How to Read Orthographic Views: Front, Top, Side, and Projection Methods

Why Orthographic Views Exist: One View Can't Define Geometry

This is a trick that I try to use as much as possible. Drawing an element of a product from one single vantage point forces you to focus on only the most salient information. Because when you attempt to render a part from one angle, certain details either vanish, become confusing, or simply do not translate correctly to the drawing.

In order to avoid the problems of the perspective view, the orthographic view represents the object from several perpendicular directions, typically front, top, and side. Each view provides all of the necessary information that you would see straight on when viewing that particular section of the object.

But this matters more. With dimensions drawn in a true dimension space, the dimensions remain accurate. A part labeled 50mm long is really 50mm long. Perpendicular edges and planes will remain perpendicular on the drawings. Square angles will remain square. Because the projection methods used in creation of these drawings are based on orthographic projection, the measurements can be read directly from the drawings, and the machinist doesn't have to worry about inflated dimensions caused by perspective.

What a View Actually Shows: Two Dimensions, One Missing

In an orthographic view, the view of a solid object is a projection of the object onto a plane. This means that there is a direct relationship between a view of a part and the view of that part as it would appear when looked at from one direction. If you were to look at a part straight on and then draw what you saw on a piece of glass, that would be one view.

Standard engineering drawings typically use three views:

Front view: The front view is your primary orientation for describing a part geometry. It is typically the most well-known view of a part and is the first view selected before developing the other views.

Top view: A view taken directly from above. It shows the width and depth, but the height is not shown.

Side view: Commonly viewed from the right side in US drawing views (third-angle projection). The side view illustrates and specifies the height, depth, but not the width of a product.

Most people don't realize that each of these views are actually two dimensions that attempt to portray three. The front view for example shows height and width but does nothing to represent the depth. Similarly, the top view shows width and depth but again, does nothing to show height. In order to gain a complete understanding of an object in three dimensions, one needs to see several of these views at the same time.

View Alignment: How Features Map Between Front, Top, and Side

The orthographic views are not intended to be read in isolation, but rather as a system: you should be able to follow features from one view through to the others.

And it's generally speaking the same rule with alignment (though it can be easier to visualize, for some people, by considering the corresponding features vertically rather than horizontally). Features which are aligned horizontally will therefore correspond with the same edges or surfaces. So if you see a hole in your front view, try looking just above it (or below, depending on how you're projecting) in your top view; you should see that same hole staring back at you from a slightly different angle.

Features that are vertically aligned between the front view and the side views are corresponding features. An edge on the right side of the front view corresponds to an edge on the left side of the right-side view.

The dashed lines (hidden lines) indicate that the geometry is there but not visible from this view. There may be a hole on the back side or a pocket that is not visible from the front view.

By looking at multiple views of a component, it is possible to build up a 3D model of the part by matching edges, apertures and surfaces across the different views. This can be a learned task, and some people may find it easier than others. However, with practice it can become almost intuitive.

Projection Standards: First-Angle vs Third-Angle View Placement

Orthographic drawings can differ depending on the region.

This is not trivial. Misunderstanding the method of projection can lead to misunderstanding the geometry in the drawings. It is wise to check the projection symbol in the title block before trying to understand if a view is created from the left side or the right side. The projection symbol is usually a relatively small symbol that is placed in the top right corner of the sheet in the title block. It contains two truncated cones representing first angle and third angle projections.

Hidden Features Across Views: When a Hole Becomes Dashed Lines

Some features are only visible in certain views while others are visible in all views, but drawn as a solid (visible) or as a dashed (hidden) line.

This is a fundamental concept to understand for 3D modeling: a simple through hole looks like a circle from the front and top views, but like two dashed vertical lines from the side view. The reason for this is that from the side view, you are seeing the edge profile, or the contours that outline the 3D object from that vantage point. The hole is, of course, situated inside the object, but its presence is not detectable when viewing from that 90 degree angle.

Internal features such as counterbores, internal diameter's, pockets, blind holes and slots are dimensioned with dashed lines if the feature is inside the part or hidden on a surface that is not visible from the perspective of the current view. Many features require multiple views as they may be hidden in one view but clearly visible in another.

In many cases it is required to reference all three (or more) views of a planset in order to understand its complex internal geometry. Viewing only one plan or section typically is not sufficient.

When Orthographic Isn't Enough: Recognizing When a Section View Is Needed

Hidden lines can be very effective at clearly communicating part geometry, especially when the part includes multiple features and contours. However, there is a point at which so much internal geometry that is indicated by hidden lines can start to look overly complex and difficult to interpret through hidden lines. Section views are an alternate method for providing insight into the intricacies of such geometry, and involve drawing a view of a sliced or cut part, viewed from the cut surface.

Section views show internal features that would otherwise remain hidden, thus solid boundaries that would be dotted lines in other views are made solid. Crosshatching ( diagonal lines ) is used to indicate cutout areas within solids.

Section views are useful for simplifying a drawing for reading purposes, by removing superfluous centreline dashed lines and clearly showing internal features such as pockets and bores.

When a drawing includes a section view, it means that the internal features of the product would be too complicated to make sense with straight orthographic views with hidden lines.

Why This Matters: Spatial Errors Create Manufacturing Errors

The biggest mistakes when reading an engineering drawing are looking at views individually and not in tandem. Most drawings are composed of several views, and the biggest mistake that someone can do is become 100% confident of a part after studying the flat plan view (front view) only to find discrepancies in the birds eye view (top view) or side view that are quite revealing to the lack of overall understanding of the part.

Level 2 requires Spatial Thinking, the ability to assemble a 3D shape from 2D views. You can't skip this step. You must be able to mentally build objects from drawings, and understand how shapes appear from different angles.

• know where dimensions are applicable (horizontal or on an angle, or even both, is the 50mm measured across or along the box edge)
• Read geometric tolerances correctly (i.e. what surface is the datum?).
• See how different components interact and fit together within assemblies (is the part a tight sliding fit into a hole or a proximity fit next to another part).
• See pitfalls during manufacturing before they occur (e.g. whether or not the interior corner can be machined with standard tools).

If you get it wrong, everything that follows is more difficult, more time consuming and potentially error prone. Mistakes in dimensioning, tolerancing and assembling part drawings can result in parts being machined incorrectly, impossible tolerances assigned, assemblies that are impossible to assemble and parts that are impractical to manufacture. Learning to effectively use orthographic projection is therefore a critical skill that every designer and machinist should strive to obtain, either by learning it properly or through painful experience.

How Level 2 Builds on Level 1

In Level 1 you learned the visual language of lines, title blocks, standards, and scales. You learned what the typical symbols mean and where to find information on a typical drawing.

In Level 2, one puts the language to work recognizing 3D geometry by studying a part from multiple views. Multiple views of different parts are studied to recognize and identify the actual 3D shape of real parts.

Both of these training modules will provide you with the basic skills necessary to read and interpret any type of standard, complex, engineering drawing. You will learn how to determine the type of projection used to create a drawing, interpret and relate multiple views found in a single drawing, and mentally create a 3D image of an object from the 2D projections found in a typical engineering drawing. All of the rest of the advanced topics will then become easy to understand.

Task: Combine Three Views Into One 3D Interpretation

This tutorial uses a simple pen and pencil sketch of a classic wooden racing car made in 3 third angle projection views (Front, Plan and Section) for working from scrap paper drawings. The views are typical for a range of sketching projects and model-making designs.

• Side On view : Same shape as front view and includes a rectangular plane protruding from base of tail with rectangular slot which is positioned centrally and is pointed towards front.
• Top: Same rectangular shape. Same central circular feature, shown as a circle instead of an arc.
• View from right side of model. rectangular outline with 2 dashed lines to indicate hidden feature. 2 horizontal lines to indicate that it is concealed.

Questions to test your understanding:

1. The circular geometry is a boundary feature.
2. Why does the hole appear as dashed lines in the right side view?
3. Where would the right side view go if this was a first angle projection?
4. What can you learn by reading all 3 views that you wouldn't learn from reading any single view?

There is an often overlooked aspect of drawing orthographic views, and that is they need to be part of a coordinated system. As we speak about hidden lines, we need to recognize the hidden lines simply reveal the geometry that is not visible from a particular angle. As we speak about how to handle project lines, we need to understand that different methods for creating orthographic views will demand a different location for that view. The bottom line is you cannot gain a complete understanding of an object's features by piecing together information that you think you gather from individual views. Rather, you have to gain understanding from all of the views taken together.