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Thread: Weld or braze

  1. #1
    Senior Member SJX426's Avatar
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    Weld or braze

    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?

    What are you thoughts?

    Break on NWT.jpgBreak on NWT Inside.jpg

  2. #2
    Old fart JohnDThompson's Avatar
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    It looks like it was brazed, so you can melt the brass, pull out the broken pieces, and replace with a new dropout.

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    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.

  4. #4
    Framebuilder
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    Yup, replace and rebraze. Welding it is out as it looks like the crack is touching the old brass.

  5. #5
    Senior Member SJX426's Avatar
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    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).

  6. #6
    Framebuilder
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    Quote Originally Posted by SJX426 View Post
    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).
    I know, what I'm saying is that trying to weld the part will end up contaminating the weld with brass because the crack is so close to the join.

    Even if you couldn't get the part from BF, it looks like it would be easy to make.

  7. #7
    Senior Member SJX426's Avatar
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    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.

  8. #8
    Junior Member DORNBOX's Avatar
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    Quote Originally Posted by Live Wire View Post
    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

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    There are tons of guys who can braze stuff together with brass, but you need a bicycle or aircraft competent type person, or a welding geek.

  10. #10
    Senior Member SJX426's Avatar
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    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.

  11. #11
    Randomhead
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    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

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    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.

  13. #13
    Senior Member SJX426's Avatar
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    Bike Friday sold them to me. Call customer service. They are very helpful. They sold me a complete set of decals for less than $8. Head badge was a little expensive, but they have them!

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    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?

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    It`s second hand, so coverage may vary. BF is providing good brand coverage.

  16. #16
    coprolite fietsbob's Avatar
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    Its not a standard fork dropout, but apiece they have made, ..
    much longer tang..

    top of the seatstay .. the QR is to fold under the rear section,
    in the travel packing process..

    but if you have the steel plate, a bench vise,
    a grinder and files and time to spend, much can be done..
    Last edited by fietsbob; 09-21-12 at 01:07 PM.

  17. #17
    Senior Member SJX426's Avatar
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    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

  18. #18
    coprolite fietsbob's Avatar
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    Bene Sugg:might double the tang thickness in the repair,
    right up to where it has to come along side the QR at the top..

    add thickness where it flexed, before.

  19. #19
    Senior Member SJX426's Avatar
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    Hmm... might be a good idea. Just use the part in the tube but extend it up on the inside. Will have to see how much is left in the tube.

  20. #20
    Senior Member SJX426's Avatar
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    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.

  21. #21
    Senior Member SJX426's Avatar
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    Thought I should update this thread. Had the part repaired with a combination of tig and braze as it was from the factory. Assembled this week end after picking up the part from the powder coater.

  22. #22
    Randomhead
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    thanks for following up. Looks great

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