Question meaning of dimension and how to measure

[mmolt]

The attached image represents a generic question relative to dimensioning and measuring a part. Given a "U" shaped part, where the width between the two vertical legs of the "U" is dimensioned, and each leg of the "U" has an angular tolerance where is it appropriate to measure the dimension between the vertical legs?

The attached picture does a much better job of describing my question.

-Mike

 

[KENAT]

They should meet the width tol at both A & B.

The 90 degree is also keeping it from becoming a parallelogram.

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[mmolt]

Thanks for the response!

What if both angles measure 91 degrees? Obviously the dimension at B would be larger in this senario. Don't I get all (3) of the tolerances to work with?

-Mike

 

[KENAT]

"Don't I get all (3) of the tolerances to work with?" - in short no to my understanding.

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[KENAT]

Just realized, I should have asked what drawing standards you are invoking, as this might make a difference.

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[mmolt]

Thanks again KENAT...ANSI Y14.5.

 

[KENAT]

OK, so the linear dimension is controlling the distance between the 2 sides and because of 'rule 1' it is also controlling parallelism of those 2 sides to each other to within the tolerance.

The angular dimensions are controlling the perpendicularity to the base. It almost looks like you don't need both angular tolerances but at extremes of the linear tolerance both could come into play.

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[pmarc]

Linear dimension prevents both faces to be inclined to each other in opposite direction at greater than a certain angle. This certain angle depends on the linear dimension tolerance.

 

[powerhound]

This may be a good case for a restraint note.

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[MechNorth]

All 3 conditions must be met for part acceptance. Picture the FOS being at max'm (2.03), then you can't have +1 degree on either of the legs, but you may be able to have -1 deg (don't have the leg lengths so haven't done the math to see). Not an uncommon situation. May have been better defined with a datum and some perpendicularity controls.

Jim Sykes, P.Eng, GDTP-S
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[Belanger]

If the size is at its maximum, you can't have both legs be at +1º but I would say that you can have one of the legs be +1º and also have the other leg at -1º. This is because there is no Rule #1 type of relationship between size and orientation.

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

 

[MechNorth]

JP, wouldn't the length come into play.

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[MechNorth]

Never mind. My bad.

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