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I went to tighten up my rear rack and realized that it was actually a screw not a bolt holding one of the arms on my rear bike to my frame. Apparently I stupidly used a screw that's longer than the width of the post to replace a bolt that had fallen out a while back. The tip of the screw is poking out the other side of the tube. The head of the screw went in a pre-made hole on the frame, but the tip is now poking out the other side. Doesn't look good, can it be repaired? enter image description here

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    Is that a self tapping screw? I'm wondering because I don't remember any other type of screw having a pointed tip. Self tappers are not used on bikes as far as I can remember. Maybe for holding cheap reflectors on the rack, but not for load bearing parts. If it is a self tapping one, you most likely also ruined the thread of the hole.
    – Arsenal
    Commented Jun 10 at 12:35
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    Have you changed to the correct threadded bolt? Or do you wish to keep using the screw?
    – Criggie
    Commented Jun 10 at 22:54

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Can it be repaired? No. In general, an Aluminium frame shouldn't be welded after the initial manufacture due to the risk of local cracking and embrittlement. Factory frames are heat treated post welding to recover ductility and homogenise the metal structure.

On the plus side it’s a relatively small hole that will be even and cone shaped on the inside and will be less likely to act as a stress riser. Plenty of frames have small gas exit holes by design.

The hole is also inside the baby triangle made by the bridge which should provide enough extra support.

Lightly file down the lumpy exit hole on the outside to make it clean and not sharp. If the hole seems particularly jaggy after sanding you might wish to drill it out with the minimum size drill bit possible (2mm ?) from the mount side. My instinct would be to leave it alone after filing on the basis of don't break it more.

It’s not an ideal situation but keep an eye on it and regularly check for cracks, tearing or folding.

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    I'd be tempted to say drill it out, as the current hole may be star shaped and/or have points. If it was DH MTB rig, I'd call it a write off. But a commuter.... I'd never tell anyone it's fine to risk it. But I'd happily risk it. :-D Commented Jun 10 at 13:42
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    "An Aluminium frame can’t be welded after the initial manufacture." Obviously, someone with an aluminum welding rig can attempt to do it. So what's the underlying reason? Factory welding is followed by some processing steps (annealing or something) to secure the weld that can't be replicated in a shop environment? The alloys used are not compatible with typical aluminum welding equipment? Something else? Commented Jun 10 at 14:09
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    @WaterMolecule One may weld an aluminum frame with a TIG rig but AFAIK it destroys the heat treating done after frame manufacture. I think the frame is dumped into a big oven and left to bake for a while. vitalmtb.com/forums/The-Hub,2/… Commented Jun 10 at 14:55
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    @GrimmTheOpiner I was tempted to say to drill it clean & round but it's in the realm of not breaking things any further and it would be tricky to get a drill in there. Commented Jun 10 at 14:59
  • Interesting reading machinemfg.com/heat-treatment-processes-for-aluminum Commented Jun 10 at 20:58

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