[TowerTalk] Metal Thermal Rate of Expansion

[Grant Saviers]

Expansion in an isotropic media such as most metals is the same in all 
directions.  Think of enlarging something for printing by a fraction of 
a percent.

Everything gets larger by the coefficient of expansion/deg C.  Thus, 
holes get larger, OD's get larger, and circumference the same as 
Diameter * pi.  A shrink fit only needs to consider the radial 
interference that is desired.

The 0.00034" change in the radial gap I calculated for 100 deg C 
temperature change is meaningless if the two parts were slipped together 
by hand.  It doesn't matter in this case whether the inside part has a 
higher coefficient of expansion or not, since the gap machined as was 
described was certainly several thousandth of an inch.

Extruded tubing is not round and welded pipe/tubing is even more out of 
round, which is probably why the machining was needed.

Grant KZ1W

On 10/4/2021 11:21, David Gilbert wrote:
> 
> I'm not sure that percentage of expansion is the relevant consideration 
> here.  I would think that the gap between the cylinders (i.e., portion 
> of the diameter) is the important part, and since the expansion occurs 
> in the circumference the gap changes by a factor of pi less.
> 
> Even less reason to be concerned, I think.
> 
> 73,
> Dave   AB7E
> 
> 
> 
> On 10/4/2021 8:00 AM, Lux, Jim wrote:
>>
>> Circumference and diameter grow by the same percentage (since C = d * 
>> pi), so CTE wise, it's the same whether you use diameter or 
>> circumference.
>>
> 
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