Concentricity vs. Runout - Page 2

1. Originally Posted by JNieman
If you only meant for the hexagon to illustrate how concentricity can be perfect while form is horrible (like it was /supposed/ to be a cylinder but you ended up with a hexagon for hypothetical reasons) then sure, you've got it spot on.
This is what I was going for. I was mainly expanding off Halco's comment earlier.

2. Hot Rolled
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Concentricity is an absolute term, runout is a relative term.

3. Plastic
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There are important differences between runout, total runout, and concentricity:

Concentricity is how well a shape is centered on a theoretical axis, regardless of roundness. So a hexagon can theoretically be perfectly concentric to a datum axis while having huge runout due to the fact that it isn't round.

This is technically incorrect. Concentric is a geometric term, not a machining term. "Cone Centric" means circles made by slicing a cone with planes perpendicular to a line running through the focus, thus making circles with the same focus, but differing diameters.

A hexagon cannot be a cone, only a six sided pyramid, so therefore cannot be concentric.

4. Plastic
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Originally Posted by genther
This is technically incorrect. Concentric is a geometric term, not a machining term. "Cone Centric" means circles made by slicing a cone with planes perpendicular to a line running through the focus, thus making circles with the same focus, but differing diameters.

A hexagon cannot be a cone, only a six sided pyramid, so therefore cannot be concentric.
How about I add the term coaxial. Isn't this the same thing as concentric?

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Originally Posted by genther
A hexagon cannot be a cone, only a six sided pyramid, so therefore cannot be concentric.
7.6.4 Concentricity
Concentricity is that condition where the median
points of all diametrically opposed elements of a
surface of revolution (or the median points of correspondingly
located elements of two or more radially
disposed features) are congruent with a datum axis (or
center point).
"Surface of Revolution" means you're technically correct. However, the hexagonal example given previously was a purely hypothetical deviation from a circular shape. It's just showing how a control on form and location can differ. Nominally it should've been circular. The hexagon was an exaggerated example of deviation-of-form.

Examples of other exaggerated form variations can be Figures 7-60 and 7-61 in the 2009 standard.