# Temperature Control?



## rake60 (Feb 11, 2008)

We all know that metals expand when hot and contract when cold.

If you finish a cylinder bore while the material is hot to the perfect mic reading
it will most likely be too tight once it cools to room temperature.

Print spec sizes are based on 68 Degrees Fahrenheit (20 Celsius) or (293 Kelvin for 
the purist's amongst us )

It can be amazing how little or how much that can come into play.
Today it was a little chilly here. It did warm up to a +15F by afternoon.
Right on Que the roll up door malfunctioned and stuck open in my area of the shop.
The maintenance department fixed the door and got it to close in about 20 minutes.
The parts I was making at the time had a 10.048" bore with a .002" tolerance.
I mic the bore of the 14Th piece and it's .001" oversize. Or NOT!
Rechecked the mic to the standard and the Mic had shrunk .002" from getting that 
cold. It checked +.002 to the standard.

Temperature not only effects the work piece.
It also effects the measuring device.....

Rick


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## wareagle (Feb 11, 2008)

rake60  said:
			
		

> Temperature not only effects the work piece.
> It also effects the measuring device.....



And the machinist! 

Great illustration of thermal expansion/contraction. Thanks for sharing!


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## tattoomike68 (Feb 11, 2008)

I think for steel you can figure about .000007" of an inch per degree F.


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