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Hmmm caustic soda crystals is natriumhydroxide pellets as linked too.
I planned on dumping them in the solution, your solution with the brush is more foolproof.
Catch is though that my gxp cranks have an attached steel axle and as per tester it runs into the pressed cavity between aluminium and steel which is hard to rinse out so just keeps on dissolving the alu from the axle.I can do a middle ground; keep away from axle and do the ends to save myself from sanding the whole thing.
I'll have an experiment at the weekend to see. Many thanks for your comment too
Rodolfo-
caustic soda crystals is natriumhydroxide
ah I did not know that!
It's the method that I've used many times and I haven't completely dissolved a bike part yet...
With the race face cranks I linked to, it was easy since both arms can come away from the axle.I actually have a set of Sram SX mtb cranks that I'm going to remove the anodising from, but these have the drive side arm attached to the axle like yours.
My plan is to leave the anodising on around the axle/crank interface since it wont be visible when installed on the bike.Previously I used a large tupperware box that the crank fits in. I filled it with the caustic soda solution to a depth of about 10mm and sat the whole crank arm in it and used to brush to coat it then rinse and repeat.
I'm going to use the same method for the sram cranks but make sure that none of the solution contacts the axle/arm interface. I think if I'm careful it won't be a problem.
Once the cranks are polished and installed, it won't be visible.fwiw before I ever tried to remove the anodising on anything of value, I practiced on old headset spacers just to get a feel for how quickly the reaction happens.
Good luck!
edit - if I get round to doing my own cranks over the weekend, I'll take some step by step photos
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natriumhydroxide
aka sodium hydroxide/caustic soda/NaOH/lye
TotalShanner
chez_jay
I've removed the anodising from quite a few things over the years.
Most recently these cranks - https://www.lfgss.com/comments/15683861/
I used caustic soda crystals. Start small with a teaspoonful in about 250ml of water, the reaction starts quite quickly. I used a small brush to daub it onto the cranks and let it sit for 30ish seconds, rinse it off and repeat until all the anodising is gone.
Experiment with different strength solutions, I've done it a good few times and feel comfortable using a stronger solution than above that has the anodising run off almost instantly. Obviously you don't want to dissolve any parts, so rinse frequently.
Do it somewhere well ventilated, it gives off some pungent fumes. I usually do it in the kitchen by the open back door.
It's not that scary, just takes a bit of trial and error. If your cranks disappear then you know you've done it wrong.