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Circular runout

Circular runout

(OP)
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?


RE: Circular runout

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.

RE: Circular runout

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

RE: Circular runout

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

RE: Circular runout

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

RE: Circular runout

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?

RE: Circular runout

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

RE: Circular runout

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? ........


RE: Circular runout

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

RE: Circular runout

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

RE: Circular runout

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.

RE: Circular runout

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.

RE: Circular runout

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

RE: Circular runout

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).

RE: Circular runout

Quote (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.

pmarc,
Here you are

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

RE: Circular runout

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

RE: Circular runout

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

RE: Circular runout

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........


RE: Circular runout

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

RE: Circular runout

mkcski,
If on ISO drawing a feature of size does not have any form conrol applied (either directly through tolerance frames, or indirectly - for example by invoking a standard with general geometrical tolerances), then the form of that feature of size is not controlled at all. Is this what you were asking for?

RE: Circular runout

Quote (ASME Y14.5-2009 para. 1.3.31)

derived median line: an imperfect (abstract) line formed by the center points of all cross sections of the feature. These cross sections are normal (perpendicular) to the axis of the unrelated actual mating envelope.

How is the center point of a cross section determined?

pylfrm

RE: Circular runout

"To derive the median line, one must (at least in theory) take and "infinite" number of cross-sections, find the centers of each of those cross sections, and connect the centers together. The result would be an imperfect "spline" (like a noodle). So, you could have a part with large surface straightness and perfect DML straightness. Picture "barrel-shaped" pin. So, surface straightness controls DML straightness, but DML straightness does not control surface straightness. As long as the out-of-straightness of the surface is symmetrical, the DML stays straight."

"DML straightness (done correctly) can be a time-consuming thing to measure, but can be done with a CMM. Often we will just "estimate" (and what measurement isn't just an estimate anyway) the DML straightness by measuring the minimum circumscribed cylinder diameter (can be done with a comparator or a CMM) and take the difference between that value and the local diameter measurements. Often, DML straightness is specified with an MMC modifier, so then it could simply be gaged (or checked with a dial indicator and some gage blocks."

---per Mark Foster on linkedin website



RE: Circular runout

And a question for pmarc,

Why D1, B2, I1 and G2 are not considered redundant (or in conflict / incompatible)?

Just me trying to understand.

RE: Circular runout

pylfrm:

Regarding finding the center point:

Y14.5 is a product definition standard and consequently does not define manufacturing or inspection methods. Given too that there is no discussion about how to determine the center at each cross section, I could go in several directions to find the center points and "connect the dots". I could suggest: 1) the axis of the smallest circumscribed circle; 2) a complicated surface analysis to "remove" form error (like for Concentricity), 3) a best material condition FIM using a dial indicator and a select number of opposing locations, 4) best-fit circle using CMM algorithms ....take your pick.

Certified Sr. GD&T Professional

RE: Circular runout

Determination of the center should be covered in Y14.5.1

RE: Circular runout

Quote (pylfrm)

How is the center point of a cross section determined?

This is a good question. And I wouldn't agree with mkcski here. Although it is true that Y14.5 is a product definition standard, certain things should/must be defined in it. If there is a definition - Derived Median Line in this case - that says that certain center points must be found in order to determine/find the actual DML, the definition should clearly specify (either directly or indirectly by giving a reference to another document) how to establish the center points. This is not what is currently happening in Y14.5-2009. What is the reason that the committee was able to give clear definition of, for example, Feature Axis (which is of course extremely useful in determining actual position or orientation errors), but was not able to offer a hint on how to find the center points constituting the DML? This I would really like to know.

The interesting thing is that in Y14.5M-1994 the definition of the DML had a statement: "The cross section center points are determined as per ANSI B89.3.1". This is the standard for Measurement Out-of-Roundness amd in that document four different methods of establishing the center point have been defined, as given in para. 2.8:

2.8 Centers for Out-of-Roundness Measurement
The centers of the measured polar profile which may be used to determine the out-of-roundness value when specified are those related to one of the following alternative methods of out-of-roundness assessment:

2.8.1 Minimum Radial Separation (MRS). Tis center is that for which the radial difference between two concentric circles which just contain the measured polar profile is a minimum1.

2.8.2 Least Squares Center (LSQ). This center is that of a circle from which the sum of the squares of the radial ordinates of the measured polar profile has a minimum value.

2.8.3 Maximum Inscribed Circle (MIC). This center is that of a largest circle that can be inscribed within the measured polar profile2.

2.8.4 Minimum Circumscribed Circle (MCC). This center is that of the smallest circle which will just contain the measured profile3.

1This is also known as the center for minimum Total Indicator Reading (TIR). The British Standards Institution publication 3730:1964 refers to it as Minimum Zone Center (MZC).

2This is also known as the plug gage center and is generally used for internal diameters.

3This is also known as the ring gage center and is generally used for external diameters.


I am not sure why exacly pylfrm asked the question about the center points, but with all of what I just said, I don't think that different methods of establishing the center points (potentially leading to different actual DMLs) could change anything in the answer to greenimi's question.


Quote (greenimi)

And a question for pmarc,

Why D1, B2, I1 and G2 are not considered redundant (or in conflict / incompatible)?

Why are you only asking me? If I am seeing correctly, mkcski gave you exactly the same answer. wink

But seriously, the reason these four cases are ok is because it is possible, although quite unlikely to happen, to have a cylinder produced with maximum allowable DML straightness error, say .010, that will also give the actual circular/total runout reading of .010. This can happen when the axis of the Unrelated Actual Mating Envelope (UAME) of such cylinder is perfectly coaxial with the datum axis (the cross-sectional form of the cylinder would also have to satisfy certain requirements).

RE: Circular runout

Apparently B89.3.1 has it's own set of FCF modifiers. I haven't got a copy, but Jim Meadows mentions it in his book:

https://books.google.com/books?id=Ms7lVOepeNsC&...

Measurement of Geometric Tolerances in Manufacturing By James D. Meadows

ISBN-13: 9780824701635
ISBN-10: 0824701631
Publisher: CRC Press
Publish Date: June 1998
Page Count: 455

RE: Circular runout

(OP)
Pmarc,
Quick follow-up:

You said (and please correct me if I am wrong):
The circular runout is controlling Derived Median Line if the circular runout tolerance is smaller than cylinder size tolerance. Correct?

If the circular runout tolerance is NOT smaller (and is bigger) that cylinder size tolerance than consequently is NOT controlling the DML. The quick question is: then what is controlling the DML is this later case.
Probably, you will say…sic…the DML callout. Right? If not, please correct me…. I can stand corrected….

So, the DML can be any amount? (any functional amount to be more precise)?

In this case (when a DML is specified) the surface form is left uncontrolled? I would say no. Since rule#1 is no longer applicable, then the circular runout will control the form surface and even if circular runout is bigger than the size tolerance is still controlling the DML. (regardless of the cylinder tolerance size or the circular runout tolerance)

I know……………. , it does not make any sense my explanation.

RE: Circular runout

You see pmarc….. I am not the only one who is addressing the questions only to you.

And I know why……….. and you know why too…

Because your knowledge, experience and ability to explain in the layman terms / too all level of education. I developed such of level of trust in your opinion that is like “if pmarc said so, that must be true”. No more questions or doubt.

RE: Circular runout

gabimot,
Just to make sure that we are on the same page, I indeed said that: "The circular runout is controlling Derived Median Line if the circular runout tolerance is smaller than cylinder size tolerance", but this was the answer given for a scenario assuming that no direct DML straightness callout was shown on the drawing.

If, however, the DLM straightness callout is directly specified in addition to the circular runout tolerance, then that statement is no longer always true. As long as the DML straightness tolerance value is smaller than the circular runout tolerance value, the circular runout callout will not be able to directly limit the straightness error of the DML - see greeinimi's examples B2, C2, D2, E2.

So if you are asking what controls the DML if the circular runout tolerance is bigger than the size tolerance AND no DML straightness callout has been explicitly specified, my answer is - it is the size tolerance (assuming Rule #1 is in charge).


greenimi,
I can only say thank you once again.

RE: Circular runout

To all who engaged:

I really appreciate this in-depth discussion into this little used DML concept. I have a much better appreciation of the this "gray" area.

I totally agree with greenimi in his kudos to pmarc. Pmarc is the "man". If this "group" ever gets together for a meeting (not sure if this allowed), we need to give him some sort of SPECIAL recognition for sharing his wealth of information in such a concise and clear manner

Certified Sr. GD&T Professional

RE: Circular runout

Quote (pmarc)

I am not sure why exacly pylfrm asked the question about the center points, but with all of what I just said, I don't think that different methods of establishing the center points (potentially leading to different actual DMLs) could change anything in the answer to greenimi's question.
I asked to point out a shortcoming of the standard, to hopefully gain some insight (thanks for the ANSI B89.3.1 reference), and because I came up with a different answer for some of greenimi's scenarios. If the DML is determined using minimum circumscribed circles, then I think it is possible to meet a size tolerance (with envelope requirement) of 0.005 and a total runout tolerance of 0.005, but have straightness error of greater than 0.009. This requires non-circular cross sections.

pylfrm

RE: Circular runout

Quote (pylfrm)

... and because I came up with a different answer for some of greenimi's scenarios. If the DML is determined using minimum circumscribed circles, then I think it is possible to meet a size tolerance (with envelope requirement) of 0.005 and a total runout tolerance of 0.005, but have straightness error of greater than 0.009. This requires non-circular cross sections.

I am afraid I don't understand something from the above:

1. Why did you say "(with envelope requirement)"? In greenimi's scenarios there is no envelope requirement as far as I see - it has been overriidden by the DML straightness callout.

2. Even if we assume for a moment that the envelope requirement is in charge (we would then also have to assume that there is no explicit DML straightness callout applied on a drawing), could you describe in more details how in your opinion it is possible to have straightness error greater than total size tolerance, and how it is possible to have straightness error greater than total runout tolerance?

RE: Circular runout

pmarc,

To clarify slightly, I am interpreting "DML Redundant" to mean that the straightness tolerance c is greater than the maximum straightness error possible in the absence of the tolerance. I am assuming the envelope principle applies to the size tolerance if the straightness tolerance is removed.

I probably should have said "(with or without envelope requirement)".


For more details on the statement in my previous post, see attached image. Due to software limitations, dimensions are in units 1000 times smaller than greenimi's, and circles look rather polygonal.

The cross section (shaded in dark blue) is bounded by two arcs. The first is the size tolerance envelope boundary, has diameter 100.000, and is centered on the datum axis. The second is the minimum circumscribed circle of the cross section, has diameter 99.544, and is centered 4.772 away from the datum axis. Imagine every cross section of the feature is this shape, but the direction of decenter of the second arc varies through 180 degrees or more over the length of the feature.

I believe this feature meets a size tolerance of 5.000 and a total runout tolerance of 5.000, but has DML straightness of diameter 9.544.

pylfrm

RE: Circular runout

pylfrm,

Thank you for clarification.

Unless I am missing something in your explanation and the picture, I would disagree that the feature shown (with the cross-sectional decenter varying along the axis in a way you described) has actual DML straightness error of dia. 9.544.

In my opinion the DML straightness error is 0. It is simply because in each cross-section the center point that contributes to the overall shape of the DML should be derived from the center of the minimum circumscribed circle (which is always of diameter 100.000, and not 99.544) that does not change its location between the cross-sections.

One way, as far as I imagine, you could get the DML straightness error of 9.544 for this particular geometry would be if you started offsetting cross-sections relative to each other, so that, for example, the center point of the cross-section at one end of the feature would be offset from the center point of the cross-section at the other end by 9.544. But then this geometry would not be able to meet the total runout tolerance of 5.000.

RE: Circular runout

pmarc,

Why do you say the minimum circumscribed circle is of diameter 100.000? Which portion of the cross section do you believe would fall outside the circle of diameter 99.544?

pylfrm

RE: Circular runout

pylfrm,

I stand corrected. I had to sketch your example in my CAD software to see that you are right. The minimum circumscribed cylinder diameter is indeed 99.544, and the DML can behave exactly in the way you described it. Thank you for showing this - really an eye-opener to me.

RE: Circular runout

pmarc,

Glad to hear.

The main thing I take away from this, and other similar discussions on this forum, is that there is often not much value in trying to interpret the control provided by one type of tolerance in terms of another. Things quickly become more trouble than they're worth.

pylfrm

RE: Circular runout

That is true, but still these are good theoretical exercises. They definitely help to keep a sharp mind and sometimes (like in this case) expose to totally new aspects of the problem.

RE: Circular runout

pmarc and pylfrm,

So, how the new revelation will affect the outcome of the thread, or the answers to the chart I have posted?
Pylfrm said somewhere :".......and because I came up with a different answer for some of greenimi's scenarios"


I have to admit I do not understand
"The cross section (shaded in dark blue) is bounded by two arcs. The first is the size tolerance envelope boundary, has diameter 100.000, and is centered on the datum axis. The second is the minimum circumscribed circle of the cross section, has diameter 99.544, and is centered 4.772 away from the datum axis. Imagine every cross section of the feature is this shape, but the direction of decenter of the second arc varies through 180 degrees or more over the length of the feature.

I believe this feature meets a size tolerance of 5.000 and a total runout tolerance of 5.000, but has DML straightness of diameter 9.544"


Yes, you can explain it to me, but you cannot understand it for me......so I am still working on itbanghead

RE: Circular runout

greenimi,
I will leave pylfrm the explanation - after all, he holds rights to this revelation winky smile

And yes, it will change answer to your question. In fact, I think it will change answer to initial gabimot's questions too.

When it comes to your scenarios, looks like the only redundant cases are: A1, B1, F1 and G1.

As shown and explained by pylfrm, the actual DML straightness error can be almost twice as big as actual total (and circular) runout error, but no more. In A1 & F1 it is c=.011 vs. b=005, and in B1 & G1 it is c=.010 vs. b=.005.

pylfrm,
Feel free to correct me.

RE: Circular runout

Quote (pylfrm)

The main thing I take away from this, and other similar discussions on this forum, is that there is often not much value in trying to interpret the control provided by one type of tolerance in terms of another. Things quickly become more trouble than they're worth.

Quote (pmarc)

That is true, but still these are good theoretical exercises. They definitely help to keep a sharp mind and sometimes (like in this case) expose to totally new aspects of the problem.

Like someone said here on the forum: makes a good mental exercise which prevents Alzheimer…allegedly.

I am waiting for pylfrm for his explanation..... how did he get that..............

RE: Circular runout

pamrc:

Quote (pmarc)

I stand corrected. I had to sketch your example in my CAD software to see that you are right. The minimum circumscribed cylinder diameter is indeed 99.544, and the DML can behave exactly in the way you described it. Thank you for showing this - really an eye-opener to me.

I have been following this thread. The word discussions alone are a little hard for me to visualize and the related attachments add much to my understanding. You mentioned in the above quote you did some CAD work to convince yourself of pylfrm's analysis. I do not have CAD available. Could you please attach the CAD drawing in JPG format so I can follow your understanding?

Certified Sr. GD&T Professional

RE: Circular runout

greenimi,

Before I attempt to give answers for the scenarios in your chart, could you please clarify what "DML redundant" means to you? I posted the interpretation I was using earlier, but it appears pmarc is using a different one which does not involve the envelope requirement.

As for further explanation, I'm not sure where more detail is desired. If anyone has a specific question, ask away.

The constraint solver in SolveSpace, which is free software, was used to calculate the numbers and create the image I posted.

pylfrm

RE: Circular runout

pylfrm,

Consider a two steps cylinder--as shown in my attachment from a couple of days ago.
The "big" OD is dimensioned with a feature of size requirement and the size is within .010 (for example), then has a circular runout within .005 (for example again) relative to the small OD (datum feature).
Now, the designer want to add a derived median line, let's say .010 (consider there is a functional reason for that.... do not ask why)

The question is: is the DML (derived medial line) callout even necessary or the combination of the size+ circular runout will cover / will ensure that the DML is smaller than .010?

Does my explanation holds any water? If not, please let me know... bigsmile

Thank you again for being patient and explain to us what you've found.......

RE: Circular runout

greenimi,

I agree with pmarc that the DML straightness tolerance is redundant in cases A1, B1, F1, and G1. Your latest question is case B1, so this should answer that. I also agree that the DML straightness tolerance is not redundant in cases C1, D1, E1, H1, I1, J1, C2, D2, E2, H2, I2, and J2.

Your intended meaning of "DML redundant" becomes important for cases A2, B2, F2, and G2:

If the straightness tolerance is not applied and the envelope requirement is in effect, then I think the maximum DML straightness error will be slightly less than 2*min(a,b).

If the straightness tolerance is not applied and the envelope requirement is not in effect, then I think the maximum DML straightness error will be slightly less than b+min(a,b).

Note that I have not thoroughly confirmed these last two statements.

pylfrm

RE: Circular runout

greenimi, mkcski,
Have you been able to visualize what we have been talking about?

mkcski,
I wish I could post a sketch of what I did in my CAD software, but that is unfortunately impossible. The reason is that by "my CAD software" I meant the software I use at work. Due to security reasons I am not allowed to publish anything I create there in the internet. But you should definitely try the link to the SolveSpace solver that pylfrm offered. This thing is for free, does not require installation, and although quite crude (comparing to more advanced CAD systems), it allows to simulate/see things that have been discussed here.

pylfrm,
About your last two statements... for greenimi's scenarios, why are you considering situations in which the DML straightness tolerance is not applied? If I understand the question correctly, he is not asking what happens if the DML straightness is or is not applied. He wants to know at which point exactly applying the DML straightness does not make sense any more.

RE: Circular runout

pmarc,

Quote (greenimi)

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

To determine whether a tolerance is redundant, one needs to know what will happen if it is not applied.

pylfrm

RE: Circular runout

pylfrm,

More important, one needs to know what will happen when the acceptable variant parts are installed. It seems unlikely that the combinations mentioned would be used in the way they have been examined.

Without seeing an application and surrounding analyses it's sort of odd to consider something like this. So far there's no reason to apply any tolerance type, much less values.

RE: Circular runout


Pylfrm and 3DDave,

This is a theoretical exercise .... Lets say a test question, to evaluate the theoretical knowledge in different callouts. No practical application to be provided as I don't have a such in my mind.

RE: Circular runout

And by the way, pmarc got my question right.... Yes I would like to know that point..
"He wants to know at which point exactly applying the DML straightness does not make sense any more."

RE: Circular runout

pmarc:

Thanks for the tip on SolveSpace. I need to see our IT guy to see if I can install this on my PC.

Certified Sr. GD&T Professional

RE: Circular runout

Pylfrm,

Just to restate again:
....... at which point exactly applying the DML straightness does not make sense any more?

Could you, please, explain in the layman therms "your discovery" / little known revelation?


Thank you again for your help and patience.


RE: Circular runout

I guess this is an excellent question for the certification exam (2009, as that’s the one using the “I” symbol). My opinion.

I am not sure about the “correct” answer: If I have to answer, I would say that the worst surface straightness is limited by the total runout (of course for the total runout case).

However, for the circular runout case, gets more complicated.

Could be the size tolerance combined with the circular runout tolerance? (.010+.005) or
half size circular runout + size tolerance (.0025+.010)
or even double the circular runout tolerance (2x 0.005)

Anyone can help? Any GD&T experts could chime in, please?

Interesting question anyway……….

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