[Closed] Has anyone ever really removed a seat post with caustic soda?

Is it an aluminium post in a steel frame?

Presume it's an alu post in a steel frame? It takes a LONG time.
Take out everything inc bottle boss bolts. Mount frame upside down, pour in conc NaOH from the BB shell. Leave overnight.

Pour it out in the morning, replace.

Probably take 3 or 4 goes. I probably don't need to tell you to wear gloves and goggles when handling it do I? Once the seatpost is out, flush the frame out with lots of water.

Sounding like buying a used frame might be a better bet 🙁

I did one in a DMR frame a few months back. It did take a long time. I plugged the seat-tube at the bottom, sat down with my glasses on, and just kept topping it up over several nights. Got there in the end.

Still haven't got around to doing anything with the frame though as it goes...

i wouldn't do this, caustic eats aluminium i think...

Coca cola freed my mates Thomson out of his soul frame

Is it a carbon post?

The best way is a hacksaw and cut it but like you say at 400 that's going to take sometime.

Have you tried turning it upside down and hitting it onto a block of wood? Use the weight of the bike?

If that doesnt work leave it upside down and tie a weight to the post and keep squirting wd40 down the tube from the bottom bracket.

Then keep giving it a go at and see if it moves?

Good luck

caustic soda worked for me (obviously alu post in steel frame) when nothing else did. If I was doing it again I would definitely wear glasses as it was a pretty violent reaction when it came free!

+ 1 for coke...

Left it over night and it finally did the trick

Managed to get an aluminium post out by cutting it off flush at the top of the frame, cutting down as far as i could inside with a hacksaw blade and then chiselling it out piecemeal, breaking off chunks with a chisel and then a large (OLD) screwdriver. Took good couple of hours, but worked a treat with minimal damage to the frame. It cracked the paint so probably not recommended if you are considering selling the frame on.

probably a last resort!

For the record, it's an Alu post (well, it was, now it's a mangled mess).

Yep, also had success with this (again stating the obvious - alu post in steel frame).
Took about five nights with about 3 or 4 top ups of caustic, did it outside and if i'd been a little more careful could of got away without having to respray.
If OP is not having any luck, perhaps stronger caustic...just don't breath it in..

Use ammonia if you can find some http://www.sheldonbrown.com/stuck-seatposts.html

Why does the NaOH eat away at the aluminium but not the steel?

talk to a frame builder about getting it reamed out?

Also, not sure on frame value but have you tried heating it up with a blow lamp. I guess the top is off the post from what you've said so getting purchase on the post itself might be an issue to twist when it's all heated up but you could try and expanding bung type thing in the top. Obviously a respray might be required afterwards!

Just before Christmas I removed about 5" of seat post from the bottom of the ST.

The original owner had gotten the post stuck, cut it off where it stuck out and hammered the rest in!

I used caustic soda. Mine took about three hours leaving each solution in for 15 - 20 minutes using a progressively stronger solution.

Lots of heat (caused by the reaction), nasty fumes but perfectly straight forward.

I was amazed by how much of the post was "eaten".

I was able to remove what was left with a piece of copper pipe run through the remaining seat post hooking the bottom.

I was always planning a repaint, but I would guess if you were careful the paintwork could be saved.