[Closed] Caustic vs. stuck aluminium seatpost

Just so we're absolutely sure.

Its a steel frame right?

Last minute check .... It is a steel frame ... you removed everything aluminium ??? (Seriously remove everything... its easy for it to bubble over etc.)

That out of the way .... I did it during the cold snap.  This was possibly not the best time but hey.... this slowed the reaction down and also caused it to crystallise out in the -5 parts of the frame!

Concentration .... has high as you can... once you add to water it heats up ... add more until it stops dissolving... use a STEEL stirrer.... (spoon)

WEAR GLOVES as a minimum.double up is better as any sharp parts easily put a hole in gloves

... preferably coveralls and goggles very highly advised... keep a bottle of weak acid (vinegar) close by just in case and wash off splashes anyway... your likely to get a touch on forearms etc when you take the gloves off...

I used a old inner tube to seal the frame ...I cut the seat post as close to flush as possible and then clamped the inner tube folded over a few times with the frame upside down.  I then used a big syringe (killed the syringe) I used to use for injecting Stans to inject through the BB.

How long ... a few days ... (seriously).... you need to keep emptying and then add more etc. obviously this will depend on how thick the seat post is!  When you drain it it will kill any grass etc. it lands on....

When you finish make sure you get rid ... mine had crystals formed inside and these then started dissolving when it got wet and started leaking onto the frame and parts.

Remember always add caustic to water , if you add the water to caustic you will have a very strong mixture and could cause harm when it starts getting hot and bubbly. Make sure you have water near by when working, also if you get any on your skin neutarlise with vinegar it will hurt like hell but wil stop the caustic eating away at your flesh . Neutralise everything  afterwards with vinegar then lots of water.

Alternatively contact the seatpostman, based in Chorley .

Great bloke  and very good at doing what it says on his tin.

It dissolves aluminium, not oxide. Just pointing that out.

Seatpostman is local and a nice guy.

I've done a couple using adjustable hand reamers. Effective but very slow (3 hours) and physically knackering. In both cases the last slither peeled out easily (not actually stuck to the steel even though post was VERY stuck when whole).

I did one by cutting a slot into it with a long hacksaw blade, and then rolling it in on itself

Thanks,

Its a pompetamine, I was in two minds to cut the frame and save the post 😉 not much desire to spend money and I thought this would be interesting.

Happy with the chemicals, more wanting to reduce the amount of wastage/ experimentation. I figure a saturated solution in the absence of any lab might be a bit frisky. Will try a 50% solution.

Not vinegar, bicarbonate solution to neutralise.

A set of marigolds should be fine, do it in a well ventilated spot as you'll get a good chunk of hydrogen evolving.

Theres been a few threads on other forums about using a slide hammer with excellent results.

Not vinegar, bicarbonate solution to neutralise.

I'm like 99% thats absolute nonsense. But its a long time since first year general science.

Vinegar is an acid so neutraluses alkalu producing a neutral solution (salty)

Bicarbonate is a base in a solution its alkali as is caustic soda.

So basically trying to neutraluse caustic soda with bicatb is onh ever going to dilute the alkali.

In effect trying to sooth a burn under the hot tap?

Why is all this reminding me of Fight Club?

I have taken quite a few out. I am quite happy with it taking days.

Strength of mix. Put 150cc[work out how much you need] of water in a cup and sprinkle a little caustic in the water and swirl it around. I mix it in a paint mixing cup and you can feel the temperature rise. Add more caustic until it gets hot but not to hot. If it gets to hot it's to strong. I did take one out and check the temp as I did it, it was something like 50C was OK. To strong and it boils when it hit the aluminium and squirts out of the frame.
If it gets to hot in the cup put it down, if boils it will burn you.

I remove posts from assembled bikes mostly, I tip them over and pour the caustic in the bottle bolt holes.

Cover anodised alumninium, if it squirts out and hits anodised ali it takes the anodising off. Cover stickers if it runs over a sticker it will take the dye off them.

I add the caustic and you can feel the temp go up as the caustic eats the ali, once the frame has cooled down it's more or less stopped doing anything, drain it and add fresh caustic. I tend to do it a few times in an afternoon and do the same the next afternoon.

Cut off seat posts I do through the bottle holes, I made a rubber bung that I jam in the tube/top of seat post. I prefer cut off post really as it's easier to drain the caustic out. I sometimes drill a drain hole in the post and block it with a jubilee clip over a rubber gasket.

Last post I took out was from a Marin Mount Vision, ali in ali. I used a Cengarette saw and made
half a dozen cuts almost though the post and crumpled it. Took about fifteen minutes.

If the temp doesn't go up when the caustic is on the ali and you bought the caustic from the pound shop don't be cheapskate go and buy proper stuff.

I'd really recommend double gloves...  it doesn't sting immediately - if you don't have a cut it won't sting until its eaten away to the nerves - just itch.  It's easy to nick a glove and get some inside then not notice for 10 minutes...

I figure a saturated solution in the absence of any lab might be a bit frisky. Will try a 50% solution.

Just count on it being frisky .... your not dissolving pure aluminium and can't control lots of variables.  It's strongly exothermic and reaction speed increases ... so better to assume it can boil over, spit in your eyes and come in contact with any alloy parts in proximity.