> Tony Smith wrote:
> 
> > Say your 20cm lump of steel is a roller of some sort, and needs a 
> > shaft put thru it.  How do you get a 1cm rod thru the cylinder, and 
> > have it as a tight fit?
> > 
> > You heat up the cylinder.  
> 
> You heat it up as evenly as possible, the whole cylinder. 
> This is /not/ what I'm talking about. I thought I made that clear.
> 
> > Another example is engine cylinder liners.  You bore out the engine 
> > block, heat it up, and drop the liners in.  Hole getting 
> smaller would 
> > be a bonus, it would reduce piston slap.
> 
> I agree. Another example of what I am /not/ talking of. Is it 
> just me, or do you really not understand that I agree with 
> you on all these examples of yours? 
> 
> Gerhard


I understand what you are saying.

It doesn't matter how you heat up the hole, nor how much mass is surrounding
the hole, it will still expand.  The only caveat is if you heat it enough so
it melts or some other factor is at play.

For interest, I looked up the gun barrel example to see exact why
overheating is a problem.  They all say the hole expands, no matter the
thickness of the barrel.  Hunters prefer lighter barrels because you can
swing them around faster, but heavier barrels perform better.  

Overheating problems include erosion of the barrel, ammo 'cooking off' from
the heat, and more telling, a reduction in range (gas goes past the bullet),
and accuracy as the bullet tumbles after it leaves the barrel.

A gun firing creates the conditions you describe.  If the hole in the barrel
shrank on the first shot, the second shot would jam.  That would make
machines guns a bit impractical.

People fit shafts & bearings every day by just heating up the hole rather
than the entire piece.  How aggressively they doing this depends on the
material.  The hole gets bigger anyway.

Tony

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