Functional Datums - Advanced Concepts of GD&T 2nd edition by Alex K

[optomist1]

Hi To All,

If anyone has access to Advanced Concepts of GD&T 2nd edition by Alex K., I need clarification/help regarding figure 13-7, page 13-6 Chapter 13 Datum Systems Tolerance Stacks.

Specifically when calculating Max Distance X (A) and Min Distance X (A), I follow the calculation for Max Distance X (A); the basic dimension 15 less 1/2 of the hole MMC - tolerance of position (10.4 -0.2)/2 = 5.1; 15.0 - 5.1 = 9.9

However; calculating the Min Distance X (A) not so clear, rather foggy.
I get the 15 basic dimension, yet what is the rational for inclusion of the other numbers -10.6 and the +5.1???

The same can be said for calculating Max Distance X (B) & Min Distance X (B).

Any help navigating this key concept will be appreciated!!

Regards,
Marty

 

[Stijloor]

I am away from "the source", I'll take a look at it in a few days....

Happy 4th!!

Stijloor.

 

[optomist1]

Thanks you too....

 

[optomist1]

Hi To All,

If anyone has access to Advanced Concepts of GD&T 2nd edition by Alex K., I need clarification/help regarding figure 13-7, page 13-6 Chapter 13 Datum Systems Tolerance Stacks.

Specifically when calculating Max Distance X (A) and Min Distance X (A), I follow the calculation for Max Distance X (A); the basic dimension 15 less 1/2 of the hole MMC - tolerance of position (10.4 -0.2)/2 = 5.1; 15.0 - 5.1 = 9.9

However; calculating the Min Distance X (A) not so clear, rather foggy.
I get the 15 basic dimension, yet what is the rational for inclusion of the other numbers -10.6 and the +5.1???

The same can be said for calculating Max Distance X (B) & Min Distance X (B).

Any help navigating this key concept will be appreciated!!

Regards,
Marty

 

[Marc]

A quick "Bump" - Can anyone help with this one? My Thanks in advance.

optomist1: It may be that no one here has that specific book, but maybe someone can help with the concept.

 

[Stijloor]

A quick "Bump" - Can anyone help with this one? My Thanks in advance.

optomist1: It may be that no one here has that specific book, but maybe someone can help with the concept.

I do have the book, but because of other commitments, I have not had the chance to check this out...

Stijloor.

 

[David DeLong]

Hi To All,

If anyone has access to Advanced Concepts of GD&T 2nd edition by Alex K., I need clarification/help regarding figure 13-7, page 13-6 Chapter 13 Datum Systems Tolerance Stacks.

Specifically when calculating Max Distance X (A) and Min Distance X (A), I follow the calculation for Max Distance X (A); the basic dimension 15 less 1/2 of the hole MMC - tolerance of position (10.4 -0.2)/2 = 5.1; 15.0 - 5.1 = 9.9

However; calculating the Min Distance X (A) not so clear, rather foggy.
I get the 15 basic dimension, yet what is the rational for inclusion of the other numbers -10.6 and the +5.1???

The same can be said for calculating Max Distance X (B) & Min Distance X (B).

Any help navigating this key concept will be appreciated!!

Regards,
Marty

It would help if Marty could sketch up what he is talking about and post it here. I do not have the book but have a pretty good understanding of GD&T.

 

[optomist1]

Hi David,

Thanks for the response, I'll get a sketch together and post within the next day. Thank you again!

Regards,
Marty

 

[optomist1]

It would help if Marty could sketch up what he is talking about and post it here. I do not have the book but have a pretty good understanding of GD&T.

Good Morning David,

Attached is a scanned version of the problem; I am trying to get it straight, regarding how or the steps to calculate the max and min distances on the attached sheet. It is my understanding that this procedure should be applied consistently. If I am off base set me straight. This is an exercise to demonstrate that changing the tolerance of position/datum call out and Datums/sequence to suit manufacturin/inspection results in tighter tolerances. I get the Max. calc., but I do not follow the Min Distance calculation for version (A) or (B).

Many thanks for your assistance....

Regards,
Marty

 

[David DeLong]

Good Morning David,

Attached is a scanned version of the problem; I am trying to get it straight, regarding how or the steps to calculate the max and min distances on the attached sheet. It is my understanding that this procedure should be applied consistently. If I am off base set me straight. This is an exercise to demonstrate that changing the tolerance of position/datum call out and Datums/sequence to suit manufacturin/inspection results in tighter tolerances. I get the Max. calc., but I do not follow the Min Distance calculation for version (A) or (B).

Many thanks for your assistance....

Regards,
Marty

The pic certainly helps out a bit.

Think of the dark circle as your pin which is the virtual condition size (10.4 ID which is MMC - 0.2 tolerance) of 10.2 diameter. The feature of size which is a hole cannot protrude beyond this diameter located at 15 mm from datum D.

Maximum distance - In the first example, the part has shifted down to the maximum distance so that the 10.2 pin is touching the top side of the hole. The minimum distance is 15 (basic) - 1/2 the pin size or 1/2 the virtual condition size (10.2/2) = 5.1. So 15 - 5.1 = 9.9 distance.

Minimum distance - in the second example, the gauge pin touches on the bottom side of the hole. Making this hole at its largest size will give us the minimum distance.

The largest hole allowed is 10.6 mm ID. The virtual condition or pin size is 10.2 mm which give us difference of 0.4 mm. The minimum size would then be 15 - 1/2 pin size - 0.4 (difference in diameters) = 15 - 5.1 - 0.4 = 9.5 mm.

This corresponds to the answers in the book.

Hope it helps.