I asked a friend of mine who does blacksmithing, this was his answer.
If the whole sheet of steel is heated evenly the hole will enlarge.
if just the area around the hole is heated the hole will decrease.
IMHO From my line of thinking it makes sense. but not to sure.
just a thought


Gerhard Fiedler wrote:

>William Couture wrote:
>
>  
>
>>I suggest an experiment:
>>   1) A piece of metal with a hole in it
>>   2) A THIN-WALLED glass "jar" the exact size of the hole in the metal
>>       (a light bulb will do)
>>   3) Appropriate heat source.
>>
>>Put glass "jar" in hole.  Apply heat.
>>
>>See if "jar" breaks.   If it does, the hole has shrunk.
>>
>>If it falls out, the hole has expanded.
>>
>>Let me know how this turns out.
>>    
>>
>
>I might do that if/when I have the required equipment. OTOH, the expansion
>coefficient of glass (9 ppm/K) is close to the one of iron/steel (12
>ppm/K), so this is probably not the best "hole filler". Quartz (<1 ppm/K)
>is probably better (but more difficult to find around the house).
>
>Gerhard
>
>  
>
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