## Stackup RFS-MMC combo, simple part, same results?

## Stackup RFS-MMC combo, simple part, same results?

2

aniiben (Mechanical)
(OP)

I’ve studied a bit the stackup calculations presented on eng-tips, especially the ones where a “simple” OD-ID relationship is shown (a.k.a. ID = datum feature and OD = controlled feature)

For the feature control frames that have only RFS and MMC/MMB modifiers, am I safe to conclude that the X max and X min calculation RESULTS are the same regardless of how the modifiers/ or lack thereof are shown?

In other words:

position RFS to datum RFS

position MMC to datum RFS

position MMC to datum MMC/MMB

position RFS to datum MMC/MMB

will give the same results for the maximum / minimum wall calculations ?

Is this true? Yes, no, maybe ?

At least look like that might be the case unless I am missing something.

For reference one relevant thread, but extended to my questions above

http://www.eng-tips.com/viewthread.cfm?qid=426288

For the feature control frames that have only RFS and MMC/MMB modifiers, am I safe to conclude that the X max and X min calculation RESULTS are the same regardless of how the modifiers/ or lack thereof are shown?

In other words:

position RFS to datum RFS

position MMC to datum RFS

position MMC to datum MMC/MMB

position RFS to datum MMC/MMB

will give the same results for the maximum / minimum wall calculations ?

Is this true? Yes, no, maybe ?

At least look like that might be the case unless I am missing something.

For reference one relevant thread, but extended to my questions above

http://www.eng-tips.com/viewthread.cfm?qid=426288

## RE: Stackup RFS-MMC combo, simple part, same results?

Not sure what exactly makes you think that all these four different combinations, that is:

1. position RFS to datum RFS

2. position MMC to datum RFS

3. position MMC to datum MMC/MMB

4. position RFS to datum MMC/MMB

always give the same results for min and max wall thickness calculations, but I don't think this is true statement.

## RE: Stackup RFS-MMC combo, simple part, same results?

ID: 20 ± 0.5 — datum feature A

OD: 50 ±1.3,

position Ø3 -case 1, 2, 3 or 4

1. position RFS to datum RFS

2. position MMC to datum RFS

3. position MMC to datum MMC/MMB

4. position RFS to datum MMC/MMB

I got 10.8 for minimum and 17.4 for maximum not matter what!

Which case do you think DOES NOT fit the pattern?

## RE: Stackup RFS-MMC combo, simple part, same results?

Thank you.

## RE: Stackup RFS-MMC combo, simple part, same results?

## RE: Stackup RFS-MMC combo, simple part, same results?

On the other hand, think of the idea of bonus tolerance - as hole is getting larger, it can be moved further away from theoretical position for exactly the same amount, so bonus tolerance does not affect wall thickness.

Hence no difference between MMC (bonus tolerance) and RFS (no bonus tolerance)

"For every expert there is an equal and opposite expert"Arthur C. Clarke

Profiles of the future## RE: Stackup RFS-MMC combo, simple part, same results?

Looks like when RFS and MMC modifiers are invoked there would be no difference between the callouts, hence min. / max. results are the same.

What about when LMC/ LMB modifier is used in combination with RFS or MMC/MMB?

I would expect:

5. position MMC to datum LMC/LMB AND

6. position RFS to datum LMC/LMB

to get the same min./max. values

Also

7. position LMC to datum MMC/MMB

8. position LMC to datum RFS (12.1 / 18.7)

to be the same

However, I find that was not the case. Either, I am doing (conceptually)something wrong or what I expected is not realistically true and the analogy does not work (for some reasons that I am not aware). I was able to get “verifiable (on this forum)” results only for case#8 == values shown==

## RE: Stackup RFS-MMC combo, simple part, same results?

Thank you

ANI

5. position MMC to datum LMC/LMB (x min=10.8, X Max.= 17.4)

6. position RFS to datum LMC/LMB (x min=12.1, X Max.= 18.4)

7. position LMC to datum MMC/MMB (x min=12.1, X Max.= 18.7)

8. position LMC to datum RFS (x min=12.1, X Max.= 18.7)

## RE: Stackup RFS-MMC combo, simple part, same results?

Interesting thread.

I am not able to get the same numbers.

Could somone, please, confirm that shown values are the correct ones. I am trying to learn from this kind of stacks.

Thank you

## RE: Stackup RFS-MMC combo, simple part, same results?

I did it, but unfortulately, due to my lack of knowledge/abilities I got different results.

5. position MMC to datum LMC/LMB

~~(x min=10.8, X Max.= 17.4)~~(x min=12.1, X Max.= 15.9)6. position RFS to datum LMC/LMB

~~(x min=12.1, X Max.= 18.4)~~(x min=12.1, X Max.= 17.4)7. position LMC to datum MMC/MMB

~~(x min=12.1, X Max.= 18.7)~~(x min=12.1, X Max.= 20.0)8. position LMC to datum RFS (x min=12.1, X Max.= 18.7) --ONLY THIS IS THE SAME---shame of me:(

Who is right? What are the coorect values?