GD&T tolerencing on circularity and conc shaft/cyl 1

[rudragoo]

It has been awhile since I had to figure tolerances and clearances with GD&T and I've forgotten the cylinder/shaft rule.

I have a shaft/cyl combo with circularity at .002 and conc at .002. Can you remind me how to consider this with my MMC. Most are clearing with a good measure but one is only clearing with .001 and I have yet to add the GD&T. It has just been too long and my mind is a blank.

Thanks

 

[PaulJackson]

Neither concentricity nor circularity constrain size! If you are analyzing clearance you might want to consider size!

Paul

 

[rudragoo]

Thanks

I know that MMC does not apply but it has been so long that I don't remember whether they affect my tolerance requirement. I have a .001 shaft and cylinder clearance at MMC- just what I want- I don't remember if I have to take into account the GD&T tolerance. Such as do I have to add .001 to my hole and subtract .001 from my shaft if the GD&T tolerance is .002? Or does it not affect my clearance?

It just has been too long and I don't remember. I am going to search my reference books and my course book to try to find an answer but I wanted to check with people that have been using it recently (like in the last 10 years)

Thanks

 

[PaulJackson]

If your drawing declares that ASME Y14.5 is its standard then the form tolerance size for both the shaft and cylinder must be perfect (zero) at MMC (unless controled otherwise for straightness. Circularity could then only be a refinement of form for any given size.

If your drawing declares that ISO is its standard then the form tolerance size for both the shaft and cylinder must be perfect (zero) at MMC only when modified with (E) "the envelope principle" otherwise the MMC size is constrained by other form tolerances i.e. straightness, circularity, etc.

Concentricity only controls location in both standards although it does so differently in each.

Paul

 

[PaulJackson]

error... where I stated "...form tolerance size for both..." I meant "...form tolerance for both..."
Paul