Composite Position Tolerance Simultaneous Patterns 2

[jeballes]

I've got a cylindrical part with two patterns of notches around both ends. I'd like to position both of them as one pattern, but have the two patterns controlled by separate feature-related tolerances. If I tolerance them as shown in the attached drawing, will the PLTZF for both patterns be set at the same time by the simultaneous requirements rule? Or does that only apply to the datum reference frame?

 

[greenimi]

Simultaneous requirement is implied for the upper segment (PLTZF) by definition, but not for the lower segment (FRTZF). In order to have simultaneous requirement for the lower segment too, you need to write SIM REQT under the feature control frame (lower segment) on both FCF's.

 

[greenimi]

And one more small detail: you do not need B as secondary in the lower segment (FRTZF). Does not bring anything to the callout. Does not stop any degrees of freedom. A primary, on both FCF's will do the job with SIM REQT per the above comment.

 

[jeballes]

So would I be correct in saying that the max clocking offset between a slot in one pattern and a slot in the other pattern would be the sum of the FRTZF tolerances divided by two (so .0075)? Vs. the sum of the PLTZF tolerances divided by 2 (.015) if SEP REQT were specified?

 

[greenimi]

My opinion, (and I know are some experts here on the forum than can chime in and correct me if I am worong) is that regardless if you put SIM REQT under FRTZF's (on both FCF's) the lower segment will control only the pattern orientation and not its location. Therefore, I would say the maximum clocking is still determined by the upper segment (PLTZF)

FRTZF will control the location of the slots within the pattern -location to each other but within its respective pattern---

What are the true-correct- functional requirements of those two slot patterns? How far they can be located from each other? What about how far they can be oriented from each other?

 

[jeballes]

The 4 slot pattern features can be located .010 from each other, but the 6 slot pattern features can only be located .005 from each other. The four slot pattern cannot be clocked more than .0075 from the 6 slot pattern. Clocking to datum -C- is not critical.

I've attached a view showing the PLTZF in blue, which will be the same for both, and the FRTZF in red. If this particular case is true, then the two patterns could be clocked a total of .015 from each other, which will not work for me. Thinking about how functional gaging would work for this tolerance scheme, it seems like this interpretation is correct. I would appreciate suggestions for any alternative approaches.

 

[greenimi]

Quote: "The 4 slot pattern features can be located .010 from each other, but the 6 slot pattern features can only be located .005 from each other. The four slot pattern cannot be clocked more than .0075 from the 6 slot pattern"

Based on this I do not think you even need the second / lower segment on both FCF's.
Just the uppper segment (PLTZF) will do the job.

Anyone else on the forum? Different opinion?

 

[SeasonLee]

Its not to answer OP’s questions, I’m thinking on simplifying the DRF by deleting the tertiary datum on both sides notch pattern FCF callout (upper segment POS|.015|A|B|), so the patterns are still located and related to common datum features referenced in the same order of precedence and at the same material condition, it still meet the simultaneous requirements, the notch pattern on both sides will be controlled at the same time.

If you know the application of simultaneous requirements, you may consider deleting the tertiary datum from FCF callout on the upper segment. Besides, I will recommend adding material condition (circle M) on the secondary datum B, it will be easier for gage making.

Season

 

[AndrewTT]

I would argue that the datum B in the lower segment of the composite position FCF does add something to the control of the feature. It stops the centerline of the slot from changing orientation wrt Datum B. Without having B in the lower segment the FRTZF could orient itself cockeyed inside the PLTZF (see attached).

As pointed out by SeasonLee if you are going to use a functional gage then you should consider adding the MMC modifier and the MMB modifier if your design intent can allow for the additional tolerance.

Keep in mind that you will need two gages for a composite FCF. One for the upper segment and one for the lower segment. If you think about how you would like to gage this part then the GD&T scheme may sort itself out for you. Also, without the "SIM REQT" note on the lower segments you would need a gage for each lower segment of the composite FCFs. So currently you are looking at 3 gages. Gage 1 covers the upper segment of both composite FCFs (SIM REQT rule is in play). Gage 2 covers the lower segment of the 4 slot pattern (SIM REQT not in play). gage 3 covers the lower segment of the 6 slot pattern (SIM REQT not in play).

As far as the "tolerance stack" of the two patterns wtr to "alignment" to each other, each pattern can use the lower segment tolerance all in orientation error. So one pattern could orient in one direction/manner and the other pattern could orient in the other direction/manner. I would lay this out in 2D CAD to convince myself that I fully understood how the values of the tolerance zones affected how much mis-alignment could occur. Take into account the tolerance on the depth of the slots also.

I would recommend looking at the following figures from 2009.
4-40 vs 4-41
7-30 thru 7-33
7-40 vs 7-47

 

[greenimi]

AndrewTT,

What degrees of freedom B would stop?

 

[AndrewTT]

B in the lower segment would arrest orientation with respect to datum B - 1 degree of freedom.

 

[greenimi]

Orientation is not a degree of freedom: translation or rotation are!

So, please try again.

 

[greenimi]

AndrewTT,
I know you are certified. I know you can do better than your last post!

 

[Belanger]

Geez, greenimi, you're picky

 

[SeasonLee]

We are not quite sure on the design intent of datum feature C, but from what I read on the OP sketch, there is a certain relationship on the two sides notch pattern, so I think the meaning will be different if we put the note SIM REQT on the drawing.

Season

 

[jeballes]

Thinking in terms of physical gages, I believe using SIM REQT on the FRTZF segments would satisfy design intent. Using one gauge to check the FRTZF would mean the patterns would have to be clocked to datum C together. If they weren't they'd pass the PLTZF check, but not the FRTZF check.

 

[greenimi]

Any other opinions on what B as a secondary in FRTZF is doing? What would be its value?

 

[powerhound]

Looks like B is refining the parallelism of the centerplane of the cutout to datum axis B to within .010. Is that not what it's doing?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[greenimi]

John,
I am asking in terms of degrees of freedom.

 

[greenimi]

Or in other words what the tolerance zones can do with and without B in FRTZF?