Hot or cold for expansion ?

[robgraham]

I'm making a 50mm long aluminium sleeve for a 12mm steel shaft; it is just a support sleeve, no rotary motion. I've reamed the Al. out to the 12mm required and tried fitting the steel shaft. It went in fine, but I suspect it's picked up a little flake of the Al as I went to withdraw it and has stuck fast.

Do I heat it to assist removal or deep-freeze it ?

The second bush is fine with the same reamer setting, but I made sure there was no debris lying around on the trial fit with an identical bit of steel.

Thanks Rob

[Dave Liquorice]

Google is your friend:

"coefficient of expansion metal*"

First hit:

'll leave the drawing of the answer as a excercise for the OP.

[Graham.]

like aluminium expands twice as much as steel, and as the ally is on the outside, you need to heat it.

[Donwill]

Don't forget that bimetallic corrosion may occur especially in damp/wet conditions, the results may cause the two metals to corrode and seize up.

Don

[dom]

Unless you've got CO2 or N2 freezing gear, you're only going to get a

20 degree difference by cooling.

With boiling water, hot air gun, or a blowtorch - you can easily get much larger temp differences.

[robgraham]

Thanks guys - I'm afraid the quick answer was I just took a biggish punch and drove it out. And yes, there was Al smeared on the steel and had to be file off.

I suppose I should have remembered that Al has the larger Cf of Expansion and just plunged it into some boiling water.

Rob