Anatomy of an Engineering Drawing

Engineering drawings, also known as technical drawings, provide detailed 2D images of a part and include essential manufacturing data. They ensure that the designer and machinist clearly understand the project's technical requirements.

A good engineering drawing specifies design intent so clearly and concretely that the inevitable variances you see with manufacturing processes don’t result in low-quality, inconsistent components.

Components of an Engineering Drawing 

In CNC machining, engineering drawings are essential companions to 3D models, and often, machinists can create a part using just the technical drawing.

The following are the key components of a technical drawing that engineers use to convey design intent and machinists use to manufacture precision components.

Title Block

The title block is in the bottom right corner of the document. It includes essential details like the part name, the names of the team members involved (design, checking, and approval), and the company name. It includes technical details like measurement systems, projection angles, surface finish needs, scale, and material. The title block template can be standard or custom.

Coordinates

Coordinates are typically found along the edges of large or complex technical drawings. They act as reference points for discussing the drawing's details.

Isometric View

An isometric view is a 3D image of a part. Including it in a technical drawing is often helpful, as it makes it easier for machinists to understand the part's shape. It also provides details like how to install the part and its build orientation.

Orthographic Views

Orthographic views provide key details about a part's shape. They include most of the dimensions and tolerances. These are 2D images of a 3D object, viewed from the front, top, and side. Hidden lines can be added to orthographic views to show important features that aren't visible. Usually, two or three orthographic views are sufficient to accurately represent a part's entire geometry.

Section View

A section view is a 2D image showing the inside of a part when it's cut open. It reveals internal features not visible in isometric or orthographic views and is typically aligned with an orthographic view. In orthographic views, a labeled cutting line indicates where the part is sliced to create the section view and shows the cut's direction. Section views have crosshatch patterns to highlight where material was removed. Complex parts might have multiple section views.

Detail Views

When an orthographic view has complex areas that are hard to measure, detailed views are used to focus on these parts. These detailed views can be any size and placed anywhere in the drawing. They are marked with a single letter indicating which part of the orthographic view is being detailed.

Notes to the Manufacturer

Manufacturer notes are typically found at the bottom left of the technical drawing or above the title block. They provide extra details not shown in the drawing and give instructions for the machinist. These notes might include directions to break and deburr sharp edges, specify surface finish requirements, or list other components to be assembled with the part.

Best Practices for Technical Drawings

There is no exhaustive list of best practices to implement into your technical drawings, but we’ll leave you with a few final tips and guidelines to keep in mind.

Call out features that are “inspectable”

Just as dimensions are based on function, inspections are based on dimensions. A drawing with clear dimensions between functional parts not only shows clear design intent but is also easier and cheaper to inspect. The closer the inspection measurements are to functional parts, the less likely a part will pass inspection but fail in function. Always aim for a direct link between inspectability and functionality.

Dimension what you can measure

Similarly, ensure you dimension the physical features of your part. Avoid using non-measurable datums. Whenever possible, dimension to a physical feature instead of a part centerline or CAD modeling plane. Centerlines and center planes require inference from other geometry during inspection, which can complicate in-process inspection steps. An exception to this is hole centers.

By dimensioning in this manner, you guide the manufacturer on which features and surfaces require special focus and which are less critical. Identifying what is less important can save significant manufacturing time by allowing for more lenient tolerances and quicker production in non-essential areas.

Leave very clear notes for the manufacturer

Be clear and specific in your drawings. A brief note explaining a feature's purpose helps machinists and fabricators make informed decisions during programming, setup, and manufacturing.

Convey design intent as clearly as possible

This is by no means exhaustive, but here are a few quick tips for making clear and legible drawings.

• Don’t cross dimension lines and don't dimension hidden lines
• Employ ordinate dimensions whenever possible
• Use as many section views, detail views, and pages as necessary to convey manufacturing intent without ambiguity, but no more than that (we know – a tough needle to thread!)
• Write clear and straightforward notes. These notes should resolve any confusion in the drawing or provide additional details to express design intent, such as drill bit size, form tap hole, or ream to fit.
• Use the space you have to add appropriately scaled projected views
• Include an un-dimensioned isometric view. This view helps communicate 3D at a glance and can be different than the drawing scale used in all other views.