Author: Duane Hess
As someone who is a trained and degreed draftsperson, it’s ironic that I advocate against drawings.
Drawings are representations of 3D objects
The very first thing to keep in mind is that a drawing is a 2D representation of a 3D object. It takes training and a certain cognitive ability to translate 3D to 2D and back again. Not everyone has that ability naturally. And this is only the graphical representation – the visualization of the object, not the engineering information that goes along with it.
Drawings are complex
The engineering information included with the visual representation is often more ambiguous than people, even engineers, realize. Every part feature must be defined with a dimension. For complex parts, that can mean tens, hundreds, or even thousands of dimensions. Clarifying what part feature dimensions apply to means creating additional drawing views of that feature, often using different perspectives and viewing angles. Those views are then tied back to the main orthographic projections that are the starting point for every part.
Drawings are static
A drawing by its very nature is intended to be a human-readable physical item, whether it is printed as an output from a modern CAD system or as a work of art that has been hand-drawn by a classically trained drafter. Drawings are a static document and the space available for views is governed by the physical area of the paper used. When all the room has been allocated, then a new sheet is added to accommodate additional views. For the consumer of the information, navigating from sheet to sheet to understand the relation of the feature to the overall part can be time-consuming, confusing, and error-prone.
For the consumer of the information, navigating from sheet to sheet to understand the relation of the feature to the overall part can be time-consuming, confusing, and error-prone.
Drawings are dense
2D drawing dimensions use leader lines and extension lines to denote the feature that they apply to. Complex part features may require many dimensions to define, and the density of the leader lines and extension lines make interpretation of the information difficult or ambiguous. To reduce drawing clutter and repetition, some of that dimensional information is relegated to notes or even the titleblock, as in the case of default tolerances. Notes may also contain references to other specifications or company processes. It is incumbent upon the drawing consumer to make the connections between the notes and the features they reference and to ensure that any processes or procedures referred to are accurate and up-to-date.
Drawings require time-consuming interpretation
The processes and procedures often further complicate the interpretation of the drawing because they include information that is not strictly tied to the engineering definition of the part and its function. Manufacturing and inspection processes become a part of the drawing documentation set and to fully interpret that information demands that the consumer understands those processes as well. Manufacturing capabilities are implicitly encoded in the part definition through tolerancing schemes, or explicitly with notes and procedural references. Inspection criteria may be set in a similar fashion. In both cases, the information captured on the drawing is often in addition to the engineering requirements, which creates additional interpretation complexity.
Drawings are inherently ambiguous
The final and ultimate reason drawings should no longer be used is their inherent ambiguity. Because of the physicality of drawings, the ability to connect the complex defining information to the feature that it describes is left up to the consumer and their ability to interpret it. The context of the information is often contained within the consumer’s experience in drawing interpretation and product knowledge. That context is lost over time as products age and people move on, leading to questions that can’t be answered.
Context is lost over time as products age and people move on, leading to questions that can’t be answered.
Models offer improvement opportunities
I have been in countless hours of client meetings as we execute MBE pilots on an existing product. The first step is to convert drawing information for an existing design to unambiguous, digitally connected, 3D, semantically consumable data. Those are a lot of adjectives, and each adjective provides an opportunity for manufacturers to improve and gain benefit from Model-Based Definition by transitioning away from drawings.
Models communicate more effectively
Personally, I based many years of my career on drawings and being the best drafter, the best communicator that I could be. I will always have a nostalgic fondness for the smell of paper, lead, erasers, and the ammonia of blueprints. But the reality is that there is a new way that is better. The modern manufacturing environment for everything from doorknobs to jet engines demands responsiveness, accuracy, and collaboration that is way beyond anything that I was ever capable of achieving with a drawing as a communication medium. My drafting skills have been obsoleted by Industry 4.0 and I’m okay with that.
Critically review your drawings
I challenge any modern manufacturer to test the fidelity of their drawings by converting them to a true digitally-connected Model-Based data set. I will help you. And I will be more than happy to bring my drafting kit along and create an artisanal drawing representation of your product if you cannot find some benefit of going fully Model-Based.