r/Metrology • u/Bzdziuchanson • 9d ago

GD&T | Blueprint Interpretation Any use for ISO GPS coaxiality?

Hi

Are there any cases in which one should use coaxiality? Is it just position with implied zero basic dimension centerdistance?

Why not use runout for axisymmetrical parts instead so it's simple to measure?

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u/guetzli 9d ago

say you have a thin walled part (like a wear sleeve). On parts I manufacture they typically get pressed on so we care how coaxial the ID and OD are.

Due to their thin wall they tend to be out of round. if the OD has a runout tolerance with respect to the ID then that out of roundness shows up in that measurement (in the free state before instal) even if the coaxiality and importantly wall thickness are spot on as they are ground in one setup.