Bonus tolerance?

[aldumoul]

Looking at the "Datum B feature," if Datum A increases from MMC, can you add this as bonus tolerance/gain tolerance?

 

[KENAT]

Do you have a drawing, or at lease some more context?

ARe you thinking of datum shift?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[aldumoul]

(forgot to click the "add link" hyperlink)

 

[powerhound]

In this case I believe you can add the amount that datum feature A has departed from MMC to the total positional tolerance, so in effect, yes, you do get extra tolerance--but not really--but there are 2 things to keep in mind:

1) It is not bonus tolerance, it is datum shift. Your tolerance zone is not getting bigger, it is moving. I know it looks like it's getting bigger but it's not.
2) It doesn't always work out this way so don't get it in your head that in every case, all you have to do is add the datum shift to the bonus tolerance.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
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[Belanger]

Second Phound's post! On one hand the shift tolerance gives you more "effective" tolerance (in this case!) but it's not really making the position zone bigger, but rather adding in the shift or play factor regarding datum A.

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

http://www.gdtseminars.com

 

[aldumoul]

Also, don't the positional tolerances supercede the parallel/perpendicular callouts?

 

[Belanger]

No, because they're referencing different datums.

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

http://www.gdtseminars.com