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  • Mine is aluminium on aluminium so I assume it's worse

    Definitely the worst of all possible worlds. Don't even think about chemistry, you'll either have no effect or you'll destroy the frame first as it has the thinner walls.

    The seat post is toast if you want to save the frame. Depending on how far gone it is, the frame might be toast too. What you need to do is machine away the seat post from the inside out. The "big machine" method is a horizontal boring mill. Since the seat post is round and straight, it would be a fairly easy set up to get the frame on the table with the seat post coaxial with the spindle, the main caveat being to remind the machinist just how thin the wall of the tube is before he puts too much gronk on the workholding solution. Once you have it held in the right place relative to the tool, it's just a matter of taking light cuts with a boring bar until the hole is the same diameter as the seat post was. If you're left with a shiny bare metal bore, you've won. If there's still a fair bit of powdery crap in the bore before you break through to actual seat tube metal, you've just wasted your time 🙂

  • Yeah hold on, let me go the garage and start the machine right up!!

    Looking at the condition of the rest of the frame i recon its in for good. Im going to try some chemicals first as this frame owes me nothing and its worth a shot.

  • its worth a shot.

    It’s really not. Buy some plusgas or other penetrating fluid and soak it repeatedly from the inside, upside down.
    Trying to melt it out with caustic soda is a dead certain frame ender.

  • Im going to try some chemicals first

    I still wouldn't.

    While an HBM is the optimal time saving tool, tester's law of subtractive manufacture says you can achieve the same result with hand tools and sufficient time.

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