Stuck Seat Post Removal - Caustic

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  • Hey All,

    Thought I'd add this on here for all of you to see, but mainly for those of you with restorations in mind. I found a good little link whilst searching for some information on Williams cranks. Tells you how to get out a seatpost using the caustic method - dissolving. I got the frame from Bracestower - it's an old Ken Ryall with nice Nervex lugs etc, see previous pics posted somewhere on here. The seat post was well and truly stuck and a rescue attempt had ended in disaster for Bracestower - you can ask him what happened.

    Just got the first dose of caustic going. Here's the link to the site for instructions:

    Dissolving method

    I've decided on a just over 5N solution of caustic. I'll add on here as it goes so people know how long to expect to wait for it to have all dissolved.

  • .

  • Sorry eyebrows - I just got the N from the website - haven't a clue what it actually stands for!!

  • idiotic ramblings of a tired biochemist deleted.

  • Why were you being a dick - you were just being right!

  • Pretty much what i did with my seized post... Took about the same time too.

  • I think the whole thing is wrong - I used 55g of caustic soda to 250ml water

  • -

  • I'm intrigued to see how this goes. It's a lovely frame which I was quite depressed about, but I'm over it now...

    Looking forward to seeing it built up some day.

  • Not long now. Think it's going to get built up, used for a bit while I sort out the Pug, then stripped and resprayed. I've decided to keep the Williams cottered crank for now but I shall put some new pins in to stop any risk of wobble.

  • eyebrows I think its 5M you mean,
    Sorry for being irritating, but in the middle of interviews for lab placements

    N stands for Normal it's a very common way to express the strength of acids and alkalis.
    See: http://en.wikipedia.org/wiki/Concentrati­on#Normality

    Sorry to be irritating, I'm a lab manager!

    Anyway, did it work?

    I tried freezing a seatpost out with liquid nitrogen - tip - it's a good way to crack a frame!

  • AlexB

    Anyway, did it work?

    I tried freezing a seatpost out with liquid nitrogen - tip - it's a good way to crack a frame!

    It's working as we speak. Slowly bubbling away. I'll rinse and see how it is tomorrow and post back.

  • in deference See: http://en.wikipedia.org/wiki/Concentrati­on#Normality

    Sorry to be irritating, I'm a lab manager!

    I tried freezing a seatpost out with liquid nitrogen - tip - it's a good way to crack a frame![/quote]

    Oh well, I only deal in the uM and below range, and never in N.
    guess I was wrong....

  • Molarity is grams (mass) dissolved in volume

    Normality is grams equivalent (taking into account the ionic properties) and dissolve in volume

    ah it makes sense now.

    Although in this case it doesn't matter as N=M.

  • Attention Chemists: I have a stuck seatpost, and am thinking about this method. However, I'm a bit scared of the possible effects of the caustic soda on Columbus SLX New tubing. It's steel but it's very thin. Would steel hardly dissolve at all or do I have to take care to minimise steel-caustic solution contact?

  • Just pour half a bottle of the stuff (i always find it in powder) up your seat tube and add water. Let sit for as long as needed, it won't harm steel. It will harm aluminum, paint, flesh and just about anything else though.

    I had an ahead adapter stuck in some forks, it took a few days but the above method* dissolved nearly the whole chunk of aluminum.

    Still using the forks...

    *sub steerer tube for seat tube, obviously.

  • eyebrows Molarity is grams (mass) dissolved in volume

    Normality is grams equivalent (taking into account the ionic properties) and dissolve in volume

    ah it makes sense now.

    Although in this case it doesn't matter as N=M.

    Incidentally on that link, his '6N' solution, which you'd expect to be 6M is only 5M.
    Confusing, eh?

  • trampsparadise Just pour half a bottle of the stuff (i always find it in powder) up your seat tube and add water. Let sit for as long as needed, it won't harm steel. It will harm aluminum, paint, flesh and just about anything

    This is right - the bottles usually tell you what concentration to use for stripping paint and unblocking drains, but it's fine on steel. Use hot water if you want to speed things up.

    One interesting thing i found out while doing my dissolving is that the bubbles are hydrogen gas, so it's a good idea to do this in a well ventilated place and if you do it inside be aware that a pocket of (explosive) hydrogen could gather in the highest part of the room. Doubt it would be a huge concern given the amount of aluminium we are dealing with on bikes, but one of the professional chemists might correct me!

  • Just spoken to one of the engineers that we use at work and he has a big adjustable reamer. Does anyone know of a database of standard seatpost sizes?

  • it's likely to be a 27.0 or 27.2. There's a database on Sheldon's site, but I doubt it's that useful. Next common size down is 26.4 (I think).

    http://www.sheldonbrown.com/seatpost-siz­es.html

  • Today's update. Upped the dosage today and got much better results. There ain't much left in the tube for me to get out. It'll be interesting to see what's left tomorrow!

  • Doing this right now.

    It's pretty cool to watch, just don't breath in.

    :)

  • The remnants...

  • This was all that was left after Friday's dose. Rinsed it out this morning. So pretty much 3 days to get out. In the end I was using 110g of Caustic soda and 500mls of water per dose. Didn't fill it up all the way to the top straight away as it tends to bubble over - not an issue if you are going to respray but watch out for it! Good luck to anyone else who's doing this.

  • Got a stuck seat post on a crappy old frame I was gonna build up for some practice before attempting a build with a decent frame. What a cool way to get rid of the damn nuisance thing.

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Stuck Seat Post Removal - Caustic

Posted by Avatar for wolfenger @wolfenger

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