I think I figured it out. I did some testing offline creating circles with different diameters, constructing a cylinder and dimensioning cylindricity to see how the diameters of different sizes affect it.
No. The diameter can be larger or smaller than it's supposed to be and it will fail it's size specification but, so long as the difference between the largest and smallest
Wait, so a cylinder diameter that is larger than the diametric tolerance will also be out of tolerance for cylindricity? I'm sorry I don't understand
No. What I meant was, under ASME, if no cylindricity tolerance is shown, then the size tolerance also controls the form and the maximum permissible form error cannot exceed the total size tolerance. For example, if your size tolerance was ±0.1, then the total allowable form deviation would be 0.2 - when the smallest measured diameter was exactly at the lower limit and the largest measured size was exactly at the upper limit.
Designers are allowed to further refine things by adding a cylindricity tolerance if required, but that cylindricity tolerance must be smaller than the total tolerance already specified for size. Using the same example as above, they could add a cylindricity tolerance that is less than 0.2 to control the form more tightly.
Cylindricity is simply the allowable range between the maximum and minimum size measurements. Those actual sizes can be oversize or undersize and the cylindricity could still pass, so long as the range between max and min did not exceed the cylindricity tolerance.
