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.

 

[3DDave]

MBD isn't new. It's 30 years old and fails to be a substantial improvement at a large extra cost. It's a follow on to the "lights out factory" the DoD wanted to build where vast piles of raw materials, robots, and CNC equipment would be issued orders for on-demand parts which would be automatically produced without any people being involved. That's what STEP was intended to solve.

No doubt there are organizations that are sufficiently vertically integrated that they can use it, but I think they would have difficulty proving that it offers a significant cost savings except by focusing on the cost of plotters and paper.

The original basis for assuming it was cheaper was the supposition that using MBD would eliminate the need to create drawings, but the cost of drawings is mainly the cost of decisions about datum references, geometric characteristic tolerances, base topology, material, finish, and the analysis of the suitability for the function, plus all the decisions about the function. Making projected images onto 2D and displaying the requirements is a minor part of that.

One claim for savings is from those companies that fired their drafting group. In those companies the engineers would make rough models and somehow record many of the requirements and toss the models over the wall for drafters to make all the final dimensioning and tolerancing decisions as they made drawings. With no drawings, there's no need for the drafters and their salaries. Instead that effort is pushed back upstream to the engineers, who didn't make drawings and tend to do a bad job of it. The other cost saving is eliminating checkers, so when the task is back to engineering there's no one to be manage consistency. The software sales teams offer MBD as a solution.

"It is a parametric model" is not what comes out of STEP. The MBD workflow doesn't preserve the parametric model , unless you are on a completely integrated system down to QA/QC and the shop floor.

 

[SDETERS]

Why would a CMM program need Basic Dimensions? Are you using the 3D model to create your CMM program? How do you deal with the Basic dimensions that are rounded? For example, the model is 4.5654646 and the basic dimension says 4.565?

I am being curious at this point, and maybe a bit off topic.

Thanks.

 

[3DDave]

"For example, the model is 4.5654646 and the basic dimension says 4.565?"

That's a paddlin'.