Composite or two single segments can be used with bidirectional tolerancing? 1

If I'm reading it all correctly, each hole will have to reference its own secondary datum (B for the LH hole, and C for the RH hole). Therefore, they are on different "playing fields" and would require two single segments, not composite.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

J-P,
Yes you are reading it correctly.
The reason we said composite or multi segments was to impose simultaneous requirements needed. --our intent was to add a note near the positional callouts---
Q1. How we can force sim req with two single segments?
Q2. Diametrical symbol is no needed for the position, but needed for perpendicularity? Am I right?
Q3. Each hole will have three callouts? ( two positions, one for W-E direction, one for N-S direction with no diametrical symbol and one perpendicularity to A with diametrical symbol). Does it make sense in gd and t language? Is the design intent clear this way or it's another better way?

If I am visualizing this correctly, following could work:

For the left hole:
|pos|dia. .030|A|B| (FCF #1)
|pos|dia. .005|A| (FCF #2)

For the right hole:
|pos|dia. .030|A|C| (FCF #3)
|pos|dia. .005|A| (FCF #4)

FCF #1 -- controls position of left hole in all directions;
FCF #2 -- tightens position of left hole in NORTH-SOUTH direction + controls perpendicularity of axis of the hole to datum axis A. WEST-EAST location is still controlled by FCF #1;
FCF #3 -- controls position of right hole in all directions;
FCF #4 -- tightens position of right hole in NORTH-SOUTH direction + controls perpendicularity of axis of the hole to datum axis A. WEST-EAST location is still controlled by FCF #3;
FCF #2 and FCF#4 - since these are single segment positional callouts related to the same datum feature, at the same material boundary condition, simultaneous requirement applies, so that the alignment (clocking) of the two holes is controlled.

There is also an option to go with bi-directional positional tolerancing to achieve different requirements for WEST-EAST vs. NORTH-SOUTH locations, but this would probably require view-dependent dimensioning to clearly define directions of rectangular positional tolerance zones. With my approach everything can be easily shown in one view, as far as I imagine.

I have two related questions to dive into this a little bit more:
1. Could the datum C callout be replaced with the datum B callout and still retain the same dimensioning scheme (right hole from right side) left hole from left side without affecting the meaning of the drawing?
2. The way I read it B and C establish datum planes at the end of the part and datum A establishes a datum axis down the center. Using tolerance scheme suggested by you, pmarc, I understand how the location of the holes is controlled in the N-S-E-W direction loosely by the first callout and then refined in the N-S direction by the second callout (I believe that it is also refines how much “tilt” off axis is allowed in the E-W and N-S?). My question is, I don’t see how the angular alignment (clocking) is controlled between the two features even though simultaneous requirements apply. Does one of the holes not have to be established as a datum feature itself with the other given a parallelism callout in order to control the “clock”?

Keith,
1. First of all, if C was replaced by B in positional callout for right hole, one of two things would have to happen. Either there would have to be a basic dimension from B to right hole defined (or from left hole to right hole), and as far as I understand OP there is no such dimension there, OR the length of the shaft would have to be basic (we do not know that from OP). These would define basic relationship between right hole and datum plane B on the drawing.

Secondly, even if the basic relationship was there, you would not end up with the very same geometrical requirements for the part by just switching C to B.

2. No, one of the holes does not have to be assigned as a datum feature for the other hole to control "clocking". If you have access to Y14.5-2009, look at figs. 4-40 and 4-41.

Pmarc,
What if we replace FCF2 and FCF4 with one single call-out saying “2X |pos dia .005|A|
Will that invoke Sim req-t as well?

Yes, SIM REQT will be invoked. However, if the holes are of different size, I would for clarity stay with initial idea.

"What if we replace FCF2 and FCF4 with one single call-out saying “2X |pos dia .005|A|"


So in CH scenario ("2x pos dia .005 to A) how the callouts would look like.


For the left hole:
|pos|dia. .030|A|B| (FCF #1)
2X |pos|dia. .005|A| (FCF #2)

For the right hole:
|pos|dia. .030|A|C| (FCF #3)

In this case I don't know that for the right hole the N-S location would be controlled to .030 or to .005 since does not have the lower segment. Can 2X on the lower segment cover the other end of the shaft?

Pmarc,
Didn't you have lenghtier explanation for Keith (I remember seeing something with tolerance accumulation and the necessity to have tighter tolerance .30 and 10). Or I am just seeing things?

greenimi,

I see no real advantage of method with 2X |pos|dia. .005|A|.

And yes, my answer to Keith was a bit longer, however I found my explanation muddy even to myself, so I red flagged it in order not to introduce too much confusion.

You don’t need the second lower segment.
If you don’t use DIA symbol your .030 only applies in direction of the dimension.
Since it’s not composite, your “lower segment” acts like it’s just separate FCF

I agree that pmarc’s datum scheme is the best in our case. No doubt about. Clear and simple.
Now, just for academic purpose (and since we have talked about this issue in other threads and have been concluded that the composite callout ”can” be used for single feature, even the standard intent was not to be used for single features), I am proposing the following datum scheme, and I would like to ask you if “my scheme” is having the same effects (I was trying, again, for educational purpose only, to come up with another / different composition to say exactly the same thing)
Pmarc’s scheme was:
For the left hole:
|pos|dia. .030|A|B| (FCF #1)
|pos|dia. .005|A| (FCF #2)

For the right hole:
|pos|dia. .030|A|C| (FCF #3)
|pos|dia. .005|A| (FCF #4)

Proposed scheme (don’t say looks more complicated, because sure it is). I just want to find out if it’s equivalent.

For the left hole:
Vertical dimension (N-S direction): |pos| .005 |A| -- no Ø symbol ----
Horizonatal dimension (W-E direction): will be composite position
Composite position: PLTZF: |pos| .030|A|B| - - no Ø symbol-
FRTZF: |pos| dia. .005 |A| - - with Ø symbol—
With SIM REQ. note added on the FRTZF segment

For the right hole:
Vertical dimension (N-S direction): |pos| .005 |A| -- no Ø symbol ----
Horizontal dimension (W-E direction): will be again composite position
composite position: PLTZF: |pos| .030|A|C| - - no Ø symbol-
FRTZF: |pos| dia. .005 |A| - - with Ø symbol—
With SIM REQ. note added on the FRTZF segment

This

CH,
That is your scheme. And I guess your scheme is fine too (with some debates about the real advantage of using your scheme)

I have posted a different one where I have used composite position, that one I am questioning.

"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
For the left hole:
Vertical dimension (N-S direction): |pos| .005 |A| -- no Ø symbol ----
Horizonatal dimension (W-E direction): will be composite position
Composite position: PLTZF: |pos| .030|A|B| - - no Ø symbol-
FRTZF: |pos| dia. .005 |A| - - with Ø symbol—
With SIM REQ. note added on the FRTZF segment

For the right hole:
Vertical dimension (N-S direction): |pos| .005 |A| -- no Ø symbol ----
Horizontal dimension (W-E direction): will be again composite position
composite position: PLTZF: |pos| .030|A|C| - - no Ø symbol-
FRTZF: |pos| dia. .005 |A| - - with Ø symbol—
With SIM REQ. note added on the FRTZF segment
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

I imagine this scheme, what do you think?
Yes, I know, it's just for fun, at this point....

greenimi,
My first question or two about your scheme would be:
What functional requirements force you to specify the tolerance zones rectangular (as defined by bi-directional positional callouts) and in the same time cylindrical (as defined by perpendicularity FCF)? Have the functional requirements been identified correctly?

Pmarc,
Fair enough. I know my datum scheme (or even CH’s scheme) does not have as much connection with “functional requirements” as the one you proposed. I just want to find another way to say exactly the same thing in GD and T language. My goal was to find some schemes which are just two different syntaxes to say exactly the same thing. Did I achieve my goal?

If you wanted to find a scheme resulting in exactly the same geometric requirements as my scheme, your proposal is different -- some of the tolerance zones in your scheme are rectangular, all of the tolerance zones in my scheme are cylindrical. That is the main difference.

Where was the composite can be used for a single feature debate?

"Where was the composite can be used for a single feature debate? "




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