Circularity - The Tolerance Zone

There can be a lot of confusion when dealing with circularity - especially when identifying the tolerance zone compared to how Rule #1 controls it. In this video, we provide a visual example to review how rule #1 controls circularity within the area between two concentric circles.
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[@jamalmohd720]

Please GD&T Total course videos upload

[@eartheartbaratheon791]

Isn't that inner circle usually tangent in only one point for the case of a shaft and the outer circumsribed on the outside profile and the other way round in the case of a hole? Those boundary circles have to be concentric so that would seem natural, which is not apparent from the picture shown.

[@Gdandtbasics]

For circularity, the tolerance zone circles are always concentric and can change in size, they are only required to be separated radially by the specified distance. Subsequently, Rule #1 will check the envelope of the feature to an envelope defined by the largest size for and external feature. And any 2-point measurement accross the diameter of the feature cant be smaller than the smallest size defined by the size limits for an external feature. This all means that the rule #1 will always at least control circularity to the amount of total size tolerance.

[@eartheartbaratheon791]

@@Gdandtbasics Thanks for the answer. I get what you're saying, I'm just pointing out that when you present a three-fold symmetrical feature like at 5:00 you're suggesting (involountarily) that both circles are tangent at 3 points with the profile, which is basically never the case I think. That's all.

[@amolpshende]

Can you show how adding circularity refinement will affect the available tolerance zone?

[@Gdandtbasics]

Using circularity as a refinement to something like the position of a bore would only refine the form of that cylinder. The circularity tolerance zone would still be to concentric circles at radially distanced apart by the tolerance value of the circularity callout these two circles are NOT located in relation to anything else, and no datums will be involved. Keep in mind that if you are using it as a refinement, it must be more restrictive that the form already controlled by Rule #1.