Any advice about using caustic soda to remove an aluminium seatpost from a steel frame?

bonzo_bananabonzo_banana Posts: 238
edited 22 July in Workshop
I'm trying to do this with minimum liquid so it only destroys a slither of the post to enable it to be removed rather than completely dissolve the post. Just wondered if there is anyone who has done this as most of the videos I've seen show the post getting pretty much completely dissolved. My plan is to have the seattube almost horizontal with seat post slightly dipping down a few degrees and tape the end with a thick plastic bag over it. I only have a small hole in the bottom bracket area to the seat tube and I'm going to cut a plastic pipette at the bulb end to connect a small funnel and tape this to the frame at the required angle. I will be wearing my plastic raincoat backwards, eye protection and plastic gloves and mix the solution in a plastic jug. All outside of course. I'm worried about the pipette melting with the heat and wondered if there was a better option for introducing the solution. Perhaps some sort of steel metal tube no bigger than a straw.

There is absolutely no movement of the seatpost. This seems to be the only way to remove it. The frame is from 1995 and in generally superb condition but the aluminium seatpost has completely chemically reacted in the frame and expanded with a hard aluminium oxide surface I'm sure. I'm keen to use the frame in a build it is one of the last frames manufactured at Raleigh probably within 3 years of the end of manufacturing frames.

My theory is that some people have removed aluminium seat posts by cutting a section of the seat post away from within and then it becomes loose but I'm hoping to have the same effect by just soaking partially at the bottom with a caustic soda/water solution. So in the image below there would only be solution at the bottom along the whole length of the seatpost. This means I'm using less dangerous liquid and the seat post loses its ability to secure itself in the seat tube.

thick-walled-stainless-steel-pipe-500x500.jpg
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Posts

  • mickledore.fymickledore.fy Posts: 400
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.
  • photonic69photonic69 Posts: 885
    Caustic soda is really nasty stuff. I've used it quite a bit around the home. You are likely to strip the paint off your frame before the post dissolves.

    Have your tried Coca-Cola? (Other brands are available). Fill tube repeatedly with this for a few days . The citric acid should dissolve a lot of the corrosion. My dad used coke on a 150 year old Spanish pistol he found buried in mud. Three days later he got the firing pins to move!!
  • imposter2.0imposter2.0 Posts: 10,654
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    Have you actually successfully removed a seatpost using this method yourself? If the post is galvanically coupled inside the seat tube, then I don't think cutting a slot in it is going to make the slightest bit of difference...
  • mickledore.fymickledore.fy Posts: 400
    Yes. I have removed a stuck solid seatpost that way.

    The slot(s) allows the tube to be compressed. Maybe only marginally but enough to get movement. Then just keep going.
    Two slots make it easier because suddenly you have two separate pieces to remove. Problem solved.
  • bonzo_bananabonzo_banana Posts: 238
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.

    Yes I've considered that but the chemical way is a lot lazier and less risk of damaging the frame as I'd likely saw into the seat tube itself.

    I've just had a new idea. Use a slide hammer with a bar weight. I think I have an old bar weight I can make use of with my slide hammer. Seems worth a shot. It should make the impact about 5x more powerful.

    Also I've already bought the caustic soda and don't have a suitable blade. Caustic soda seems the less risky method for the frame but more risky for me. Thanks everyone for the advice.

    553997310.jpg?v=1
  • AlejandrosdogAlejandrosdog Posts: 2,007
    I want to see a you tube video of this :)
  • protoproto Posts: 1,473
    The risk free option would be to send it here:

    http://theseatpostman.com/
  • Do it outside. The hydrogen gas created by the reaction is smelly and dangerous.
  • photonic69photonic69 Posts: 885
    Recon it's all gone horribly wrong for the OP after Caustic Soda accident..................

    ZOMBIE_FLESH-EATERS_09.png
  • wongataawongataa Posts: 773
    Do it outside. The hydrogen gas created by the reaction is smelly and dangerous.
    Hydrogen is dangerous but it doesn't smell of anything.
  • AlejandrosdogAlejandrosdog Posts: 2,007
    wongataa wrote:
    Do it outside. The hydrogen gas created by the reaction is smelly and dangerous.
    Hydrogen is dangerous but it doesn't smell of anything.

    It does when it’s exploded and fried his face. Mmmmmm bacon
  • Harry182Harry182 Posts: 739
    Yes. I have removed a stuck solid seatpost that way.

    The slot(s) allows the tube to be compressed. Maybe only marginally but enough to get movement. Then just keep going.
    Two slots make it easier because suddenly you have two separate pieces to remove. Problem solved.

    +1 to the above method.

    I’ve successfully done the same. Aluminium is much easier to cut through than steel so it’s quick work and, with a but if care, easy to not cut into the seat tube.
    Once I’d cut a slot I rolled/peeled the a bit of seat post away from the seat tube and it basically fell out.

    Seems way less a faff than caustic soda with much less chance of it all going horribly wrong.
  • sam_anonsam_anon Posts: 165
    We need an update!
  • pinnopinno Posts: 37,064
    Soak it in Innotec deblocker for a couple of days. Simples.
    S - The Brazilian beach volleyball team
    W - Wiggle Honda
    "This year will be harder than last year. But that is good news; this year will be easier than next year."
  • gaanrowlgaanrowl Posts: 396
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.


    Recently used this method to remove a thompson Masterpiece :cry: from my Ritchey frame. once the vertical cuts were made i used a thin piece of wood and knocked it in between the frame and seatpost, this split the alloy and it came out easily.
  • wongataa wrote:
    Do it outside. The hydrogen gas created by the reaction is smelly and dangerous.
    Hydrogen is dangerous but it doesn't smell of anything.
    It does when it's a by-product of caustic soda devouring aluminum
  • wongataa wrote:
    Do it outside. The hydrogen gas created by the reaction is smelly and dangerous.
    Hydrogen is dangerous but it doesn't smell of anything.
    It does when it's a by-product of caustic soda devouring aluminum
    https://www.bing.com/videos/search?q=Re ... ORM=VDQVAP
  • philkeeblephilkeeble Posts: 106
    +1 for The Seatpost Man. My stuck seat post is a Campag aero aluminium in a steel frame. There is no circular section extending above the frame so can’t use the cut-slot-and-twist method.

    Phil
    Cheers,
    Phil, in Inverurie
  • mickledore.fymickledore.fy Posts: 400
    Just cut two opposing slots. Then carefully, but forcefully, hit each half. A big hammer and a screwdriver or cold chisel works wonders.
  • MidnightMidnight Posts: 80
    photonic69 wrote:
    Caustic soda is really nasty stuff. I've used it quite a bit around the home. You are likely to strip the paint off your frame before the post dissolves.

    Have your tried Coca-Cola? (Other brands are available). Fill tube repeatedly with this for a few days . The citric acid should dissolve a lot of the corrosion. My dad used coke on a 150 year old Spanish pistol he found buried in mud. Three days later he got the firing pins to move!!


    I use 17p 1l cola from tesco for rust removal, works a treat
  • The RookieThe Rookie Posts: 27,520
    If you read Sheldon Brown he suggests ammonia, much less likely to cause life changing injuries and works really well. It dissolves the aluminium oxide that usually causes the jamming with aluminium components.
  • bonzo_bananabonzo_banana Posts: 238
    I've just got back from the hospital today. No, actually that is probably a future event. I tried the extra weight on the slide hammer and it despite the much greater impact over the standard slide hammer it still would not budge. It feels like in other circumstances that might be sufficient but not here sadly. I will try the chemical approach soon. Just building up the nerve or something.
  • AlejandrosdogAlejandrosdog Posts: 2,007
    Make sure you live stream it and give us plenty of notice :)
  • darkhairedlorddarkhairedlord Posts: 4,554
    Why are you removing it? Apart from now its completely wrecked?
  • darkhairedlorddarkhairedlord Posts: 4,554
    gaanrowl wrote:
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.


    Recently used this method to remove a thompson Masterpiece :cry: from my Ritchey frame. once the vertical cuts were made i used a thin piece of wood and knocked it in between the frame and seatpost, this split the alloy and it came out easily.
    Did it split the frame or the post?
  • bonzo_bananabonzo_banana Posts: 238
    Why are you removing it? Apart from now its completely wrecked?

    I bought the bike off ebay for 99p auction, it's a sort of early hybrid design and want to convert it to a touring bike. It has a high quality freehub based drivetrain and strong 26" wheels and the frame seems absolutely ideal for what I want it's just the saddlepost is stuck and too high for me. Even if they had said the seatpost was stuck I would have bid for it, they did warn it hadn't been used for years but was in generally good condition for its age. It looked like a bike that had seem minimal use but hadn't been stored in ideal conditions. I'm trying to make myself a Thorn 26" wheeled style touring bike on the cheap.
  • darkhairedlorddarkhairedlord Posts: 4,554
    Why are you removing it? Apart from now its completely wrecked?

    I bought the bike off ebay for 99p auction, it's a sort of early hybrid design and want to convert it to a touring bike. It has a high quality freehub based drivetrain and strong 26" wheels and the frame seems absolutely ideal for what I want it's just the saddlepost is stuck and too high for me. Even if they had said the seatpost was stuck I would have bid for it, they did warn it hadn't been used for years but was in generally good condition for its age. It looked like a bike that had seem minimal use but hadn't been stored in ideal conditions. I'm trying to make myself a Thorn 26" wheeled style touring bike on the cheap.
    Nice, pics soon i hope.
  • gaanrowlgaanrowl Posts: 396
    gaanrowl wrote:
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.


    Recently used this method to remove a thompson Masterpiece :cry: from my Ritchey frame. once the vertical cuts were made i used a thin piece of wood and knocked it in between the frame and seatpost, this split the alloy and it came out easily.
    Did it split the frame or the post?

    it split the alloy post
  • darkhairedlorddarkhairedlord Posts: 4,554
    gaanrowl wrote:
    gaanrowl wrote:
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.


    Recently used this method to remove a thompson Masterpiece :cry: from my Ritchey frame. once the vertical cuts were made i used a thin piece of wood and knocked it in between the frame and seatpost, this split the alloy and it came out easily.
    Did it split the frame or the post?

    it split the alloy post
    so not the alloy frame then?
  • AlejandrosdogAlejandrosdog Posts: 2,007
    gaanrowl wrote:
    gaanrowl wrote:
    Cut the seat post across, leaving an inch or so protruding from the top of the seat tube. Then get a hacksaw blade in a holder, or a dirty rag, and keep running that up and down inside the remaining seat post. Keep it parallel to the post/tube and eventually you will cut through the seat post. Then grab hold of the protuding bit with pliers, wrench or vice and the post should twist out.

    No need for all those chemicals and the milennials protective clothing. Won't take any longer than your way. You can always make two opposing cuts and then the two halves of the post can be knocked out. Just takes a bit longer.


    Recently used this method to remove a thompson Masterpiece :cry: from my Ritchey frame. once the vertical cuts were made i used a thin piece of wood and knocked it in between the frame and seatpost, this split the alloy and it came out easily.
    Did it split the frame or the post?

    it split the alloy post
    so not the alloy frame then?

    thats what i thought might happen
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