardpack which contributes to metal fatigue. Personally, I think that threaded rear rack stay braze-on mounts done in an internal-to-the-stay itself is far superior - but, is undoubtedly harder to do and therefore more expensive. I had a Raleigh Elkhorn which was built with this arrangement. P-clamps are now already in place. The barrels didn't both fail simultaneously. I kept an extra P-clamp bolted to the stay to carry along in case the other side failed out in the field. I have a bunch of NOS cushioned P-clamps but none of them are the right diameter unfortunately. Those would have been perfect.

Andrew R Stewart 

The stay bosses are pretty much what I was expecting, the welds didn't fully penetrate into the stays. Given the use you describe it's not surprising to see these breaking off. You can see the rust had gotten into the weld tacks quite a while ago.

For my own rear rack mounts I prefer they have a threaded through hole. I make my own or use the "tombstone" type that are commercially made. The through hole allows for easier makeshift field repairs as well as possible locknuts additional to any boss threads. Most of the frames I have made are on the small side and having the stay bosses along the sides of the stays mean that the rack struts become really long. So I use a stand off position. Andy

bulgie 

I put riv-nuts into my forkblades for a small rack for a handlebar bag. On an old road bike I didn't care much about, that I used for commuting. Blades are 1.0 mm thick Cr-Mo (Tange) Probably wouldn't do that for a customer due to liability concerns, but I actually think it's safe. Problem is, for a customer you need to KNOW it's safe.

I used rivnuts made of some nickel alloy, I forget, probably Monel. Benefits include corrosion-resistance and high strength. The were difficult but still possible to install with just a high-strength bolt with nuts threaded on, my usual way since I don't have a setter tool. Before you ask — no, I don't know where I got them. Still have a few, but there's no brand or source info on them.

Did that in the '90s and I still ride that bike a fair bit. Loads have been mostly under 10 lb, occasionally more like when I set a grocery bag on there with bottles and canned goods. I know the rack and rivnuts can hold over 200 lb static load, because I tested by sitting on it.

Mark B

unterhausen

The welding of those barrels was impressively bad. Properly brazed barrels aren't going to come off. I'm not so sure that internal ones are better, and there is no need.
I don't like rivnuts. The lbs is always drilling them out because they let loose.

prairiepedaler

It would've been nice if they had been properly attached. I guess the guy who did it in the factory had a weld quota to meet that day.

unterhausen

I will never weld one but brazing them properly does take some time, at least for me. I can see why they would want to rush it.

prairiepedaler

For the unwashed like myself, I just use "welded" as a term. The P-clips currently in use are doing their job, but they aren't the most elegant solution. I think in the future I'll just use P-clips on a frame when barrels mounts are back there. Hey Unter, have you got any photos of the frames you've made?

unterhausen

It looks like it was welded to me. Two tack welds each. They are hoping you never use them maybe.