Theodore Heise considered Tue, 10 Jan 2017 20:00:09
+0000 (UTC) the perfect time to write:

On Mon, 09 Jan 2017 22:20:13 -0800,
Jeff Liebermann wrote:
On Mon, 9 Jan 2017 22:24:41 -0000, "Benderthe.evilrobot"
wrote:

"Theodore Heise" wrote in message
...
On Sun, 08 Jan 2017 17:01:01 -0800,
Jeff Liebermann wrote:
On Sun, 08 Jan 2017 16:31:15 -0800, Jeff Liebermann
wrote:
(...)

Yet another untested idea...

Use an induction heater on the steel cup.
https://www.youtube.com/watch?v=MyZEaPQinO0
https://www.youtube.com/watch?v=YJElT9xK3bk
https://www.youtube.com/watch?v=uimEZKrVNO0
https://www.youtube.com/watch?v=3u1IBgefNDs [1]
http://www.theinductor.com
You'll need various size coils for different bolts, cups, seat posts,
etc. There are induction heater kits on eBay:
http://www.ebay.com/itm/1000W-ZVS-Low-Voltage-Induction-Heating-Board-Module-Flyback-Heater-Brass-Coil-/282317713643
The steel cup gets hot and not so much the rest of the bicycle,
including the aluminum bottom bracket which sucks away much of the
heat. However, you can get the steel hot enough to melt the aluminum,
so please use an IR thermometer to keep the temperatures down.
Aluminum melts at 660C.

Yikes!

Is there a problem?

Maybe, maybe not. I read "induction heater" and just assumed it
would be pretty complex, and possibly dangerous (to me and/or
bike). Maybe I goofed by not reading the links.


An electric heat gun is safer than a blowtorch - but I think
you still have to be a bit careful.

The heavy duty paint strippers aren't too bad, but some heat
guns are designed for lighting solid fuel cooking ranges.

The problem with external heat generators is that the heat
affected zone is rather large and will surely creep into
undesirable areas, such as painted parts.

No painted parts, it's polished aluminum.


...With an induction
heater, you only heat the steel parts. Aluminum only gets hot
as far as what it conducts away from the steel.

If you happen to have an induction cooktop stove, you can
demonstrate how this works. Put a steel pot on top of the
induction heater, and only the steel will get hot. Put an
aluminum, glass, or copper pan on the stovetop, and they stay
cold. Toss a coin with stainless (magnetic stainless mostly
works, non-magnetic does not).

It's the same with using an induction heater on the bottom
bracket. The steel components get hot, while the aluminum
bottom bracket and frame do not.

I don't propose heating the cup to red hot:

http://www.hearth.com/talk/attachments/metal-color-temp-chart-png.100306/
which is why I suggested an IR thermometer be used to monitor
the temperature.

Too much complexity/equipment for me, but thanks for the thoughts.

I'm slightly surprised by the lack of reference so far (at least that
I've seen) to the relative expansion rates of aluminium (the BB shell
and the rest of the frame) and steel (the bearing cup).
As aluminium expands at a much greater rate than steel, simply heating
the whole lot by any significant amount (say by pouring boiling water
over it) should ease the grip of the shell on the cup.
I've done this exact thing on components of many different things,
ranging from fairly complex engines to assorted plumbing!