MISC GD&T PROFILE QUESTION

[[Ma...]]

There has been a conversation with a vendor of ours regarding the evaluation of this profile. I'm wondering how the smart people of this forum would interpret this drawing. Much like a lot of drawings from this customer there are a lot of back and forth regarding the design intent. Unfortunately, we don't have access to their end customer to find out what they'd like on these parts so it's a back and forth between my company and the "middleman" vendor. I attached a (poorly done) sketch of the drawing. It's to ASME Y 14.5. The question is how would you interpret this profile to A & B with both having modifiers? Modifiers on profiles always confused me to begin with and I'm genuinely curious. One party believes that the profile is to A and B with additional tolerance generated from the features of size. The other party is of the thought that the .400 basic while aligned to plane B is how the part should be evaluated and no modifiers applied. I'm just an innocent bystander on this one (thank God), but we've had several of these differences as a company between this customer and out of curiosity I'd like to know how you guys would interpret the call-out. I think I provided all necessary information from the drawing, but if there's more information I can provide, let me know. 

[[Da...]]

I deal with this a lot myself (in fact, the other post I have about the program which will not measure my last diameter is one), and when it comes to datum shifts on secondary and tertiary datums, I just let the software deal with it. If I measure it by my TesaHite or my Mistral manual CMM, I just leave it at RFS.

Theoretically, you COULD trig it out on paper, but then this isn't a pre-calculus class homework problem and "ain't nobody got time fo' that"!

[[Ro...]]

Profile of surface does not get modifiers.

Source, dirty old poster on my wall

 

 

[[To...]]

Found this in 2009. Full disclosure, there was no examples in the Profiles section.  Just this paragraph.  4-39 appears to be tied to the position.

 

Edited January 21

[[Cl...]]

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The datums can.

[[Cl...]]

The Y14.5 Standard tells us that we cannot apply the MMC modifier to a profile tolerance because it is a surface control. We can, however, apply MMC or LMC to the datum references of a profile tolerance where the datum features are features of size.

[[Je...]]

Datum references do not get material condition modifiers, they get material boundary modifiers.  MMB/LMB absolutely are applicable to Profile of a Line and Profile of a Surface requirements.

The MMB modifiers allow for "shift" but not "bonus" tolerance applied 1:1 as MMC/LMC works traditionally.

Based on the presented drawing, this isn't a "debatable" topic.  Its clearly defined and if there are debates around this with your company and your customer, it would behoove you (read:your company) to take some basic & advanced GD&T courses (I'll shamelessly plug AGI here).  I can confidently state that it will save you 10x more than the cost of the courses.

[[Je...]]

Mark,

It sounds like you are faced with a challenging situation in not having access to the end customer but needing to understand their drawing. Great job on looking to peers on this forum for help.

When a circled "M" is placed next to datums in a feature control frame, it is referred to as Maximum Material Boundary (MMB), which enables Datum Shift for datum features of size. While MMC (Maximum Material Condition) applies to the feature being toleranced, MMB (Maximum Material Boundary) is used to describe the boundary of the datum feature during datum shift. These two ideas are commonly confused.

Datum shift does not add bonus tolerance to the controlled feature's stated tolerance, so the .004 profile tolerance is constant.

Datum shift refers to the allowable movement of a datum feature simulator (datum mobility). Datum shift is commonly used in composite position tolerancing to provide flexibility in aligning datum simulators within allowable boundaries. It is equally valid for profile characteristics, where it enables greater manufacturability. While MMC is not permitted on profile characteristics, MMB is perfectly legal and is a great tool for ensuring functional alignment without over-constraining the part.

In metrology software such as Calypso, the allowable movement (datum shift) is calculated mathematically using the MMB defined by the material modifier. You can enable datum shift within a characteristic setup in Calypso, where applicable.

I hope this helps, and keep us posted on how this turns out.
 

Here are some places in the ASME Y14.5-2009 standard to read more about datum shift:

Section 4.4.3 (p. 56)

Section 4.11.7 (p. 82)

Edited January 23

[[Da...]]

While we are talking about 'datum shifts', I have a minor issue with a part I'm checking. Please look at the 2 holes below, from another post I had earlier:

On this part, you can see 2 flat-ish surfaces, the upper features which are all on the A-datum, and the features on the lower lever which are on the D-datum. Each alignment is a Plane-hole-hole alignment, with the E-datum on the lower level measured to ØE(rfs), D|B(mmc)|C(mmc), and the F-datum measured to ØF(rfs), D|E(mmc)|C(mmc). Aside from the transitional datums, all other holes are measured to Ørfs, Primary|Secondary(mmc)_Tertiary(mmc). OK, those are all the possible datum structures on this part.

Now, when I go to measure these 2 side-hole, through a surface which is perpendicular (at least to a ±1° tolerance) to each primary datum, A and D. But these holes are independently dimensioned Ø (rfs), A|B(mmc)|C(mmc), which already raises 'concerns' for myself. Neither hole actually is on a primary datum, and referring to mmc on datums on a perpendicular surface leaves me confused as to just how such a shift could be assumed. I realise that the datum shift done properly creates a 2-dimensional 'plane of possibility' for location of each datum, but measuring the same from a perpendicular direction leaves you now with only a 1-dimensional 'line of possibility' for location, which I think might be possible?

Well, Calypso will measure it in the A|B|C alignment, but will not accept any datum modifier on either of these 3 holes. No big deal; the parts still pass, but I wonder if this is because Calypso just was never programmed for calculating this, can't be programmed for calculating this, or if this callout is improper, won't calculate this (yet, somehow, will check it RFS)? 

[[Ma...]]

Sorry, but i have problems with understanding your setup ( what is what on image )

[[Da...]]

[[Ma...]]

And E, F are side holes? Or they are B, C? I am still missing necessary info to be able to create demo program or tell why it's not working.

[[Je...]]

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Hi David.

Thanks for asking about this.  Calypso is adept at calculating datum shift for position characteristics.

Like Martin, I'm a bit confused as to the actual print characteristic you are trying to evaluate.  You mention planar Datum A serving as primary, followed by B as secondary and C as tertiary, but then you also mentioned something about a Datum Reference Frame ØE(rfs) D|B(mmc)|C(mmc).

Which datum reference frame is used for this characteristic?

Also, the controlled feature does not need to be coplanar with the primary datum in a position characteristic.  The purpose of a primary datum is to establish the feature that serves as the primary reference and constrains the maximum number of degrees of freedom.

I've found that the new GD&T engine works well with position and datum shift.  There probably is a way to resolve your current problem using the legacy position characteristic, but it's worth giving the new version a shot as well.

Keep us posted.

[[Da...]]

Let me clarify: Datums A and D are primaries, datum B and E are secondary, datums C and F are tertiary. Both primary (A,E) datums are (X,Y) planes, secondaries (B,E) are (X,Y) origin holes,  and tertiaries (C, E)  are X+ directional rotation element holes. This is all on 1 formed sheet of copper sheet, approx. 1.5mm thick.

These 'side holes' are on neither primary datum (A or D), but are on the formed side between the datums, nominally 90° in the Y axis from either datum A or D, on what in this case would be a (Y,Z) plane which is NOT defined as a primary datum. So essentially, these 2 holes are positioned to a datum structure  (A|B|C) they are perpendicular to. 

 

[[Ma...]]

Can you be more specific? Draw or use better description which hole is which datum.

I've used: plane A circle(M) on A and circle(M) on D for reporting only X ( with using special rotation ) of one of side circle.
For that i recalled side circle as point to be able to use MMB on datum circles.

[[Da...]]

I'm going to put in my thoughts...

Datums A and D are parallel to the side holes and would provide the distance for the horizontal centerline of the side holes

Datums B and E are holes through A and D and would provide the distance for the vertical centerline of the side holes

Datums C and F are holes through the A and D planes and provide rotation for the datum structure.

What is the confusion about?

[[Ma...]]

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Did you just named holes through A and D twice with another name??? Are they B and E or C and F?

[[Da...]]

He said the datums were plane, hole, hole. Looking at his picture datums A and D are planes. A is the upper and D is the lower. B and E, as well as C and F are holes.

Please correct me if I am wrong.

[[Ma...]]

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Until author will tell us what is what, then we can not help.

There is TP callout for two holes and both have same datums except primary one. And i can not tell which are datums and which are for TP report.

[[Da...]]

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Edited Tuesday at 04:35 PM

[[Da...]]

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You are correct.

The way I read this callout is the following:

     a) Location of these holes are dimensioned in the X-axis according to the ABC alignment, but

     b) in the Y-axis solely by the depth at which I measure the circular measurement of the hole, and

     c) not at all in the Z-axis (which I really don't think is what they want, but we are 2 layers below the final customer, and our intermediate customer's QC people don't understand ASMY Y14.5 very well...).

While I feel that this design-customer callout is in error, I'm just trying to placate our customer (the intermediate vendor), and am attempting to actually incorporate the datum shifts on the callout, but Calypso won't allow it on just these 2 holes.

Edited Tuesday at 04:46 PM

[[Da...]]

The horizontal centerline of the circles is parallel to datums A and D. The vertical centerline is perpendicular but will get it's position from B and E. Positionally the center of the circles has a distance from A/D and one from B/E. C/F control rotation. Calypso will only apply the datum shift as needed. Perhaps I am looking at this wrong so let me ask a couple of questions about your set up. Is the A plane in Z+ ? Are the 2 side holes in Y- ? You stated that the circles are called out to A|B|C so is it ok if I don't use D|E|F ?

[[Da...]]

Yes, the datumA plane is  Z+, as are the normal vectors of all holes EXCEPT these side holes, which have normal vectors of Y-. Side holes are called out as     |Ø10mm +.1/-.2 |A|Bmmc|Cmmc|

[[Da...]]

Thank you. Since these are through holes the Y does not apply for position. Y would apply to the face at the bottom of the counterbore. Z comes from datum A and X comes from datum B. Calypso would only use the mmb if it was needed. Do you also get mmc for these side holes?

[[Ma...]]

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Tried this approach? For Z TP will MMB have no effect if it's used on circles from plane A and D