Les Hirst, P. Eng.
Design Guide, Berlin KraftWorks Inc.
In this post, we’ll explore why well executed engineering drawings are still essential – in this era of 3D printing, 3D CAD, and the outsourcing of manufacturing.
As a college teacher and design advisor to start-ups, I’ve noticed that young mechanical designers have a great aptitude in 3D modeling, but often don’t direct much effort to the creation of detailed engineering drawings. I can understand the motivation for this. 3D modeling is fun – kind of like the electronic equivalent of working with modeling clay – and creating drawings just seems like a lot of tedious work. Even though the creation of a simple drawing layout from a 3D model is incredibly easy with modern design software, the harder work comes in when we apply dimensions, tolerances, and detailed notes. This is the type of notation that requires us to identify important functional relationships and limit the allowable dimensional variation that will ensure that functional requirements are met.
Developing mastery in creating drawings takes time. Unfortunately, the shift in the typical environments for young designers often doesn’t support this development. When I began my career, most college and university engineering grads would begin work at medium or large size companies – where we took on junior design roles and learned how to create drawings from experienced designers who knew the products well. I call this the guild model of learning. Let’s contrast that with a common situation today - where recent grads are often the only mechanical designer in a start-up environment and are expected to create drawings for a wide variety of parts and assemblies. I can really empathize with them, as they’re in a situation where they have to either figure it out for themselves or contract out the work.
So the question arises – Do we even need detailed drawings anymore? After all, they seem like a relic of when drafting boards ruled and 3D printers didn’t exist. Isn’t the 3D model good enough?
Great points. To question 1: there is an alternative method called model based dimensioning (MBD), where all of the information normally contained on drawings is applied directly to the 3D model. I suspect that this will take over from drawings eventually, however it’s not yet widely used and the early implementations of it in software have been awkward to use. In this article, drawings and MBD are considered to be equivalent. To question 2: actually, we can get away with minimal or no drawings in the early proof-of-concept and subsequent industrial design phases. But once we get to the NPI phase, where we’re designing parts for testing, compliance certifications, and ultimately production, the information contained on drawings is essential for four key reasons:
1. Design – Documenting Requirements with Unambiguous Language
Designers need to capture the higher level design intent for the product (e.g. ease of assembly, alignment, gap consistency, reliable sealing, etc.) and ensure that the manufactured component parts meet this intent. In order to do this, the critical characteristics and dimensional variation of these parts must be documented and clearly communicated to whomever is manufacturing and inspecting them. Engineering drawings accomplish this function, using common standards and languages developed by organizations such as ISO and ASME. In addition to clear communication, the creation of engineering drawings forces the designer to carefully consider how the component parts support the overall design intent.
2. Supply Chain – Quoting
Drawings contain key information - such as tolerances, identification of critical dimensions, material specifications, finishes and coating – that do not typically exist on a 3D model. This information is critical for a supplier to quote accurately on a job. A supplier’s business success depends on meeting the specifications on the design documents at the lowest possible cost. If the specifications aren’t fully and clearly communicated, the resulting parts may not meet design intent.
3. Operations - Manufacturing and Inspection
The manufacturer will select machinery, processes, tools, and fixturing to ensure that parts are produced at the lowest cost that consistently meet the dimensional tolerances and other characteristics specified on the drawing. Parts can then be inspected to unambiguous requirements on drawings, represented with standardized symbolic language, allowing for in-process control and reporting. This applies regardless of whether the parts are produced in-house, locally, or at an overseas contract manufacturer.
4. Legal – Contracts, Compliance and Protection
The drawing represents what the manufacturer agrees to produce and is a contractual document, along with the purchase order and other documents. If the parts shipped don’t meet expectations, the first question should be: do they comply with the drawing specifications?
In the unlikely event that the end product causes damages, and either civil or criminal charges are brought forward, the drawings will likely be used as evidence to assess whether or not proper care was taken in the design. The question then may be: do the drawings and other documentation ensure that the design complies with safety and regulatory requirements?
We can see how clear and complete engineering drawings are essential for ensuring that product requirements are reflected in the design, that the manufactured parts meet those requirements, and that legal considerations are given due care. Doing the drawing work up front can save a lot of headaches down the road as well as expedite the time to market.