Concentricity ASME

[[To...]]

Any thoughts on how to get Calypso to measure concentricity per ASME Y14.5? As I understand the standard, it is looking for all of the median points of diametrically-opposed elements of the feature. Or, can I just get away with using Calypso as is?

[[Jo...]]

I know I don't have an answer for you but based on your other post about a questionable datum reference frame, I'll comment. Whenever I see a concentricity callout on a drawing, I pretty much assume it has been misapplied unless I can see where position would not work. That has actually never happened in my entire 30 year career. I know another member of the Y14.5 committee whose career was 45 years and he had never seen it properly applied. This is one reason that neither concentricity, nor symmetry will be in the next version of the standard. They are essentially useless. Concentricity had two redeeming qualities that have now been negated by modern technology and also by a new symbol. Symmetry had no redeeming qualities.

If you have the luxury of contacting the customer and asking about this, you should. It's likely that position is really what they are after.

[[Cl...]]

Doesn't the standard also recommend to use position, or profile before specifying concentricity?

[[Ma...]]

I generally switch it to position. Same formula but now I can give the X, Y, or Z deviations (Additional Position Result).

I change the title to read Concentricity because I know they are just scanning for green or red on the printout and when they see concentricity in the name they rarely question it.

I don't think any CMM software checks concentricity correctly per the spec. You could take equidistant points along the diameter by using a formula with loop and ask for the median points and recall these points into a circle. This circle would then need to be smaller than your concentricity callout but you still have the issue of reporting its location to its theoretical nominal position. Using Positional tolerance is just easier and gets the job done.

Mark

[[Me...]]

I tend to agree with both John and Clarke. Since I first sat down at a CMM in 1990 I have seen 'some' concentricity callouts on drawings. I can't think of an instance where it seemed to be applied correctly. It 'appeared' they were looking for TP. I'm older now and about to retire and feel like I can give my two cents worth without too much opposing flack! The term 'concentricity' is an old term and has been used for years, well before GD&T existed. I want to put part of the blame on the GD&T committee for adopting that same 'old' term in which to express different results. In other words, the 'old' version of 'concentricity' usually meant 'same centers'. Most of us would call that true position. There may be valid reasons to apply GD&T concentricity, but I feel they should have named it something else. I've seen examples of Calypso results for concentricity and true position, of the same features and they display the same results. I won't say Calypso is wrong, but 'suspiciously' questionable. I've always considered concentricity applicable to 'high speed rotating' parts, like maybe an electric motor shaft or a cam shaft. So even though I don't like stepping out on that limb of not measuring/reporting exactly what the print calls for (I am not allowed to contact the customer and clear it up as should be done), there are times that I've used true position for a GD&T concentricity callout (sounds like a confession, doesn't it!?). But when you have a 'U' shaped part that bolts down on the bottom of the 'U' and holes in opposing sides in line with each other called out with concentricity, I have to shake my head. We've all 'been there, done that' and you do the best you can do regardless of someone's misinterpretation of how it probably should have been labeled. Over the years I kept thinking that it would get better. Well, it hasn't yet! So I will leave the battle for the next generation (including y'all) to try to change the mindset of those who create the drawings and blueprints in which we report results. Good luck to all.
I am now stepping off my soapbox and yield the floor...
🙂

[[Ch...]]

The great Ryan Stauffer created a macro that would calculate true ASME concentricty. I have it saved on here somewhere but currently can't find it(shows you how much I use it). Also, I have attached a lunch-learn about concentricity that gives a good explanation of concentricity across a distance too.

Profile_Concentricity_CALYPSO.pdf

[[To...]]

I'm on board with everyone's comments. Historically, I have always believed the use of concentricity was determined for rotating parts and position was for static parts, even though the results were the same.

We're currently courting a potential new Zeiss customer. I just noticed they're a vendor for a large aerospace company. So, even though I can refer to the "use position" quote in ASME, we may have to meet yet another interpretation by the aerospace company. I'm just looking to be prepared for the discussion if it comes up.

The late Don Day of Tec-Ease famously quoted "When in doubt, use run-out".... which was from one of his videos discussing concentricity vs run-out.

[[Cl...]]

Evaluated as concentricity, position, profile, radial runout.

[[Ri...]]

I know Umess was incorrect for concentricity. It delivered the same answer as position. It was the same with early versions of Calypso that I tested. The testing I've done with my offline station would indicate nothing has changed. That being said, I have a routine that satisfies ASME and doesn't increase runtime overmuch.

[[An...]]

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[[Br...]]

I believe this is the macro that Chad is talking about. I've honestly never used it though so good luck and let me know how it works if you use it.

realconc.zip

[[Pe...]]

Y14.5-2009 defines concentricity as "that condition where the median points of all diametrically opposed elements of a surface of revolution... are congruent with a datum axis...".

What is a "diametrically opposed element"?

[[Cl...]]

[[An...]]

_

[[Cl...]]

Downloaded 8 times, what the heck happened?

Jesus Christ what?

[[Pe...]]

If a feature isn't truly round, as no real feature is, what is the process to decide that two points are, or are not, diametrically opposed?

[[Pe...]]

Jesus Christ probably had a rigorous definition for a diametrically opposed element of a surface of revolution, but his Apostles didn't record it so we have to work it out here on the internet.

[[Jo...]]

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You can touch off any point on a diameter, then touch off another point that is 180 degrees away and along a vector that passes through the datum axis. That will be diametrically opposed. It doesn't matter if the part is perfectly round or not.

[[Pe...]]

Thanks, John. So then would it be correct to say that, within a planar cross section, two points are diametrically opposed if a line drawn between them intersects the datum axis?

My questions center around whether a "diameter" drawn between the two points should pass through the datum center or the local feature center.

[[Jo...]]

Yes. Technically it should be the centers of all diametrically opposed elements in the cross section. This is not practical so we just do what we can. To your point though, if we took 10 readings on a single cross section, the points would likely make a circle, albeit a very small one. All those points have to be within whatever the diameter of the tolerance zone is.

Oh, and the vector has to pass through the datum axis so the derived point won't likely be on the datum axis.

[[Pe...]]

It's only one example - one shape with one offset from the datum center - but I'd be curious to see how Andreas' pentalobe example comes out with the points diametrically opposite with respect to the datum instead of the local center.

Something like this(?):