So if the CMM room temp. changes from 70-80 degrees, would that mean that 15.000" dia would actually grow up to .001" ??? Yet the result would still be 15.000 ????
Our CMM area and manufacturing area are always 68°±2° and less than 50% RH. With the tolerances we hold, we wouldn't have a change in an unstable environment
Dan, I am not sure I fully understand how the temp. Effects the measurments. So using my example of 15.000” diameter where the temp of a cmm room is 80 degrees using the coefficient of 6.5. Means that the part can grow up to .001.. so when the part is measured on the CMM and result is 15.001 what does it mean?
The way I was tought is that if the part and the gage expand at the same rate, then the readings would not be effected.
When cmm is being used, does this still applies? Can you explain this?
Well if your part and your gage are made of exactly the same material, at exactly the same thickness, receiving the exact same deviations in temperature, maybe.
Otherwise, any measurement that gets taken from the expanding diameter will be different. It's
typically minuscule, but if you work in tight tolerances you might want to do some studies/tests.
For example, our tolerance on an OD could be 50 millionths of an inch, so expansion of .001" is kind of a big deal
Sorry, I was out the past few days because my back decided it was time to remind me that my body is much older than my brain thinks I am.
As mentioned above, the thermal coefficient (more properly known as linear "Coefficient of Thermal Expansion" or CTE), applies in a single direction/axis. So, over a given distance, there is X amount of change (where X is the CTE).
CTE tells you how much change you will see per inch of length, and per degree of temperature change.
So, 6.5 uin/in/F tells you that each inch of length will change by 6.5 micro inches for every degree of change.
If you have a 1 inch length, and change it by 1 degree, then it will change 6.5 micro inches (.0000065").
If you have 10 inch length, and change it by 1 degree, then it will change 6.5 x 10= 65 micro inches (.000065").
If you have 10 inch length, and change it by 10 degrees, then it will change 6.5x10x10= 650 micro inches (.000650")
That is correct. 1 degree F is not equal to 1 degree C. The CTE is different depending on the units. You are more likely to see either in/in/F or m/m/C, but in/in/C does appear occasionally.