'94 explosif

[Err]

Yeah, that's a last resort though, and as you say at a temp well below that needed to melt alu, i would imagine. With alu post in steel you'd be better with chemical destruction, although that's pretty drastic too.

 

[one-eyed_jim]

Has anyone seriously tried to melt out am Alu seatpost from a Steel frame? That's seriously one of the most idiotic things i've ever heard.

I haven't done it. I've had it done, I've seen it done often, and I've seen the frames so treated live long, happy lives with new paint.

Here, you can go tell Dave Moulton he's an idiot:

http://davesbikeblog.squarespace.com/

It's not simply a matter fo the relative melting points: one must also consider the effect on the heat treat of the steel. You're making one huge Heat Affected Zone.

Time is also an important factor in heat treatment. Most bicycle steels aren't heat treated, and the time and temperature involved in melting out a post isn't enough to anneal steel. If this were a problem, fillet brazing - which requires much higher temperatures and generally takes longer - wouldn't be possible. 600°C for five or ten minutes simply isn't a problem.

 

[one-eyed_jim]

Delicate heat-treated tubes like Reynolds 753 are silver-brazed at temperatures around 600-700°C

That is around and about the temperatures needed for melting Aluminiun, depending on the alloy.

I think that if you read up the thread a little way you'll see that I made that point already. To spell it out, famously delicate steel tubes are routinely silver-brazed at temperatures similar to and higher than the melting point of aluminium. Not gas pipe - Reynolds 753.

Really, I don't speak as an 'armchair' mechanic, have had to rectify blunders from others quite a bit in my working life as a motorcycle-mechanic. And these problems/blunders also cover blowtorch malhandlings.

It's possible to destroy a frame with a mishandled blowtorch - that's clear. It's also possible to destroy a frame with a mishandled hacksaw, a dynafile, a lathe, a drill, or simply by clamping it clumsily and twisting hard. There are as many ways to screw up as there are to do the job properly.

 

[Err]

Why is it preferable to chemical dissolving?

 

[one-eyed_jim]

Why is it preferable to chemical dissolving?

It may not be, depending on circumstances, but it's not always easy to get the ammonia where it's needed. The corrosion products expand to fill the interface between the post and the frame. Ammonia needs to penetrate that layer to react with the aluminium oxides and dissolve them out, and that can take a long time. Melting is quick, and just about certain to succeed. Obviously it makes sense to try other methods first if the paint's worth saving.

Just to reiterate, I'm not saying other methods don't work. I'm only saying that melting does.

 

[Drapoon]

I sawed a stuck steel seatpost out of an aluminum Kona Koa.

I sawed the seatpost to a stub then used a close quarter hacksaw (about £2 from Wilkinsons) took me about 2 hours over the space of a few days)

my oh my the pain was worth it when I yanked the bloody hunk of crap out of the frame ;-)

 

[one-eyed_jim]

I sawed a stuck steel seatpost out of an aluminum Kona Koa.

See, that's where you went wrong. You should've melted the frame off and kept the post...