Butchering an old Pompino into a shiny fixed/front disk winter commuter

i think the only way to avoid fucking the paint when using caustic would be to have a constant cold water stream on the outside of the frame while the caustic ate away at the post from the inside...

Not fused about paint. I'm going for caustic. A hacksaw blade only just reaches towards the bottom of the post and even with a torch, I can't see how well my cutting is going lower down the shaft.

I've cleared some space in the shed so I can apply the potion outside, wait for it to settle down and then lock it in the shed out of the way while it bubbles slowly away all day. Then, in the evening when home from work, reapply as many times as possible before bed, where it can again soak overnight.

Hopefully, given a few days of this process I'll be somewhere close. Will try to pull/chip bits away once some of the material has left. As I've prised the top part of the post away from the tube, I'm hoping it can get down the inside an eat some of the galvanic corrosion that is causing the problem. May be wishful thinking.

sounds almost exactly the same as mine!
be sure to wear gloves / goggles / take pics!
i've emailed a local metalworkers this morning to see if they are willing to lathe mine out.

Do you need a fork? I have a steel disc fork from Planet X, a Pompino I think

I have a fork in mind already thanks.

If it's steel and on-one its probably the pompetamine fork. Sure it would be snapped up if advertised in the Pompino thread.

Bubbling has started....

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That's pretty wild. So the caustic soda melts the post away and not the frame as it's Alu?

I thought it melted all but steel? I had to use caustic on the wifes bike to get the seatpost out, frame was 531 so survived, the alu post though came out wafer thin once it finally released.

Yep, caustic eats alu but not steel. Do not do this in an alu frame!

nice! what ratio caustic / water did you use?
i take it you bunged up the inside of the tube somehow?
the fabricator i spoke to about removing my post said they'd heat the tube to get it out, thus wrecking the paint, so going to see if any other local companies can do it on a lathe...

In terms of ratio - I'm not sure....I put some cold water in old plastic bottle. Then shook some granules in, aiming for around 5 parts water to 1 parts soda. Give it a shake, it gets hot in the bottle. After about 30 seconds shaking and the bottle starting to shrink, pour it into the top of the post slowly, standing back as the bubbles spit out. You have a bit of time between pouring and bubbling. Wore some big sunglasses and thick rubber gardening gloves.

At the moment, its 100% more fun than the hacksaw. I have no idea how long it's going to take though. I did a few fills an hour apart last night, then left it soaking till morning, did another fill, let it die down a bit before leaving to soak all day in the shed. If it's close by the end of weekend I'll be happy.

Plugged the bottom of the seat tube with blue tack via the BB shell. Seems to be holding remarkably well.

Also, I heard heating is a no go with alu on steel. Alu expands more than steel, so it gets tighter. You want to freeze it, as alu will contract more. Some folks mentioned using a CO2 canister, or dry ice, to shock freeze the post so it breaks the galvanic weld.

yeah, i guess they were on about heating the frame, hence ruining the paint. it's a no-go anyway.
good luck with the caustic, keep us 'posted' #dadjokes

Excellent. Love the gif.

Praise the lord for 2 Al + 2 NaOH + 2 H2O → 2 NaAlO2 + 3 H2

The post is out. Can't quite believe how quick and easy it was. Started Wednesday evening, all done by Friday morning and used maybe 500g of caustic via 5 or 6 refills over that time. Paint seems (frustratingly) to have survived too.

The only thing left is two slithers and a random flake of post.

Happy Dayz

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Incredible. Well done!

I heard heating is a no go with alu on steel. Alu expands more than steel, so it gets tighter.

I watched a youtube video once that claimed this was a bit of a myth.

Yes ali does expand more but where its expansion is restricted it can expand in the other direction so instead of getting wider it'll get longer.

The best bit is that when it cools and contracts, it does so regardless of which direction it was able to expand in so it will pull away from the sides and loosen.

The example being demonstrated was an ali fastener in a block of steel so I don't know if a seat tube would restrict the expansion the same or not.

For the info anyone reading this with a stuck post, the best thing to do with a hacksaw blade is to get a bit of dowel that's longer than the blade. You use the hacksaw blade to cut a slot along the length of the dowel then flip the blade around and glue it into the slot, teeth facing out, with araldite or the likes. Once the glue sets you'll be able to use the full length of the hacksaw blade, holding the dowel is more comfortable than holding the blade and the dowel stiffens the blade too.

There was a guy on retrobike making a version of this from steel bar and it had set screws so you could replace the blade but I think it was a while ago.

Hmmm, interesting.

This is a good shout. One of the issues I had was the blade would flex. Still, I got there in the end....

Can you/anyone recommend a good paint stripper/technique.

The frame is covered in chips/rusty spots, and I'm going to grind off the canti studs and cable guides, so was hoping to take it back to bare metal so I start with consistent surface.

I've been blowtorching and wire brushing to remove paint recently but that's been on forks and components, a full frame would be a bit tiresome.

Nitromors is shit now. Think there is a 'trade' version that's as potent as Nitromors used to be but not sure what its called or how easy it is to get hold of.

Yeah, been looking at this stuff from ebay:

Do I need a good face mask or will I be OK if out in the open and don't actively try and breath it in?

I understand the reason old Nitromors and the like were banned was connected to people dying. I'm trying to avoid that on this build.

Do I need a good face mask or will I be OK if out in the open and don't actively try and breath it in?

https://www.maxolen.co.uk/images/maxolenuk/dichloromethane.pdf

Hmmm, I've used old Nitromors inside the garage and didn't die. Though I do have "exercised induced asthma" nowadays.

Get a mask and do it outside.

Do you really want to fuck about with banned
carcinogenic chemicals bought off eBay, described in Comic Sans, with (I'm guessing) inadequate safety equipment, and no training in appropriate handling?

It would probably be fine but is it really worth the risk when a bit of elbow grease with the safe stuff or £20 (or so) to a local shot blast person would get the job done?