Recently purchased a Bike Friday NWT. Low price due to a broken frame part. It is part that looks like a fork DO. It broke at the base. Most of the loading is axial so I was wondering which approach to use. Brazing would be less of an impact with heat, but maybe it is a non-issue. I could remove the rear triangle and have it cleaned and PC too. If I have it welded, should I chamfer the longitudinal edges for filler?
That is what I would do. Have you contacted BF about a repair, or about getting parts so you don't have to fab them?
Heat of brazing is lower temp than welding, but both are over the trans temp, and in this case the 4130 isn't an issue anyway. The heat (non-)affected zone is large with brass. Though it doesn't mater. BF uses TIG, Brass, and Silver on their bikes in the appropriate situation.
Yes I am in contact with BF. They are reviewing the same pictures.
I don't know if it was brazed or welded in this area. I have access to an expereinced resource for brazing. If I can get the part from BF that is what I will do. They have improved support in that area and may offer addtional solution.
I live in the DC area and am not inclined to send the part to Eugene OR for repair when I can do it locally. It is a non-critical part that is not challenging to repair, like a broken RD hanger DO.
Live Wire: The failure is not in the joint but the part. I suspect it is a lazer cut part unique BF PN (Part Number) on the BOM (bill of material).
Live Wire: OK got it! The joint is too close to the failure and any heat of welding would melt the brazed and the part would fall out! Went right by me. I know there was a reason I posted this in this forum!
I will ask BF for a part and have it done locally.
Yup, replace and rebraze. Welding it is out as it looks like the crack is touching the old brass.
+1 If you get brass in the weld it's shot.
On the other hand, it's already broke. You could try welding it and it it fails again, buy a dropout from BF and braze it back in.
Just remember if/when you're removing the old part, focus the heat on the part and not the tube. I'm not one to fret over HAZ as the best construction method is depended on the craftsman not the torch... but if you cook a tube, that's bad voodoo. -Chris
Ordered parts last Thursday and got them today! The part was $2.24. Lazer cut locally I am sure. Also ordered the Caprio removal tool, also lazer cut.
The person doing the brazing just built his first frame. Looks pretty good for a first one. He is about to start on his second. I appreciate the tip, Dornbox. It makes good sense since most of the mass is in the part, not the tube.
I don't think a competent welder would attempt a weld that close to brazing. As mentioned above, the weld would fail quickly and the welder would get sprayed with molten brass. Win-win
Tell the guy doing the repair to mostly heat the broken part, he probably can get it to fall out if he has a weight on it. The small part in the tube will be harder to get out. It might help to do some drilling
Who provided the parts? I could use some BF parts if someone is making something similar. The rear drops that attach to bends are a pretty standard part, though I don't know who makes them, and the "drops" that attach to the seat posts would be useful.
SJX426 - Have to guess that the bike is out of warrantee (OOW) coverage; otherwise the factory should send you a replacment fork to swap out and ask you to send the old one back for examining. On the sidebar, looking at picture #2, I must contribute that imho the design looks poor from the start. Looks like it was just meant to break off the dropout just as it happened. Unless it is not feasible for some reason, I would suggest buying or fabbing a set of the "plug type" front dropouts that would slide into the end of the round stay / blade ends and would better distribute the forces. Thoughts on that idea?
Yes it is at the end of the seat stay of the rear triangle. I have removed the paint via wire brush exposing the brazed area. I also drilled out as much as I could without compromising the tube wall. Here is the "Drop Out". It appears that it is located against one side of the tube with braze filling the remainder portion of the opening. I believe it is also bent to allow for proper alignment with the QR. DOs.jpg
Or the other option is the bridge between the two. The disadvantage would be that it would be fixed and any displacement from the clamping forces would induce stress at the bridge joint. Should round the edges of the part too to provide stress relief.