Eccentricity of crown

[[Ow...]]

I would like some feedback on how you might report the eccentricity of the crowned face of this tappet part.
What characteristic would Calypso use?

[[To...]]

On first looks, it appears to be an axial run-out. ???

[[Mi...]]

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Agreed, more or less. It's not technically the same, since it says to locate it in a V-block rather than rotate around a datum, but axial runout is probably the closest you can get.

[[Ke...]]

I wish I had an easy answer.... but all I have on the subject is this
https://sciencing.com/how-to-calculate- ... 51764.html

We ended up settling for calculating the deviation from the center of a datum feature (cylinder), to the center of the measured feature (circle), without including form error.

[[Ow...]]

Axial run-out is what I envision the designer intending.
I suspected I might be going down a rabbit hole bringing it up here but, I wanted an idea of what I might be questioned on and knew I'd get that here.
Knowing the date the print was created and how they checked it, I don't imagine they even thought about the part ever being elliptical.
Thanks for your input.

[[Ke...]]

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I guess, anything is possible... but "eccentricity" would be a very odd term to use, for axial runout.
Using the most basic definition: "deviation of a curve or orbit from circularity" the most basic evaluation that I would emagine someone to intend would be Roundness (often called "out of round")

[[SH...]]

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Drawing without GDT is like food without salt. 🤣

[[Ow...]]

George Orwell actually wrote a book about the year the print was produced.
Up until this part, everything I'd dealt with concerning eccentricity involved cylinders.

[[Pe...]]

The bit about circles and conic sections is correct in a mathematical context but doesn't apply here. Eccentricity on mechanical drawings has to do with one round feature being off-center from another round feature. Eccentricity isn't defined anywhere in Y14.5, but it first shows up in the paragraph on concentricity in the 1982 standard and stays there until 2009. The usage implies something like coaxiality - features having a common center line (or deviation from it). In 2018 they dropped concentricity all together, but the word "eccentric" shows up in figures 12-2 and 12-4, and the meaning is similar. A quick online search for "eccentricity gd&t" suggests the same.
They're trying to control how much the spherical diameter of the crown can be off-center to the main OD of the tappet. The instructions in the note provide an indirect way for using bench tools to indicate the amount of off-centered-ness.
"THE CROWN MEASURED AT THE GAGE RADIUS" mean the height of the crown from the peak to the gage radius. If you zero out an indicator at the peak of the crown (LINE Y on the print), then offset the indicator straight down by .500, you should get an indicator reading between .0015-.0022 as you spin the part, watch the needle wag, and take the mean. They further refine this by requiring a total indicator movement of not more than .001. You could also achieve this on a visual comparator.
You might try using the tappet OD and the highest point of the crown to setup an alignment, then put a plane on the crown end with a circle scan exactly .500 out from the center of the tappet. All the points need to be between .0015-.0022 from the tip, and they all need to fit between two parallel planes .001 apart and square to the OD. Maybe some sort of profile for the first part, and perpendicularity or runout for the second?

[[Ow...]]

I wish they had a two-thumbs-up emoji on here.
Thanks for the very articulate reply Pete.