This weekend, I finally got the bike over to the LBS, for some professional help in getting the bottom bracket off. It's taken me about 3 weeks just to find time to do that, so you can probably imagine why I never got around to removing it myself.
I collected the bike yesterday evening. The burly dude that runs the place was impressed at how much leverage it took to get it off. If HE had trouble, then I would've stood no chance!
Next up: disintegrating the seatpost with caustic soda!
The plan was/is to plug the holes in the seatpost with blutac, wrap a bin liner around the post as a secondary defence, and then pour the caustic soda in through the bottom bracket.
There was a few problems with this:
Bottom bracket hole is a lot smaller than I expected.
No unwanted containers that're capable of getting liquid into the hole without it going everywhere.
Not wanting to do nothing, I fished a plastic tonic water bottle out of the recycling bin, cut the top off, put rubber gloves on, failed to read the caustic soda instructions properly, weighed 100g of caustic soda into the bottle, then filled it with roughly a litre of cold water.
Suddenly warm water.
Suddenly very warm water!!
Turns out the instructions said to add the caustic soda slowly to the water, and not the other way around.
Fortunately, it wasn't hot enough to melt the bottle. I used a couple of axle stands to hold the frame in place over the bottle, but the ground was a bit uneven, and I was worried the cat would get too curious and lose it's nose or something. I decided I'd put up some defences..
I rescued it three or four hours later, before going to bed. In the morning, I could see what the caustic soda had done:
It did a bit more than merely discolouring the paint - it's stripped it off in places! It's certainly done something to the seatpost, although it's hard to say what, exactly.
I'll have a go at it with a file tonight, and see how much has really been dissolved. With any luck, I'll be able to grab a funnel, some piping, and some blutac on the way home from work, and I can do things a bit more sensibly.
edit: The next attempt will also involve a 50/50 mixture, rather than whatever I used (stronger than normal, but not 50/50). I'm hoping I can get it dissolved before Saturday, so I can take it to be powder coated.