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Damaged my cog while taking it off. Is there any possibility of repairing it?

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  • It seems to be a steel cog (although plated?). So, yes you could probably have it repaired. However I suspect it's not worth putting that effort in, and replacing the cog would make more sense. If you search for Miche 15T cog you'll probably have no trouble finding a direct replacement. Commented Aug 26, 2020 at 15:11
  • How did you try to take off that cog? That damage is impossible to produce when you take off the cog in the way it's supposed to be taken off. Which is: 1. Take off the circlip (en.wikipedia.org/wiki/Circlip), and 2. effortlessly slide the sprocket off the axis. I guess you have taken a shortcut around 1, one way or another... Commented Aug 26, 2020 at 19:25
  • Looks to me like the tooth spacing is reduced on one side and lengthened on the other. This would add a pressure point such that one link was taking nearly all the force, at best increase chain wear, and the damaged and weakened tooth taking all the load - probably fatiguing it to failure. Ergo Replace it is the only responsible advice you should get.
    – mattnz
    Commented Aug 27, 2020 at 4:06
  • My money is on a material default in the steel.
    – Carel
    Commented Aug 27, 2020 at 7:34
  • @cared default --> defect ?
    – Criggie
    Commented Aug 27, 2020 at 12:05

2 Answers 2

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Sprockets are wear parts anyway so just replace. Welding would be relatively expensive and I strongly suspect it would damage the heat treatment state of the steel.

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Top preference would be a replacement. These cogs are not expensive.

A second idea - It looks symmetrical, so I'd suggest using a small file to blend any burrs or daggy bits that might catch the chain, and then just flip it over so the "miche" branding is on the opposite side.

That way the wear will be on the back of the curve, and you can get some more life out of it.

If this is on a fixed gear bike where you do skid braking, I'd just replace it.

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    That looks like a structural crack. I would replace it and be done with it. If you are going to try to repair it, it should be welded.
    – Duncan C
    Commented Aug 26, 2020 at 20:32
  • @DuncanC possibly - I thought it was a gouge on both sides from a tool. The point about flipping the cog is that point will be in compression, not tension. If a repair is expected, brazing might be an adequate solution. I doubt soldering would be up to the task.
    – Criggie
    Commented Aug 27, 2020 at 0:48
  • I used the term "welded". Agreed that soldering would not be up to the task. Solder is much too soft for a load-bearing repair.
    – Duncan C
    Commented Aug 27, 2020 at 11:35

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