Can I omit Basic dimensions?

[bc23]

My drawings are created (& read) in 3D format (MBD). I read an article that basic dimensions can be omitted in MBD; the main advantage being shorter dimensioning time. I only know 2 situations where basic dimensions are required:
(a) for designer's information (to track changes or apply in calculations etc),
(b) for CMM application

Does anyone know of other conditions which would utilize basic dimensions?
Does ASME have any rules regarding omission of basic dimensions?
Note that since I have provided the drawing in MBD, any unknown dimension can be checked from the 3D.
Hope to understand what I'm missing.

 

[greenimi]

Note that since I have provided the drawing in MBD

So, if it is MBD then why you need a drawing for? What exactly you are showing on your "drawing" ?

 

[greenimi]

And Y14.5-2018 states

5.1.1.2 Basic Dimensions. Basic dimensions shall beindicated on the orthographic views or in the model in one of the following ways:
(a) applying the basic dimension symbol to each basic dimension. See Figure 10-1, illustrations (a) and (b).

(b) specifying on the drawing (or in a document referenced on the drawing) a general note such as “UNTOLERANCED DIMENSIONS ARE BASIC.”
See Figure 10-1, illustration (c). NOTE: When using this method, a plus/minus tolerance is not allowed via a general tolerance block or notes.

(c) implied basic dimensions of 0° and 90°. See paras. 4.1(k) and 4.1(l).

(d) specifying and querying basic dimensions on models. See ASME Y14.41.

 

[ctopher]

I agree, look up ASME Y14.41.
MBD still uses basic dims.
You can create 3D PDF showing the MBD views and notes for vendors/customers.

 

[3DDave]

This is really a question for the recipient and user of the drawing/model.

Can they use what you are producing or not?

It is a little confusing to refer to a model as a drawing.

 

[ctopher]

3DDave It is a little confusing to refer to a model as a drawing.

Haha. I hear this all the time! It is confusing.

 

[ewh]

In MBD there is often a default profile tolerance applied to un-dimensioned features, simplifying the model by only dimensioning items that have a non-default tolerance. These datums/features do need to be defined with basic dimensions (or a note as mentioned above) and applicable FCFs. This applies in the absence of actual drawings or if the drawing only consists of non-orthogonal model views. YMMV

 

[bc23]

So, if it is MBD then why you need a drawing for? What exactly you are showing on your "drawing" ?

Hi, the MBD shows non-general tolerances for specified profiles. E.g. Diameters, linear dimensions, but mostly GD&T spec's.
Thanks, I think 5.1.1.2 (b) will be useful for me.

 

[bc23]

Thanks everyone for the input, you've helped to give a clearer picture.
Sorry for the confusing terms, as we are transitioning from 2D to MBD, we still use "drawing" & "MBD" interchangeably. (actually we say 3DA instead of MBD).

3DDave: You are right about recipient of MBD, unfortunately they are also unclear, so actually we are "trialling" some drawings without Basic dimensions.

Meanwhile I also found some clarification on J.P. Belanger's site (for anyone else interested). Not sure if I can share the link, so I've omitted it.

 

[3DDave]

The model itself, if a model is sent, has only basic dimensions for mutual locations of surface geometry; they literally cannot be omitted. The model record of the surfaces will include no tolerances. If the model is parametric, the parameters that drive the model can include tolerances, but that isn't part of ASME Y14.41 exchanges as far as I recall.

What might be omitted is model dimension features; that is, records in the model of specific graphics that announce dimensions and have "dimension" recorded as the graphics type and would for display in software that cannot make measurements. These act as text or other non-surface/non-solid graphics located in the 3D space of the model.

You might answer these questions by contacting the recipient and sending a trial part.

 

[ctopher]

I have done testing this past year with MBD. I have sent 3D PDF's with STEP 242 files. I found out majority of our vendors don't want it. They are used to 2D dwgs, they still want PDF's of the 2D dwgs along with STEP files.
If I try to force the issue, and train them how to use it, they say the price will go up. Weird.

 

[drawoh]

My drawings are created (& read) in 3D format (MBD). I read an article that basic dimensions can be omitted in MBD; the main advantage being shorter dimensioning time. I only know 2 situations where basic dimensions are required:
(a) for designer's information (to track changes or apply in calculations etc),
(b) for CMM application

Does anyone know of other conditions which would utilize basic dimensions?
Does ASME have any rules regarding omission of basic dimensions?
Note that since I have provided the drawing in MBD, any unknown dimension can be checked from the 3D.
Hope to understand what I'm missing.

You may leave out the basic dimensions if the fabricator has your 3D model. Is this a good idea?

How will your vendor and you inspect your part?

 

[3DDave]

Since geometric characteristic tolerances are controls of the deviations from the nominal geometry and the model should be built to the nominal geometry, there should be no problem. The alternative is to create false "basic dimensions" that do not represent the nominal geometry and that would be bad.

 

[greenimi]

Since geometric characteristic tolerances are controls of the deviations from the nominal geometry and the model should be built to the nominal geometry, there should be no problem. The alternative is to create false "basic dimensions" that do not represent the nominal geometry and that would be bad.

3DDave,
Since you seem to be very knowledgeable on this subject (and I am always learning something from you even sometimes you have nasty disputes with Burunduk here is the link for the Y14.41 draft which is in the public review until 05/07/2025.
You can read it and provide pertinent feedback for the committee members, if you want.
Don’t ask me, if they will implement or not that you are going to comment or any change proposals you gonna make, but at least I can tell you, from my experience, that they will read it. Well, if that’s enough or not for you to make comments, ONLY you can decide.

https://cstools.asme.org/csconnect/PublicReviewPage.cfm?SearchType=PublicReview&SortBy=DesignationTitle&StartRow=11

 

[3DDave]

https://cstools.asme.org/csconnect/Filedownload.cfm?thisfile=PublicReviewDraft3230.pdf&dir=ANSI.BSR8&45726.5038773

to save digging through all the other standards.

Perhaps carry this back

an·no·ta·tion
/ˌanəˈtāSHən/
noun
a note of explanation or comment added to a text or diagram.

Their definition:



Why does the Y14.xx group overwrite the commonly used definitions for words? They could have used "mark-up" which is a synonym for "annotation." It's like saying Tolkien "annotated" 1000 pages to his title work.

If there was text that said "This coating is because the alkali environment would degrade the aluminum surface and we could not count on anodize to do so." That would be annotation. A note "COAT PER .... " is a requirement that is a basic part of the description of the part and isn't annotation.

 

[bc23]

The model itself, if a model is sent, has only basic dimensions for mutual locations of surface geometry; they literally cannot be omitted. The model record of the surfaces will include no tolerances. If the model is parametric, the parameters that drive the model can include tolerances, but that isn't part of ASME Y14.41 exchanges as far as I recall.

What might be omitted is model dimension features; that is, records in the model of specific graphics that announce dimensions and have "dimension" recorded as the graphics type and would for display in software that cannot make measurements. These act as text or other non-surface/non-solid graphics located in the 3D space of the model.

You might answer these questions by contacting the recipient and sending a trial part.

It is a parametric model, and I have mostly GD&T spec's to define/control critical profiles. For these GD&T spec's e.g. True Position, there will be accompanying basic dimensions, which I will show (because True Position requires the basic dimensions for CMM measurement). However for others like Profile of surface, I would omit the basic dimensions (unless required by designer, or requested by other process engineers).

 

[bc23]

I have done testing this past year with MBD. I have sent 3D PDF's with STEP 242 files. I found out majority of our vendors don't want it. They are used to 2D dwgs, they still want PDF's of the 2D dwgs along with STEP files.
If I try to force the issue, and train them how to use it, they say the price will go up. Weird.

Haha, this is my experience as well, using JT-PDF as our format. But we are trying to push it through regardless. I think our push is mainly based on positive MBD reports from (US) aerospace & automotive industries. Just how much "value" MBD can create vs "cost up" is probably the big question.

 

[bc23]

You may leave out the basic dimensions if the fabricator has your 3D model. Is this a good idea?

How will your vendor and you inspect your part?

As I mentioned, I will have geometric controls for key features. The main idea was to omit what I thought was unused basic dimensions.

 

[greenimi]

I have done testing this past year with MBD. I have sent 3D PDF's with STEP 242 files. I found out majority of our vendors don't want it. They are used to 2D dwgs, they still want PDF's of the 2D dwgs along with STEP files.
If I try to force the issue, and train them how to use it, they say the price will go up. Weird.

Concur. At least, in my neck of the woods, I get the same experience. Unfortunately (and sadly). Having a 3D CAD annotated model is useless for most of our vendors and suppliers. Again, OURS.

They CANNOT use the PMI in manufacturing. Some can use the PMI in inspection, but only with significant upgrades (example Calyposo Direct CAD Importer is an expensive addon) which upgrades they don’t want to do it and exactly as you said –"If I try to force the issue……… they say the price will go up. Weird”

However, I don’t really find it weird. I find it …how can I say….Normal. This is the reality. If you (customer) ask me to upgrade my systems to be able to read YOUR 3D CAD models then it is not abnormal for me to recoup my investment directly from you (since you are the main culprit).

It is sad that’s happening that way? Yes it is. But this is how the system works. For better or for worse.

 

[ctopher]

Concur. At least, in my neck of the woods, I get the same experience. Unfortunately (and sadly). Having a 3D CAD annotated model is useless for most of our vendors and suppliers. Again, OURS.

They CANNOT use the PMI in manufacturing. Some can use the PMI in inspection, but only with significant upgrades (example Calyposo Direct CAD Importer is an expensive addon) which upgrades they don’t want to do it and exactly as you said –"If I try to force the issue……… they say the price will go up. Weird”

However, I don’t really find it weird. I find it …how can I say….Normal. This is the reality. If you (customer) ask me to upgrade my systems to be able to read YOUR 3D CAD models then it is not abnormal for me to recoup my investment directly from you (since you are the main culprit).

It is sad that’s happening that way? Yes it is. But this is how the system works. For better or for worse.

It's difficult these days to convince most people to grasp new technologies. Unless it's "toy like" 3D printing and robotics.