bark_eater 

I brought home another basketcase, this time a Schwinn Passage.
I knew it had some major problems, but I was only after the frame. When I started cleaning it up I found this dent in the back of the fork blade. It looks like some one pinched clay and left a mark with their thumbnail.
I have a fork from a similar vintage touring bike I can use, but I was wondering If this fork really needs to be condemned, and if there where any guesses as to what left this kind of mark.

I cant get a good closeup with my phone and I was edge lighting the dent with a flashlight, so this is worse than it looks in person. The opposite rust patch is part of the "pinch" and the blade has been left slightly narrower.


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Andrew R Stewart 

I guess a steel fork blade failure mode would be slow enough, due to this type of stress riser and cross section shape deformation, that someone who was clued in could monitor daily to avoid the worst case scenario. Will this fork be used by said person? Andy

bark_eater 

Its not something I would pass along to another rider. At first I thought it was damage from a cutting disk, from someone cutting a chain, but then I saw the pinch. I think it will end up in the destructive testing pile. I have wondered if filling defects like this with brass has any effect on a stress riser like this.

unterhausen

I couldn't make myself ride that. That's just the way I am.
My criteria is if I know for sure there is no reason to suspect it would break. In this case I couldn't say that.

guy153

As for theories about how it happened, maybe there was a light bracket or something on there with a poorly-designed clip that was very enthusiastically tightened by somebody. If it was on the frame nothing to worry about but caution is warranted when it comes to forks. Would probably be OK but would you want to take that risk? I think these Schwinns are just mild steel so could easily be repaired.

bark_eater 

Its a Hi-Ten fork. Did you have anything specific in mind as far as possible repairs?

guy153

Hi-Ten is basically mild steel, so you could just weld it-- you can weld Cromoly obviously as well but you have to think about heat cycles and things a bit more, and because it's thinner you really want to use a TIG. This fork is probably thick enough you could just buzz it with a MIG-- obviously clean the area up first.

bark_eater 

That's interesting. So physically filling the dent with a weld, and the heat penetration, would improve the structural integrity? That's interesting idea, as if the dent/notch was filled, the slight flattening of the fork blade would be very hard to see under paint. the idea of an "invisible repair" is tempting, but feels a little sketchy at the same time.

guy153

The heat wouldn't do anything special-- mild steel is basically the same before and after you weld it. But if you're adding metal you're adding strength. So yes if you just filled it all in and sanded it smooth I don't think you would have anything to worry about.

bark_eater 

I pulled the fork and its a Tange "51" . That makes me feel better about the idea of replacing it, as it was not "made in the USA" like the Tenex frame.

I will give the mig welding a try though. There is a local "wizard" class welder and I can add this to the collection of small repairs I need to take over.

CliffordK

TIG welding?

unterhausen

Yes, OP would want it to be TIG welded

bark_eater 

Tig welding. Noted, thanks.

guy153

TIG is always better. My point was just on this fork you could get away with MIG (or even flux core) if it was all you had.

bark_eater 

Understood.. This came to mind thinking on this:

Vigor's Black Box Theory