Axis to Axis calculation 2

[Gopinath K]

Hi
can any one help on this attached axis to axis shift calculations ?
i am aware virtual condition and resultant conditions but i had confusion on applying datum shift add or subtract ?
long back i worked on stack up method now after a gap i had confused,
please let me your ease way of calculations like any other method apart from stack up.

 

[3DDave]

 

[pmarc]

Gopinath K,
You should take a look at figs. 5-48 through 5-50 in ASME Y14.5M-1994. They should easily let you figure out the correct answers for cases A, B, C and E.

Case D is a bit different. There is the same amount of bonus tolerance as in cases A and B, but for the datum shift calculation you should keep in mind that the LMB size of datum feature A is 11.8, not 11.9 as it would seem at first glance.

 

[Garland23]

A star to pmarc for the hint about LMB. I had to ponder this for a few minutes before recalling that perfect form is not required at LMC.

 

[greenimi]

Garland23 (Mechanical)29 Jul 23 15:41
A star to pmarc for the hint about LMB. I had to ponder this for a few minutes before recalling that perfect form is not required at LMC

For case D

I agree. It is not required for the datum feature (A)
But it is required (perfect form at LMC) for the concerned/controlled feature diameter Ø24.

 

[SeasonLee]

the LMB size of datum feature A is 11.8, not 11.9

Would you please kindly interpret how to get this LMB size.
Thanks

Season

 

[greenimi]

SeasonLee,

How would you calculate the red dimension ?
Isn't it: 20.0-0.1 = 19.9.
I think that would be LMB

 

[SeasonLee]

Take Fig. 5-7 as an example, may I consider LMB as shown below, since the form variation 0.1 will happened on both sides.

Edit: LMB could not be a correct term, its not a datum feature here.
Please correct me if I am wrong on this concept.

Season

 

[greenimi]

Edit: LMB could not be a correct term, its not a datum feature here.

Why? Why in the case D (as mentioned by pmarc in his post and also mentioned by me in my post) feature A is not a datum feature?
I am very confused by your latest replay.
"A" is modified at LMB and it is datum feature for the case D position |Ø T(L)|A(L)|

I am sure I am the one not understanding your point, so I would like some clarifications.

 

[SeasonLee]

greenimi

For case D, LMB is a right term for sure. What I said LMB could not ne a correct term means the Figure 5-7 you posted.
Thanks to the Figure 5-7, it gives me a hint to think about LMB size.

Season

 

[Gopinath K]

Thank you all for your valuable discussion.

for case D
for the datum shift calculation LMB size of datum feature A is 11.8, instead of 11.9 is it because of Datum feature size tolerance ?
for example if datum feature size is dia 12 +0 -0.5, then does LMB is 11 ?
please conclude

 

[SeasonLee]

for example if datum feature size is dia 12 +0 -0.5, then does LMB is 11 ?

I will say yes based on my knowledge.

Here is the summaries of the max allowable distance between axes for all cases, as pmarc mentioned Case D is a bit different, and its really a bit difficult fo me to calculate the max allowable distance between axes, hope you guys will help me to fill it up, attached is an Excel file, it will be easy to edit. Thanks for your assists.
Again, as usual I said, please correct me if I am wrong.

Season

 

[SeasonLee]

File attached.

Season

 

[flash3780]

I cannot think of any reason to use an LMB modifier on a datum in the real world.

I think that I burned out a few brain cells trying to understand pmarc's comment that the LMB is less than the minimum diameter.

It makes sense, but sheesh! I would have missed that in a tolerance stackup for sure.

 

[pmarc]

SeasonLee,

This is the table for case D:

 

[3DDave]

By supplying these results rather than showing the subject at hand - the geometric relationship - the topic is completely obscured. Show the geometric basis and the calculation is obvious. Show the calculation results, particularly without the formulas, and it's a slight-of-hand, fun to watch and not so informative.

Also, Season Lee's example appears to have a non-URL character in it making it not down-loadable.

 

[SeasonLee]

pmarc
Thank you so much for the data on Case D, it’s really difficult for me to figure out how to get these data, it will be of great help to us, if there is a further interpretation. Thanks again for your assists in advance.

3DDave
Sorry for the link, I didn't notice that.

Edit: File name changed

Season

 

[3DDave]

Still has a semicolon in the filename.

 

[pmarc]

SeasonLee,

Each cell in the table for case D can be expressed mathematically as (T+B+S)/2, where:
T - the tolerance value specified in the feature control frame (which is 0.4 for all cells).
B - the available bonus tolerance (which is a difference between the 'considered feature size' and the LMC size (23.5) of the larger diameter).
S - the available datum feature shift (which is a difference between the 'datum feature size' and the LMB size (11.8) of the datum feature).

So the value in cell [24/12] comes from: (T+B+S)/2 = (0,4+0,5+0,2)/2 = 0,55
And the value on the diagonally opposite side of the table in cell [23,5/11,9] comes from: (T+B+S)/2 = (0,4+0+0,1)/2 = 0,25

One problem with these tables, in general, is that the terms 'considered feature sizes' and 'datum feature sizes' are not precise. They should rather be:
- 'considered feature UAME sizes' and 'datum feature UAME sizes' in cases A, B, C and E.
- 'considered feature UAMME sizes' and 'datum feature UAMME sizes' in case D.
But as you know, the terms did not yet exist in Y14.5M-1994.

 

[pmarc]

Also, Season Lee's example appears to have a non-URL character in it making it not down-loadable.

Still has a semicolon in the filename.

If you are able to download the file (I am) and knowing what the extension of the file is (.xslx), just manually add the extension to the file name and this will let you open it.