Parallelism between coaxial cylinders? 1

[rkrz]

Please see the image attached. This would be a cross section of the cylindrical part.

I am trying to figure out the best way define the 'parallelism' between 3 diameters of a part, more specifically defining the tilt of the middle diameter to datums A-B. The initial thought was to use a total runout with tight tolerance, however, due to the many factors that influence this, I don't think it is ideal. Would it be acceptable to define that diameter with a parallelism to A-B? Or maybe a cylindricity paired with a more open runout tolerance? Please let me know. Thanks.

https://files.engineering.com/getfi...4cc4-41ba-a578-4fc0e9e73619&file=example1.PNG

 

[Belanger]

The options you propose all sound valid, but they will have significant differences. That's because parallelism is merely an orientation control; it doesn't control form (roundness/circularity/cylindricity). If you go with cylindricity, that's merely a form control (doesn't control parallelism since it never references a datum). If you go with a runout tolerance, you'll get more bang for your buck... it controls location, form, and orientation. But it might be overkill to muscle all three of those ideas into a single tolerance.

So it depends on the quality (or qualities) you think need to be controlled: form, orientation, location, size, or a combo of some of those.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[Eric Gushiken]

I think your plan of using total runout to control it in reference to A-B sounds good but B may also need to be controlled in relation to A.