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MMC on Datums for Runout

MMC on Datums for Runout

(OP)
I am in need of a clarification to a runout callout.

Datum -A- is a flat index surface.  (The mating part threads up against this surface.)
Datum -B- is a stepped shoulder diameter slightly larger than the external thread major diameter.

I have a runout on a conical surface that is
|RO|.002|A|B|

What I'm wondering is if I can use MMC for Datum -B- in the runout feature.  By doing so, I can design my gage to only the max diameter of the shoulder (Datum -B- ) and not require a collet in order to find the diameter RFS.  My theory in doing so is that I end up with more of a functional gage because the mating part indexes against -A- anyway.  Tolerance stack-up between the shoulder diameter (-B- ) and the mating part may result in a loose fit, so only the pitch diameter of the threads actually contacts.  And thus, the runout of my assembly is really going to be based on the flatness of Datum -A- and the mating surface so gaging to something similar is a reasonable functional check.

--Scott
http://wertel.eng.pro

RE: MMC on Datums for Runout

Circular and total runout reference the datum diameter in RFS according to ASME Y14.5M-94. One cannot use MMC here.

Sorry but no attibute gauge here.

If the runout was converted to positional in a MMC mode, then one could reference the datum diameter in MMC and now it would conducive to an attribute gauge.

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

If you are trying to control the conical surface, then circular runout at RFS is in order. As Dave said, you can't do what you're trying to do with a runout specification. If you simply must use an MMC modifier on datum B then you should specify profile of a surface on the conical surface and then reference datums A and B.

I don't think position is the answer here but maybe it is. Can you shed some light on your thought process Dave?

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: MMC on Datums for Runout

(OP)
We have actually considered chaging it to a positional tolerance, because then it would control circularity as well as straightness.  (Don't read too much into those in terms of the definition of them via Y14.5, I can't think of another word that adequately describes the concept.)  But the problem with changing the tolerance at this point is that it is a completely different philosophy of inspection for these parts, and the change to the tolerance stack-up for assembly will also have to be ammended, flowing into all the tooling and gaging for those components as well.

Profile on a surface may work very well.  I'll have to ponder that a bit and consider how to inspect it.  We usually use CMM or Optical Comparitor for profile inspection.  Both of those aren't possible.  We need hard gaging.

Thanks for the clarification on the runout callout.  It is the same as I interpreted.  Just hoping I was wrong.

--Scott
http://wertel.eng.pro

RE: MMC on Datums for Runout

Powerhound:

I am rethinking my suggestion to go to a positional tolerance.

In a conical situation, we have a height dimension to consider and this is never a factor in a cylindrical pin or hole. If the cone was in relatively true position but the height was too high, possibly the checking fixture would not descend all the way down. It may appear that the cone is out of position and, possibly, it may not be the case.

Positional is not a good replacement here. Unfortunately, I would stick with circular runout and then measure.

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

Use profile of a surface where the limits are the equivalent inner boundary and outer boundary from your original combination of size & runout.  Inspection is done exactly the same as if it was a runout control, but now you zero your indicator at the basic radius, and watch that your indictor doesn't exceed +/- half of the profile tolerance.  One setup and you're done for size, position and runout ... not bad, eh?

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

(OP)
That is fantastic.  You deserve a start for that.  Now if only management realized how much money you just saved them!

--Scott
http://wertel.eng.pro

RE: MMC on Datums for Runout

Jim,

I'm confused.  The considered feature is conical, not cylindrical - did you not notice that?

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: MMC on Datums for Runout

Tks Evan, I had missed it.  It's essentially the same answer though. The only geometric control that locates a surface is profile of a surface.  By establishing the datum axis and rotating the workpiece about the datum axis, you still have an absolute location where any point on the surface is supposed to be, and a tolerance zone normal to the conical surface in which the surface must be.  Vision-type systems are great for verifying cones.

While it is legal to use +/- tols to size a cone, I'd like to see how anyone measures accurately at opposing points.  Without referencing the datum, there is no way to ensure that the opposed points are directly opposed (i.e. a circular cross section instead of an elliptical one).  Again, a surface profile provides the size & runout controls in one setup.  You zero the indicator (offset from the datum axis at the basic radius at one end) and now instead of moving the indicator longitudinaly along the axis, you move the indicator longitudinaly at half the basic included angle of the cone.

It's been a rainy, chilly day here, so I decided to make some pretty graphics too.  Note: Marvin is from SolidWorks 3DContentCentral.
http://www.profileservices.ca/files/tidbits/thd1103_239358_1.pdf
http://www.profileservices.ca/files/tidbits/thd1103_239358_2.pdf
http://www.profileservices.ca/files/tidbits/thd1103_239358_3.pdf

In these graphics, Marvin will move the indicator normal to the basic (nominal) surface, as represented by the blue arrow.  The hazy brown cone represents the nominal (basic) geometry, and the green workpiece surface is the actual workpiece.

Please, no comments on Marvin's poor inspection methodologies ... he's new at it.

 

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

Jim,

Are these graphics intended to relate to the Original Post By Swertel?

If they are I cannot quite make the association.  It would seem that the conical surface should be positioned vertically and rotated about the base rather than the axis.
It is not readilly apparent as to what is the primary and secondary datum feature in the setup.  Could it be somehow clarified?

RE: MMC on Datums for Runout

Jim:

I would just love to watch someone try profile of a surface on a cone using a circular runout setup. The cone must be shown in basic dimensions along with either the angle or the taper end. Where would one place the indicator initially? How would one sweep the surface on a basic angle?

Circular runout is still best in the situation described.

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

Ringster,

You're right, Marvin's setup deviates from what was described in the original post.  The part appears to be chucked at both ends, but should be oriented to one end face first and then centered using one chuck.  I don't think it needs to be positioned vertically though, are you thinking that the part might sag due to gravity and affect the reading?  This shouldn't be a big issue on Mars.

It also appears that Marvin isn't holding the indicator perfectly normal to the surface and will get some cosine error.  In fact, in the first diagram it's apparent that the stylus isn't even touching the part at all!  And what's with the second indicator?  Is he going to be inspecting concentricity next?  Also notice that both indicators show exactly the same reading.  An odd coincidence.

The whole thing is fishy if you ask me.  It almost seems made up.

p.s. I'd like to hear Marvin say "Oh goody. My Mitutoyo Q-36 high-resolution dial indicator"
 

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: MMC on Datums for Runout

Evan:

You are correct about Marvins measuring method. I do like Jim's animated drawing although it isn't really correct.

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

No, the graphic doesn't reflect the datum scenario given in the OP.  The larger issue, I thought, was the question of using profile to control a cone.  As I have some existing models that I use for training & documentation, I decided to use them to illustrate how to verify a conical surface spec'd with a profile control.

The drawing would, indeed, show basic dimensions for the end diameters, the length (unless a FOS, in which case +/- tol could be used), and the included angle.

Verification methodology depends on what you have at hand.
1) runout stand inclined at half the basic included angle by using a sine bar or angle plate; this puts the basic profile to the horizontal (or vertical), and the indicator can then run in a straight line wrt the surface plate.

2) runout stand as shown in graphic, and indicator on an inclined guide rail (picture two vertical stand posts, and two cross rails which remain parallel to each other while skewed to the vertical posts; I haven't seen this one in use, but I have seen the setup).  I have also seen a single cross-rail, but don't like it as the indicator can pivot about the cross rail axis, thereby losing its angularity relationship wrt the basic profile geometry.

3) manual optical comparator, with the datum axis aligned horizontally or vertically; you offset the object from the center by the basic radial distance at either end, rotate the crosshairs & grid on the screen to the basic angle, then you can travers +X/-X or +Y/-Y until you get the limit of the surface at that section, or you can use an overlay with the nominal, min & max boundaries and see if the conical surface violates that boundary as you rotate it about the axis

4) an automated profile vision system rotates the workpiece about its datum axis at high rpm, and a light curtain & camera traverse longitudinally along the axis to establish the surface which is then compared electronically to the CAD geometries directly or to a manually entered basic geometry and offset boundaries.

Options #1 & 2 use basic inspection apparatus that should be available in pretty much any shop.  This reinforces how easy it can be to verify a surface profile with basic equipment.
Option #3 requires an optical comparator, but that's pretty common in most shops that I've seen.  Again, no real challenge with this methodology.
Option #4 requires a comparatively inexpensive piece of equipment which, in a production environment, saves far more on labor costs than its purchase price.
A CMM in scan or point mode can be substituted for an indicator if preferred.

Conical tapers are the bread & butter of the tooling and molding industries.  These and other methods are used every day for conical tapers.
As for profile of a surface vs size & circular R/O;
- Profile checks size, form, orientation & location in one setup and inspection process
- size is to be checked by Taylor's Principle (Full form at MMC, 2 pt check at LMC)
  - how do you know you got the actual circular cross-section rather than a skewed cross section?
  - how will you check form at each point?
- circular runout is a check at each cross-section perpendicular to the datum axis
  - what happens between these sections?  waviness along the length of the part (as my modeled workpiece) will not be detected by circular runout
- what if you want a large size tolerance, but need good form along the length of the workpiece?  Size & Circular Runout can't do this; you'd have to add a straightness control also, but that would only control single longitudinal elements, not the net effect.  Would you then add a circularity control as well?  Of course not because Form controls are nasty to verify.  The alternative is a composite surface profile, and the inspection apparatus would typically be a runout setup.


Now, Marvin is a difficult creature to work with, and he's still tentative about his job, so he's just moving into position.  As in reality, there will always be a bit of a cosine error as he can never truly get the deflection probe to a perfectly normal orientation to the basic surface.  

Marvin's second indicator is part of his Q2009 Inspection Modulator Probe, complete with aiming reticle & hair-trigger download of digital data.  Marvin would not, however, ever use his capabilities for the evil task of verifying concentricity.  ;~}

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

(OP)
Nobody likes to verify concentricity.  I don't even think Duck Dodgers could pull off the task; or his Eager Young Space Cadet.

I'm actually home with a sick child today.  I'll see when I get into the office tomorrow if I can dumb-down my original print to something non-proprietary and share a pdf of it.

--Scott
http://wertel.eng.pro

RE: MMC on Datums for Runout

For Duck Dodgers, just pronouncing the word "concentricity" would be enough of a challenge.

Evan better, imagine Elmer Fudd talking about the three different orientation tolerances.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: MMC on Datums for Runout

Jim:

I reviewed your methods and found each one, if they can be performed, much more difficult than circular runout.

1  Usually a divider head or chuck is horizontally mounted on a table and placing a sine plate (bar) under it is not possible. Maybe if one had a small portable chuck, but I have not seen one in my experience.

2  Using an inclined rail is possible if one used a metal lathe but they are not used as measuring instruments. If they were, each would have to be calibrated using the 10% tolerance rule.

3  This is possible but we are only measuring down the incline or taper rather than around the circumference. Should one rotate the part and perform this again? This could be really messy.

One could use a computer controlled CMM  and that is probably the way I would suggest if a profile of a tolerance is really required but is it. The questioner here wanted to use an attribute gauge rather than confirm the feature with a circular runout.

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

Dave, in each of those cases you'd be doing essentially the same as a circular runout, except that you are also verifying the size at the same time.

Your perspective seems fixed on large automotive parts.  Small & moderate-sized parts are often measured in the ways I have mentioned (there are likely other setups that I've not seen).  Small & medium sized indexing fixture components are readily commercially available, and can use collets, mandrels or chucks.  If the workpiece is large enough, hydraulically lifting one of the ends of the chucking fixture can easily achieve the inclination needed.

Guidance rails are commonly set up parallel to the surface plate, with the indicator moved along its length.  It's not a trivial setup perhaps, but it is not uncommon.  Granted, the error should (not must, should) be less than 10%, as with most setups.

As for #3, you seem to be looking at it strictly as a surface straightness indication.  If you leave the indicator in a single longitudinal position as you rotate the part (as you would for a circular runout), you are then verifying the surface with respect to the basic profile; as long as the indicator has been zeroed before starting, the deviation at any position along the surface must be within the surface profile zone.  You take readings progressively along length of the feature as the workpiece is being rotated.

By using any of the setups that I've described, in conjunction with a surface profile control, you effectively have an attribute go/no-go gage.

The term CMM encompasses contact and non-contact systems.  The majority of time I see them used is in automated mode rather than manually operated; the typical exception is one-offs or first-offs, where a program hasn't been established yet.  There are vision systems marketed for doing profiles of a rotated body, and I have used them to verify profile controls on a conical surface of great precision.

 

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

Jim:

Here is what I see.

The originator of this question wanted to make a functional gauge to check the runout on a tapered surface and wanted to know if the datum could use the modifier MMC. Well, it can't. Both circular and total runout are always in RFS.

You suggested a profile of a surface and is much more restrictive and could have a cost impact on the product. Is it easier to confirm than runout?? No, it isn't. Can it be done? Yes, it can.

Even in the new ASME Y14.5-2009 it states "it is even more important that the design more precisely state the functional requirements". Do we really need profile of a surface? Just imagine the originator of this thread suggesting we place profile of a surface on this taper and it has a cost impact of even $0.50 a part. One would need some strong background and I doubt there is one.

If I were the person making a decision on this design change, I would ask the person suggesting the change to tell me what the function of the feature and why circular runout cannot meet its functional needs. Why do we need profile of a surface? I hope all Designers think like this but I don't think it is happening out there.
 
 

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

Dave,
You are correct on the first point; then again, I never said any runout could be at MMC (control or datum), so I'm not sure why you're raising it again.

It does, however, confound me when people automatically assume that profile of a surface will cost more to verify than other controls.  Profile of a surface establishes a boundary within which the feature must be contained.  Is that not the same function as an attribute gage?  I understand that profile is not yet as widely understood as some of the other controls, however its versatility and general ease of verification are indisputable to those who understand and use it.  I use surface profile extensively when all that I am worried about is a boundary rather than separate and distinct size and location or orientation controls.  In every case, once the fabricator understood what a surface profile was, and how to verify it, the costs of the part dropped and the inspection was facilitated.  As a side bonus, if you hook up your indicator for electronic data acquisition, you would also get data for SPC.

I am curious how you would verify the size of the cone?  At one end?  Both ends?  With a +/- size tolerance, you only get size controls at locations where the size is specifically detailed; nothing in between.  What about the form (conicity for lack of a real term)? Rule #1 doesn't apply here because it's not a feature of size, so you can't use Taylor's Principle.  What is controlling the barrelling / waisting along the length?  Circular runout will control the straightness of the axis, but not tell you anything about the surface deviations along the conical feature.

Before the OP uses any GD&T suggestions from any source, they need to understand the design intent and the real impact of each type of control.  If the runout needs to be tighter, then put it as a refinement of the profile control.   

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

Jim:

If one converted a circular runout tolerance to a profile of a surface with the same value, the requirements are more stringent and the costs increase. Tighter tolerances cost more $$. This has nothing to do with the difficulty in confirming the profile tolerances or whether the part is automotive or not.

If the cone size/angle tolerance and the circular runout tolerance were combined, then I could see that there would not be a cost increase but I don't think that happens in real life.

The function and relationship of the cone determines whether a profile of a surface is more appropriate than circular runout.  

Dave D.
www.qmsi.ca

RE: MMC on Datums for Runout

Dave, please re-read my original post ... "Use profile of a surface where the limits are the equivalent inner boundary and outer boundary from your original combination of size & runout."  I was pretty clear that you don't just substitute one control for the other without doing some math.  Some designers may not understand how to do the math in some cases, but again, I can assure you that such conversions are done, and I've seen them done properly enough times to know that industry is doing it.

Your assertion that size & circular runout are adequate still doesn't address the questions I posed to you about the size controls between the cross sections with toleranced sizes, and the form effects along the length.  These aspects need to be controlled.  

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

Here's an alternative strategy that avoids the problems of circular runout and surface profile:

Specify Symmetry to control the orientation and location of the cone.  The datum features would be the two theoretical planes that are associated with the datum axis.  This would provide control in two perpendicular directions.  Because the conical surface is tilted, the opposed pair midpoints would have to be calculated normal to the basic angle of the cone.  I propose that this "radial symmetry of a cone" characteristic be named Cone-centricity.  Then refine the form and angular size of the cone by applying an Angularity tolerance to each linear surface element, with respect to the opposite surface element.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: MMC on Datums for Runout

Sorry, Evan.  I misunderstood your intent, so I've red-flagged my previous post to remove it.  

My concerns are;
1) Symmetry and concentricity require the averaging of directly opposed points to find the derived median plane or derived median line, which is then checked against the location wrt the datum axis or datum plane.
2) Both of these controls (concentricity and symmetry) and their datums apply RFS (5.12.1, 5.14); MMC and LMC aren't permitted as the controls are based on the actual surface rather than the MMC virtual surface, which would give you zero positional error upon inspection.
3) Symmetry applies to nominally planar surfaces and concentricity applies to nominally circular elements.
  - How will you determine which pair of planes to use?
  - How will you establish the planes?
     - A tangency modifier on the tolerance would establish a plane at max'm limit of the surface, however you would have an infinite number of opposed tangent planes around the circumference, so it would be time consuming to verify.
4) After establishing these line-element control zones for location, you propose to "refine the form and angular size of the cone by applying an Angularity tolerance to each linear surface element, with respect to the opposite surface element.  
  - Angularity within Y14.5 is a linear zone established at a basic angle from the datum, but if I understand this correctly, you are now defining each opposite line element as the datum, similar to putting "individually" on a datum feature callout.
  - Looking back at #3, you'd have an infinite number of such opposed line element datums.
  - As your datum has now changed, you'd need a new inspection setup at each rotational location.  
  - Form doesn't have any datum reference, so you'd have another setup for form, which appears to be the same as straightness along the surface if I understand you correctly. If that's the case, then you have to float the workpiece until you get the minimum straightness reading along the cone's length at each radial location.
5) I'm not sure how this new control would simplify the situation.

I'd still stick with surface profile, maybe even a composite surface profile if refinements of orientation & form are needed.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: MMC on Datums for Runout

Jim,

Ok, I'd better put a stop to this right now.  I don't think that either one of is sure whether or not the other is kidding anymore.  Other readers are probably confused as well.

My cone-centricity/angularity strategy was intended completely as a joke.  I had tried to make it so ridiculous that it wouldn't be taken seriously.  But I suppose that it didn't really sound much crazier than some of my other ideas that were intended as serious.

If you were trying to be nice and provide an earnest critique without inviscerating me, then I'm sorry.  I guess I'm not too good at conveying sarcasm and feigned indignation in a text form, and the intent wasn't clear.  If your comments were in jest, and the joke's on me, then I deserve it and that's fine.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: MMC on Datums for Runout

Nah, we're good.  I figured you were joking, but with your response I thought ... oh, he's actually serious?!  

As an instructor, I get to hear lots of "but that doesn't work for us, so why don't you nice standards people just do it this way instead, and have this mean that instead ... but only in this case 'cause we like the rest of the standard pretty much."  I had a student comment recently that it wasn't nice when I laughed openly at someone's suggestion for a universal customization to suit them.  It wasn't really a laugh, it was more of a chuckle because everyone thinks their issues are unique to their company and products.  I guess I should'a let them in on the joke too.  C'est la vie!  Live & learn.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

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