Simple Question - relates to if Bonus Tolerance is possible.

[brandnew1]

i believe this to be a silly question but i'm no expert and thus i just want to verify if this is the same or valid interpretation.

There is a true position callout with a M modifier to datum A. i've always interpreted this where the feature (square slot) needs to be 'centered' to Datum A no more than .001 out of position. If this was a diameter i would add "Bonus tolerance" if the diameter moved away from maximum material.

The Question: This being a square slot, does bonus apply here if the dimension is greater than .252?

The more difficult question: Is there a basic rule that indicates when looking at FCF's, its very "clear" that it is a datum shift allowance versus "bonus"? (what i mean by this, if i see the circle M on a datum in the FCF this is a shift, but if the M is inside the tolerance this is something else?

thank you

 

[chez311]

Is there a basic rule that indicates when looking at FCF's, its very "clear" that it is a datum shift allowance versus "bonus"? (what i mean by this, if i see the circle M on a datum in the FCF this is a shift, but if the M is inside the tolerance this is something else?

Yes.
(M) applied to a tolerance value is called MMC or Maximum Material Condition. The concept of bonus tolerance is applicable.
(M) applied to a datum feature reference is called MMB or Maximum Material Boundary. This does NOT provide bonus tolerance. This allows datum feature shift.

You may want to familiarize yourself with these concepts and on the differences between MMB/LMB datum feature shift and MMC/LMC bonus tolerance. A good thread I always like to reference is below. The figure from CH on his post (17 May 18 14:59) shows the difference very well.

https://www.eng-tips.com/viewthread.cfm?qid=439000

 

[brandnew1]

thank you chez311 for the quick answer and the reference to the other thread...i downloaded the attachment =)

 

[pmarc]

brandnew1,

I hope you will also read the comments that followed the CH's post in the referenced thread.

 

[brandnew1]

Hi pmarc,

i did read further below the thread but it probably take time for me to digest.