How Does an Engineering Drawing Differ from CAD?

By Protolabs

Manufacturing processes have come on leaps and bounds over the last century, as has how we navigate from thought to design concept and final product. In this blog, we will look at the key principles of an engineering drawing and how a CAD drawing differs from that. Whether you’re a seasoned engineer, engineering student or product design enthusiast, there will be some fascinating takeaways for you to digest.

engineering sketch


What are engineering drawings?

An engineering drawing is a detailed visual representation of a part (or anything else designed, such as a structure or object). These drawings convey precise information about dimensions, materials, tolerances, and all other specifications necessary to produce the part depicted. Engineering drawings often include various views, such as top, side and isometric. They also include annotations, symbols, and notes to help support easy fabrication and assembly.

CAD drawing for fixture model


What is a CAD drawing?

CAD (Computer-Aided Design) is a digital drawing or design created using specialised CAD software. These drawings are generated on a computer and are used across various industries to design parts, objects, buildings and more.
You can produce an accurate 2D or 3D model of your part using CAD software, incorporating all the specifications you’d expect in an engineering drawing, such as dimensions, annotations, materials, tolerances, and other specifications used to produce the final product accurately.
CAD software provides various features such as geometric modelling, parametric design, simulation, rendering, and analysis, enhancing the efficiency and accuracy of the design process.


How is CAD more precise than an engineering drawing?

Using CAD over an engineering drawing has many advantages, primarily around accuracy and efficiency; here are just a few advantages of using CAD software to design your part.

  1. Accuracy and Precision – CAD software allows for extremely precise measurements, often down to fractions of a millimetre or even smaller. This precision is due to the ability to zoom in and use exact numerical inputs for dimensions, ensuring consistency throughout the design.
  2. Elimination of Human Error – CAD minimises human errors, which can occur more frequently in manual drawings. Using automated tools reduces the likelihood of mistakes due to freehand drawing or misinterpretation of measurements.
  3. Dynamic Editing – CAD drawings are dynamic and editable. Changes to dimensions, shapes, or annotations can be made quickly and accurately. Any modifications made are automatically reflected throughout the drawing.
  4. Simulations and Analysis - CAD software often includes simulation and analysis tools. Engineers can test the functionality, structural integrity, and performance of their designs virtually. This helps in early identification of potential issues.
  5. Ease of Reproduction and Sharing – CAD drawings can be replicated, shared, and digitally transmitted without losing quality, allowing for seamless collaboration among multiple stakeholders.
  6. Standardisation and Compliance – CAD software often includes libraries of standardised components, symbols, and templates that comply with industry standards, ensuring that designs meet specific regulations or requirements.


CAD software on computer

Is it easy to make adjustments to a CAD drawing?

As explained above, making adjustments to a CAD drawing is pretty simple. CAD software offers a range of tools specifically designed for editing and modifying drawings. These tools include parametric design (parametric modelling allows changes to be made by altering parameters. When a parameter is modified, the entire drawing adjusts automatically, maintaining design integrity), editing tools (for shape manipulation, to move, stretch, rotate, mirror, delete elements), layers and components (allowing for different parts of the drawing to be organised and modified separately, similar to how you would a design piece in photoshop), history and undo function (like most software CAD allows you to undo or go back many steps in your design history), copy and mirror functions (for easy enablement of duplication). And collaboration tools (to facilitate real-time adjustments among team members simultaneously).


Are engineering drawings still used today?

Absolutely, engineering drawings are still very much in use today. While most manufacturers will require a CAD file to produce your part, engineering drawings are still used for initial concepts, legal documentation, legacy items, manufacturing references, etc.


How do you create an engineering drawing?

First and foremost, understanding the purpose of the drawing and what needs to be communicated is key. What is the level of detail required? Who is the intended audience? (manufacturers, contractors, engineers, etc.) Once that is determined, the next step is gathering all the necessary information, including dimensions and materials.
Once you have the purpose, audience and specifications, you need to decide how you will create your drawing. Will it be hand drawn? Or will you use CAD?
If you go down the manual route and draw your product you will need to start with the orthographic views (top, front, side etc.) using drafting tools like T-squares, rulers and protractors. For a CAD, simply open a new file and set up the appropriate units, scale and drawing settings.
The next step is adding all the dimensions and annotations. Include dimensions, tolerances, labels, notes, and symbols - ensure that all are labelled accurately. Once this is done, it's time to review and verify; always check for accuracy.
Then the file should be completed indicating revisions or versions if required. For manual drawings, consider proper title blocks and border information. For CAD, save the file in the appropriate format and include necessary metadata. Once all this is done the file can go for approval and your ready to go. Maintaining and revising the document as it goes through its lifecycle.



Is a CAD drawing for CNC the same as a CAD drawing for 3D Print?

Whilst both CNC and 3D printing utilise CAD drawings, there are differences in how the drawings might be prepared or optimised, due to the distinct nature of the manufacturing methods.

When designing for CNC, the part must be designed with a subtractive process in mind. The cutting away of material from a block would need to be incorporated into the CAD file. CAD drawings for CNC machining need to include specific instructions for toolpaths, tool selection, cutting depths, and tolerances. Apart from the standard dimensions, tolerances, and geometries required there is also a need for the clear annotation of different features, surface finishes, and any special instructions relevant for the machine operator.

When drawing for 3D printing, the part needs to be designed with an additive process in mind. Rather than removing material, it is built up layer by layer. CAD models must be solid and accurately define surfaces and internal structures. Specific considerations for 3D printing might include optimising geometries for printing, this would be considerations such as, adding support structures or adjusting orientations to minimise overhangs and improve printability. For 3D printing, details like, wall thickness, infill density, and surface smoothness, may be be more critical than when compared to CNC machining.

Whilst the fundamental principles remain the same, optimisation and specific requirements for CNC machining versus 3D printing can be significantly different. Understanding the nuances of each manufacturing process helps in the creation of CAD drawings tailored to the particular needs and constraints of the technology being used.