Geometric Dimensioning and Tolerancing
Geometric Dimensioning and Tolerancing
(OP)
mm2c (Mechanical) 13 Mar 05 20:07
can anyone explain the proper use of
PROFILE when the part is dimensioned using +/-
tolerances instead of BASIC dimensions?
can anyone explain the proper use of
PROFILE when the part is dimensioned using +/-
tolerances instead of BASIC dimensions?





RE: Geometric Dimensioning and Tolerancing
RE: Geometric Dimensioning and Tolerancing
All the tolerances applied to the part must be satisified by the fabricator. Any features that satisifie the most accurate tolerance ought to satisfy the less accurate ones.
The only problem with this is that you might have a control that allows the feature only to exceed the nominal material condition, and another control that allows the features only to be inside the nominal material condition. This is a mistake, and you will have to fix it.
Consider the case that you have a part with an elaborate outline to which you have applied a profile tolerance of 0.5mm. You apply the all-around symbol. You apply basic dimensions all around with one exception. To that, you apply a tolerance of +/-0.1mm. You could just as easily have applied a tighter profile, but the +/- tolerance could be exactly what you need.
Any feature falling within the +/-0.1mm feature also falls within the 0.4mm profile. The part can be inspected. The drawing is valid.
There is a way to apply a profile tolerance to all the features except your accurate one, but it is slightly complicated. If you have more than one accurate feature, it is a lot more complicated.
The whole point of basic dimensions is that you are indicating that the feature is controlled by a geometric specification. You should use basic dimensions unless you need an additional control.
JHG
RE: Geometric Dimensioning and Tolerancing
RE: Geometric Dimensioning and Tolerancing
RE: Geometric Dimensioning and Tolerancing
All dimensions MUST be basic for the outside profile.
We just started a GD&T training class this morning and the instructor emphasised this point.
"Wildfires are dangerous, hard to control, and economically catastrophic."
"Fixed in the next release" should replace "Product First" as the PTC slogan.
Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand
RE: Geometric Dimensioning and Tolerancing
Best Regards,
Heckler
Do you trust your intuition or go with the flow?
RE: Geometric Dimensioning and Tolerancing
According to the standard, you can use +/- dimensions to locate the profile. The profile itself must be dimensioned with basic dimensions. Ask your instructor about paragraph 6.5.5 and figure 6-18 (as pointed out by PaulJackson).
RE: Geometric Dimensioning and Tolerancing
Most automotive parts now have very little conventional dimensions on them partially due to the fact that the shapes are so complex it would be impossible.
So parts are toleranced from a model. A profile is like a flat “C” at -90 degrees and should be followed by a size say 0,5, a surface is like a flat “D” at 90 degrees and again is followed by a tolerance.
This denotes the diameter of a circle or sphere that runs along the true model and the part must be within this.
So to this standard there are no +/ - dimensions as such, however you can have only – dimensions by making the tolerance unilateral, in which case the whole tolerance is on one side only.
RE: Geometric Dimensioning and Tolerancing
If you reread the original posting it says 'instead'. That means to me there aren't any basic dimensions.