Up concerning the caustic soda technic!
Hi to all!
A little UP for this old thread.
I have pretty much the same problem of having some remainings of an old seatpost (alloy) stuck into a frame (steel).
I tried pretty much everything before I eventually decided to saw the seatpost out, according to Sheldon's technic.
Unfortunately, I only managed to get little pieces out.... but the main part of the seatpost still remains in the frame

and it's actually getting harder and harder to saw anything of the seatpost without touching the frame...
I would really like to try to caustic soda technic, to see if this can help....
But I am wondering how to proceed...?
because there is still a bottom bracket in the frame. This one is a least doing its job very fine. But I couldn't manage to open it either without starting to damage the lockring... So I would really like to leave it on the frame.
What do you suggest me to do?
I could hang the frame upside down and insert the caustic soda through the holes of the bottle cage, but then what?
I believe that it won't do the trick magically in a minute....
So how could I leave it long enough for the magic to operate?
I have hard time to see how to proceed. Please help me out if you can!
PS: my current situation looks pretty much like the one seen in the picture on the first post.