Minimum and Maximum PMI Dimensions

[EDCSRPM]

The use of Min and Max dimensions are often necessary as overriding modifiers to the dimensional tolerance scheme of a part. I appreciate that PMI is more reliable because of the inability to manually override dimensions from what the solid actually is. The reality is that min and max dimensions are necessary and that the model nominal is typically not the correct value to present as the min or max condition.

How can we use PMI in these cases?

Thin wall castings are a common use case. While min and max are often the lazy mans out instead of a proper tolerance scheme and stack-up, that is not always the case. It would be great if there was an option for defining a shift from nominal. Almost like an offset in CAM. That way it would be associative to the solid faces and consumable by NX CMM.

To date we've tried sketches and regular drafting dimensions in model space. Neither are associative and therefore defeat the value proposition of PMI.

All suggestions appreciated.

 

[JohnRBaker]

Have you tried using the tolerance option of 'Limits', as shown below:

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[EDCSRPM]

John,
Yes no issues using limits. What I need is a dimension with nominal and the appended abbreviation MAX, or MIN.

In your example the nominal is 5.000 what I need is an associative dimension of 4.995 MIN for example.

 

[JohnRBaker]

I think your only solution will be a custom program to create these PMI dimensions in the format that you're looking for. Now I'm not sure that that's even possible, but unless you can demonstrate that this dimension format is supported by one of the generally accepted Drafting international standards, there's little chance that we will ever enhance the PMI/Drafting package of NX so as to do this.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[EDCSRPM]

Thanks John, I appreciate your replies.

There has always been, and always will be a need to use Min and Max dimensions in unique situations where the summation of surrounding dimensional, form and position limits do not satisfy an engineering requirement. We strongly believe that this is well established within ASME Y14.5, and since ASME 14.41 refers to the former for dimensions on models (PMI/MBD), there should be no implied difference from the expectations set for a drawing.

How do you suggest that we approach getting the NX Drafting/PMI product owner to address Min and Max dimensions when the nominal condition does not reflect the engineering limit? This issue was raised last year at PLM world in a few round-tables relevant to these products.

Below are relevant ASME verbage supporting Min and Max conditions.

Excerpt from ASME Y14.5 2009 follows:
1.4 FUNDAMENTAL RULES
Dimensioning and tolerancing shall clearly define engineering intent and shall conform to the following.
(a) Each dimension shall have a tolerance, except for those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size).

2.5 SINGLE LIMITS
MIN or MAX is placed after a dimension where other elements of the design definitely determine the other unspecified limit. Features, such as depths of holes, lengths of threads, corner radii, chamfers, etc., may be limited in this way. Single limits are used where the intent will be clear, and the unspecified limit can be zero or approach infinity and will not result in a condition detrimental to the design.

 

[JohnRBaker]

The best way is to contact GTAC and have them open an IR pointing out that the NX Drafting/PMI capabilities are not in compliance with your referenced standards (provide as much detail as possible including the standard name and number as well as any specific sections/references). Most likely this IR will be converted to an ER which will be reviewed by the Product Management team responsible for Drafting/PMI.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[EDCSRPM]

Thanks again John!

 

[EDCSRPM]

John, Opened GTAC IR 7281061

If you can help get the proper Siemens people understanding and looking at this issue it would be greatly appreciated.
We have been working on implementation and are working through a long list of GTAC issues related to PMI and CMM. The end goal is not simply to replicate a drawing in a model, but rather to rethink what a definition must be to capture design intent and to be consumable for inspection.

Appreciate your time!

 

[Pockets4614]

ASME Y 14.41-2012 only references ASME Y14.5-2009 as a means to interpret dimensions. ASME Y14.41 Section 9 covers model values and dimensions. 9.2.1 states:
9.2.1 Basic Dimensions
Queried model values shall be interpreted as basic
dimensions unless superseded by a toleranced dimension
or defined as a reference dimension. Values queried
from the model for any feature(s) without a direct tolerance
relationship, or datum target specification(s)
assigned, shall be reference dimensions.

9.2.2 covers limit dimensions. MIN / MAX dimensions are not supported by ASME Y14.41. This makes sense as the intent of PMI is to give a machine the information needed to program. If you specified a MIN or MAX dimension it would require a machine programmer to select and apply the limit values needed to make the part.