Runout referenced with a datum of pattern of holes
Runout referenced with a datum of pattern of holes
(OP)
Hi All,
Recently I saw a drawing where the runout control is referenced with axis of pattern of holes as the datum. I doubt whether it is a legal specification for runout?
Please see the attached drawing.
The four holes dia 10-11 are the clearance holes, the disk will be mounted to a spinning part using the fasterners.
I understood that dia 9.8 gauge pins located on a PCD of 100mm can be used to varify the position of the 4 holes. Also I understood that using M modifier is a must when we use pattern of holes as a datum. I have no doubt on this.
The question is, the outer diameter of the disk is controlled with respect to the 4 hole pattern using runout , How is this possible?
because the datum B is the axis derived from the pattern of 4 fixed gauge pins of size 9.8. How to simulate the datum B here? will there not be any play between the holes and the datum simulator? obviously there will be a play - How to measure runout for this.
Can any one help me to understand this doubt.
Recently I saw a drawing where the runout control is referenced with axis of pattern of holes as the datum. I doubt whether it is a legal specification for runout?
Please see the attached drawing.
The four holes dia 10-11 are the clearance holes, the disk will be mounted to a spinning part using the fasterners.
I understood that dia 9.8 gauge pins located on a PCD of 100mm can be used to varify the position of the 4 holes. Also I understood that using M modifier is a must when we use pattern of holes as a datum. I have no doubt on this.
The question is, the outer diameter of the disk is controlled with respect to the 4 hole pattern using runout , How is this possible?
because the datum B is the axis derived from the pattern of 4 fixed gauge pins of size 9.8. How to simulate the datum B here? will there not be any play between the holes and the datum simulator? obviously there will be a play - How to measure runout for this.
Can any one help me to understand this doubt.





RE: Runout referenced with a datum of pattern of holes
RE: Runout referenced with a datum of pattern of holes
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RE: Runout referenced with a datum of pattern of holes
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Runout referenced with a datum of pattern of holes
That drawing is flat wrong.
9.3.1 Datum Feature for Runout Tolerances (page 180 ASME Y14.5-2009) states "The datum axis for a runout tolerance may be established by a cylindrical datum feature of sufficient length, two or more cylindrical datum features having sufficient axial separation or a cylindrical datum feature and a face at right angles to it."
I think the use of positional tolerances would be more appropriate on this drawing.
Dave D.
www.qmsi.ca
RE: Runout referenced with a datum of pattern of holes
you mean to say, we have to use a variable gauge pins but the center of which has to be exactly located on its true position (PCD basic 100 and 90 deg apart as shown in drawing.
I was under impression that, whenever we use a patten of holes as datum - even at RFS it has to be simulated with a fixed gauge. because the datum here is the axis derived from the pattern-not from individual holes.
In that case, assume we have 10 holes (or even more) insted of 4 holes, then do we need to use gauge pins for all the 10 holes? I hope we can choose some 3 - 4 holes in that case, does all the hol surface have to be in contact with the gauage pins- I think it does not require.
Please correct me if I understood wrong.
RE: Runout referenced with a datum of pattern of holes
I saw this drawing in " Tolerance stackup analysis by james meadows" chapter- stackup analysis for 5 part assembly.
RE: Runout referenced with a datum of pattern of holes
I think we can use position as you suggested. I to beleive the example i have posted is illegal specification, as dave quoted on selection of datums.
"9.3.1 Datum Feature for Runout Tolerances (page 180 ASME Y14.5-2009) states "The datum axis for a runout tolerance may be established by a cylindrical datum feature of sufficient length, two or more cylindrical datum features having sufficient axial separation or a cylindrical datum feature and a face at right angles to it."
RE: Runout referenced with a datum of pattern of holes
That said, I do see the intent. We can certainly envision something mounted on those 4 holes and then rotating, and then we may be concerned about the wobble.
But that specific usage is not in line with ASME.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Runout referenced with a datum of pattern of holes
If '94 is invoked, then you can't remove the MMC from the position control. If '09 is invoked, then I'd suggest doing away with the MMC on the position control and then you'd be ok. As for reasons to do this, it seems to me that the outer cylinder is being controlled wrt the center of the pattern; I have seen a need for something like this when you don't want too much overhang on mating pieces when centered up. Not a great way to do it, but achievable.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Runout referenced with a datum of pattern of holes
Assuming the "intent" is correct, would labeling the 4X Ø10.5 holes individually as datum targets satisfy the requirements?
What would be needed to make the 4 hole pattern fall under the criteria of "two or more cylindrical datum features having sufficient axial separation" ?
Joe
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RE: Runout referenced with a datum of pattern of holes
Sorry but the holes need to be in alignment creating the axis. Stick with positional.
Dave D.
www.qmsi.ca
RE: Runout referenced with a datum of pattern of holes
The standard sais "may be established", not "should", not to mention "shall".
So your choices are not limited to "two or more cylindrical datum features having sufficient axial separation"
RE: Runout referenced with a datum of pattern of holes
So If '94 is invoked, then you could indeed remove the MMC from the position control. But we still have the difficulty of establishing that pattern RMB when you get up to the runout tolerance...
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Runout referenced with a datum of pattern of holes
An ongoing issue of terminology may be at issue here again. In "voluntary standards" (i.e. not mandated by law), terms like "must", "will", "shall", etc. that are EXPLICIT and RESTRICTIVE are generally avoided because they preclude all other options. Their use can open a large can of legal worms for the document creators and publishers. Seemingly wishy-washy / open words like "may", are used in their place. To me, this is a real issue because it allows significantly different interpretations and "reading into" of the standards.
The certification exam treats this particular item as a "must" (i.e. features must be at MMC for the simulator).
Don't agree with Dave re the axes having to be aligned. That's contrary to 4.5.8.
Joe, if you really want the outside cylinder to be located wrt the pattern of 4 holes, and cylindrical, you can go with position and a cylindricityh control (expensive), but I would probably invoke Y14.5-2009 for that particular feature and drop the MMC from the FCF. Need to consider though if the extra restriction on the perpendicularity and inter-feature position of the 4 holes is necessary or too restrictive.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Runout referenced with a datum of pattern of holes
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Runout to something that isn't cylinder.
Now, after 14.5 2009 being around for a while the idea of complex feature as a datum doesn't look so crazy.
What if we consider holes all together as "irregular shape feature" and create setup similar to Fig. 4-35 in ASME 14.5 2009?
RE: Runout referenced with a datum of pattern of holes
Nice to see that you are back.
See that you are using the 94 standard referencing 4.5.8 and it is true that a pattern of holes can be a datum. No doubt about that.
Now lets get to either circular or total runout using the 94 standard.
6.7.1.1 page 189 of the 94 standard Basis of Control - The datum axis is established by a diameter of sufficient length, two diameters having sufficient axial separation, or a diameter with a face at right angles to it." There is no mention of a pattern of holes used as a datum.
Yeah, they have to aligned.
Dave D.
www.qmsi.ca
RE: Runout referenced with a datum of pattern of holes
I've heard stories / rumors that the requirement to specify the pattern of FOS at MMC was to allow / require hard-gauging because nobody knew how to finitely measure and verify. Don't know if that's true or not. If so, it makes sense that they would have precluded a pattern of features as a datum axis for runout controls. Doesn't seem so difficult today to use a pattern at RFS (RMB), but who knows.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Runout referenced with a datum of pattern of holes
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Runout referenced with a datum of pattern of holes
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Runout referenced with a datum of pattern of holes
I am becoming a bigger proponent of the "extended principles" idea over that of the black & white viewpoint. This isn't because of a fundamental change in my thoughts about following rules, but rather because the more we discuss stuff here, the more I find some subtle inconsistencies, not just a lack-of-example situations.
Certainly, if ASME explicitly mandates or prohibits something, then that should be followed. But aren't there times when that might tie our hands in other areas?
Case in point: despite the standard "recommending" certain datum features for runout (para. 9.3.1), I do see the benefit of having a pattern of holes as a datum for runout. The problem is that the standard clearly requires the datum references to be RMB.
From the other thread it sounds like ISO tries to nail down more loose ends while still allowing flexibility. Either way, there are always going to be gray areas where contradictions come to light, in both standards.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Runout referenced with a datum of pattern of holes
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Runout referenced with a datum of pattern of holes
By going through the above posts I got one more doubt, I think I can better post that in the new thread.