Circular runout 2

[gabimo]

Is circular runout controlling:
1.) Straightness of the cylinder surface?
2.) What about Derived Median Line (DML)?

Same questions for total runout:
Is total runout controlling:
3.) Straightness of the cylinder surface?
4.) What about Derived Median Line (DML)?

In other words, if a cylinder surface (surface feature A) has a circular or total runout shown (in relationship to a datum axis defined by other cylindrical surface, feature B) and a straightness callouts or a derived medial line callouts for the surface feature A are also shown, does the straightness or DML should be smaller than the circular/ total runout?

 

[pmarc]

1) No. Straightness of linear elements of cylinder surface is limited by size tolerance (through rule #1).
2) Yes, if circular runout tolerance is smaller than cylinder size tolerance.

3) Yes, if total runout tolerance is smaller that cylinder size tolerance.
4) Yes, if total runout tolerance is smaller that cylinder size tolerance.

 

[mkcski]

gabimot:

Let me add some overall definition to pmarc's specific answers. Runout is a composite control. For surfaces of revolution, it controls position (coaxiality) between the datum feature (axis) and the feature under control AND simultaneously controls the form of the features' surface. So the FIM reading is always a combination both errors - as nothing is perfectly formed or positioned. As pmarc said, when the Runout tolerance is smaller then the size tolerance the Runout reading limits the form to that value; however, because Runout is a composite control, if the position component of the FIM is equal to the Runout tolerance, the surface must be perfectly formed (circular for circular or cylindrical for total) to be acceptable. The converse is the same - if all form error the surface must be perfectly positioned.

When the Runout tolerance is greater than this size tolerance the form error is limited but Rule #1 and the remainder is all position. In these situation it can be a tough call to apply Runout or use Position and let the Rule #1 control form independently. The main determination should be weather function and fitup requirements are surface or axis control driven.

Runout can also be applied to surfaces 90-degrees (normal) to the datum axis. It is still a composite control, but instead of position, it controls orientation and form.

Certified Sr. GD&T Professional

 

[greenimi]

Well, No rule#1 applicable when DML used (question 2 and 4)

 

[mkcski]

greenimi:

I agree, but the questions #2 & #4 is do not apply to/with Runout. To my understanding DML is not associated with Runout as it is a surface control - not axis.

Certified Sr. GD&T Professional

 

[greenimi]

mkcski,
I agree, but the OP question was if the circular runout controls the DML?

So it is a yes or it is a no?

Or it is a conditional yes or a conditional no?

 

[mkcski]

greenimi

I was not interpreting the question that way. But now that you mention it....not conditional at all.... DML does not apply to Runout... it is surface analysis not axis.

Certified Sr. GD&T Professional

 

[greenimi]

I would say...no so fast:

Since you derive the median line from the surface, there is no way that the DML straightness could ever be greater than the surface straightness.
Now, the question for you: what is controlling the surface straightness? ........

 

[mkcski]

greenimi:

Who cares about DML with Runout - the two are in different worlds - surface vs axis. But let me consider your question and back to you this week.



Certified Sr. GD&T Professional

 

[greenimi]

I do care! I am trying to avoid, for example, a redundant callout!

 

[3DDave]

Every control has some side effect, but it isn't clear there are practical uses in determining just what those effects are, beyond making up test questions. It's not like QA/QC will ever add a side effect of a control to a report.

 

[pmarc]

greenimi,
Could you try to make up some scenarios? We could then try to find an answer whether the callouts shown are redundant or not.

 

[Belanger]

While pmarc's initial answer seems to be correct to me, I agree with mkcski that runout never directly controls an axis or DML, so it's strange to try to make a direct connection between the values.

With circular runout, each cross-section could have a very different size, but the center point of each cross-section will be somewhat accurate. The derived median line essentially connects all of these center points, so even circular runout can impact the DML, I suppose.

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

 

[pmarc]

J-P,
The way I understand OP's question is that she/he wants to figure out whether it makes sense to apply additional straightness callout (surface straightness or DML straightness) when a circular or total runout callout has been already applied to a cylindrical feature.

It is true that both types of runout do not directly control the DML, but, as you said, they may have impact on it, thus there may be cases where an explicit DML straightness callout is redundant when combined with a runout callout.

One example would be a combination of DML straightness of dia. 0.2 and total runout of 0.1. Since the actual DML straightness error can't be greater than 0.1 (otherwise considered feature will violate the total runout requirement), the explicit DML straightness FCF should not be there.

On the other hand, as weird as it may sound, I wouldn't see a problem with a combination of DML straightness of dia. 0.1 and total runout of 0.1 (let's not talk about functional reasons of using such combo, please).

 

[greenimi]

greenimi,
Could you try to make up some scenarios? We could then try to find an answer whether the callouts shown are redundant or not.

pmarc,
Here you are

Hope this helps somehow. Lets talk about these scenarios/ cases

 

[greenimi]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1489502229/tips/Circular_runout_pmarc_g375ge.pdf[/url]


Better quality....maybe

 

[pmarc]

greenimi,
In my opinion the DML straightness callout is redundant in A1, B1, C1, A2, F1, G1, H1, F2.

 

[mkcski]

greenimi:

I only deal with DML straightness at the theory/concept level and never in practice, so I might be missing some important factors. But let me offer my interpretation based on my current understanding.

1) The size has no impact on the DML evaluation as it is a axis vs surface control.

2) The DML straightness error is the radial off-datum-axis distance times 2 to obtain the DML diameter. This is measured at each cross section normal to the datum axis.

3) The worst case for the DML would be the greatest off-datum-axis distance. This would exist when .005 or .010 FIM for runout is all position error (no form error).

4) Because the DML is being reviewed concurrently with runout, the off-datum-axis DML distance (diameter) is effectively equal to position error.

5) Given the above, any DML value in the table over the .005 or .010 runout tolerance creates an incompatibility / conflict ( I prefer not to use the word "redundant" as it implies an equality).

Note: In the cases where the runout tolerance is greater than the size tolerance, the form error is limited to the .005 size tolerance and any runout above .005 size tolerance (.010 - .005 = .005) can only be position error. But because I am assuming all position error and no form error the full .010 is available to the DML error.

6) So my "conflicts" list is : A1, B1, C1, A2, F1, G1, H1, F2.




Certified Sr. GD&T Professional

 

[greenimi]

I agree, but the complicating thing is that when DML is used (redundant, in conflict or incompatible) rule#1 is gone, so I have to wrap my head around that fact as well.

How that fact (no longer rule#1 in place) has an effect for the form error of the part.....I have to switch my brain to ISO thinking--ISO with no E symbol ...........

I know for pmarc is much easier to do that (switch the thinking between the two systems), but for me is not so easy........

 

[mkcski]

geeenimi:

I have not investigated "I" "Independency" either. OK...form is independent of size but what limits form??? The Caution note in 2.7.3 tells the tale - nothing unless something is specified - not good practice. Since ISO is "I" by default, there must be an interpretation or controlled form. I have a few ISO standards. Maybe I will take a look.

pmarc:

Can ya help us out with ISO (default "I") and what controls form.

Certified Sr. GD&T Professional