Engineering Drawing Basics and Tips for Beginners

Purpose of Engineering Drawing

Generally speaking, it is tough and complicated to explain some specific engineering requirements in words. In this case, an engineering drawing with good size and proper scale can make it easier for the technician to understand and achieve the design intent. 

A single part’s engineering drawing gives a visual depiction of the part’s structure, dimensions, tolerances, and other requirements. A single-part drawing is frequently used as the unit of processing in the manufacturing industry.

Besides, an engineer can use an assembly drawing to represent a machine or equipment assembled from multiple parts to reach a particular function. Assembly drawings are frequently used to confirm that the actual fabrication of individual parts fulfills assembly requirements.

Applications of Engineering Drawing

Engineering drawing is essential for technical people. Compared to verbal or written descriptions, this method is brief and clearer. Engineering drawing is a critical part of almost all engineering projects. We can find that engineering drawing serves many critical applications:

1. It is used in ships for navigation.

2. For manufacturing of machines, automobiles, etc.

3. For the construction of buildings, roads, bridges, dams, electrical and telecommunication structures, etc.

4. For manufacturing electric appliances like TV, phone, computers, etc.

Types of Engineering Drawing

Engineering drawing can be grouped into 4 major categories: geometrical drawing, mechanical engineering drawing, civil engineering drawing, and electrical & electronics engineering drawing.

Geometric Drawing

Geometric drawing is the art of representing geometric objects on paper, such as rectangles, squares, cubes, cones, cylinders, spheres, and so on. Geometric drawing can be divided into plane geometrical drawing and solid geometrical drawing. Suppose the object has only 2 dimensions, i.e., length and breadth (as rectangles, squares, triangles, and so on). In that case, it is called plane geometrical drawing. It is called a solid geometrical drawing if the object has 3 dimensions, i.e., length, breadth, and thickness/depth (as cubes, prism, spheres, cylinders, and so on).

Mechanical Engineering Drawing

Mechanical engineering drawing is the art of representing mechanical engineering objects on paper, such as machines, machine parts, and so on. Mechanical engineers use it to express mechanical engineering works and projects for actual execution.

Civil Engineering Drawing

Civil engineering drawing is the art of representing civil engineering objects on paper, such as buildings, roads, bridges, dams, etc. Civil engineers use it to express civil engineering works and projects for actual execution.

Electrical & Electronics Engineering Drawing

Electrical & electronics engineering drawing is the art of representing electrical engineering objects or electronic circuits on paper, such as motors, generators, transformers, wiring diagrams, TV, phones, computers, etc. Electrical/electronic engineers use it to express electrical/electronic engineering works and projects for actual execution.

Methods of Making Engineering Drawing

Manual drawing and computer drawing are the two common methods of making engineering drawings. 

Manual drawing has been the primary engineering drawing method for the past few decades. People would use various tools to draw by hand, such as drawing boards, paper, rulers, calipers, round gauges, etc. But the manual drawing process is very tedious and unsuitable for contemporary manufacturing in pursuit of efficiency.

Computer drawing is more popular with contemporary manufacturers. It eliminates the tedious process of manual drawing and allows different versions of the design to be retained. Computer drawing is commonly used in CAD (computer-aided design) software. You can use CAD to create drawings from scratch. However, we recommend developing a 3D model and then making the drawings from it. The programs generate the views with just a few clicks. You need to add the dimensions, which saves time and effort.

Basic Components of an Engineering Drawing

A single drawing includes several elements with quite a few variations to each of them. Let’s take a closer look at the basic components of an engineering drawing so you can learn how to read engineering drawings.

Types of Lines in Engineering Drawing

Take note that all of the lines on an engineering drawing are equal. Various options are available for showing both hidden and visible edges of parts.

Continuous Line

The most common line type is a continuous line, often called a drawing line. It represents an object’s physical boundaries. Simply put, a continuous line serves to draw the objects. The line thickness varies. The inner lines are thinner, while the outer contour uses thicker lines.

Centre Line

The center line can show the parts with holes and symmetrical features. Symmetry can reduce the number of dimensions in a drawing while also making it more visually appealing and easier to understand for the reader.

Hidden Line

The hidden line is another type of line used in mechanical drawing. It can show something that would not be otherwise visible on the drawing. For example, the hidden line can show the length of an interior step on a part without using a section or cutout view.

Dimension & Extension Line

The extension line describes the object being measured. The dimension line contains two arrowheads between the extension lines and the measurement above (or inside) the line.

Broken View Line

Using a broken view line means that a view has been broken. If you have a 3000mm long and 10mm wide part with symmetric qualities, using a break-out offers you all the information without taking up as much space.

Cutting Plane Line

The cutting plane line displays the cutout’s trajectory using a cutout view. Thanks to the A-A cutting line, you can see that both types of holes are visible here.

Types of Views

An engineering drawing contains numerous types of views. These views all perform distinct functions. Adding views should follow the same logic as dimensioning. Note that you should only add a view that contributes to the overall comprehension of the design.

Orthographic View

The orthographic view is the core of an engineering drawing. An orthographic view or orthographic projection is an approach to depicting a 3D object in 2D. As a result, a 2D view must convey all information required for part manufacture. This approach of representation allows for the avoidance of length distortion.

We can use 3 different views in a multiview drawing to convey all the information, such as the front view, top view, and side view. It is conceivable that several extra views will be required to display all of the information. However, less is more.

Isometric View

Isometric drawings depict three-dimensional parts. All vertical lines remain vertical, while parallel lines are presented at a 30-degree angle.

The lengths of the vertical and parallel lines are true. Therefore, using a ruler and the drawing’s scaling, you may easily measure the length from a paper drawing. The same is not true for angled lines. With this type of view, engineers adhere to the dimensions instead of optical illusions.

Section View

A section view can readily reveal some of the part’s characteristics that are not apparent at first glance. The cross-section is preferable over hidden lines because it provides greater clarity. The cross-hatching feature is a cross-sectional view indicator.

Detail View

The detail view provides a close-up of specific sections in a larger view. Detail view is ideal when a huge part contains many vital dimensions in a small area. It is a good view of the readability of measurements.

Cutout View

The cutout view has the same image used to show the section view. With one exception: the side view contains cutouts. Cutouts can help decrease the number of distinct views on a single drawing. As a result, we could easily delete the section view and add all required dimensions to the cutouts.

Auxiliary View

The auxiliary view is an orthographic view to represent non-horizontal or non-vertical planes. It displays inclined surfaces without distortions.

Dimensions

In some instances, CAD models may lack vital information, such as GD&T and geometric dimensioning tolerances. The correct dimensions can guarantee the part a longer life with less maintenance. While you may automatically fetch all dimensions via the measure button, adding engineering tolerances requires manual intervention.

Information Blocks

Additional information is displayed in the little boxes in the bottom right corner. The title block lists the author’s name, quantity, coating, part name, part number, scale, etc. These information blocks may also contain material prices. It can be used better to understand all the parts of the technical drawing.

Assembly Drawings

The following points will help you better design assembly drawings and make your project in the machine shop more efficient.

• Keep in mind that these technical drawings aim to facilitate the assembly process.
• It should be clear where each part goes and how it is attached.
• Use tools like general dimensions, cuts, section views, numbered pieces, and detail views (or close-ups).
• Make sure the bill of materials has accurate information regarding part numbers, names, and quantities. 

Common Mistakes In Engineering Drawing

There are 4 common mistakes in engineering drawing:

1. Dimensions marking is messy, incomplete, omitted, and repeated.

(1) Avoid closed dimensions.

(2) You must directly mark the critical dimensions of the parts.

(3) Mark the size to make processing and measuring easier.

2. The placement of views is inaccurate, or they do not correspond with one another, and the design intent is unclear.

3. If the workpiece with high dimensional accuracy requirements is not marked with dimensional tolerances, it will cause significant machining errors, and the workpiece will be scrapped.

4. Parts’ technical requirements (such as form tolerances, dimensional tolerances, and surface roughness) are not marked standardization.

8 Tips for Creating Engineering Drawing

The following 8 tips will teach you how to create better engineering drawings that communicate your critical needs for the parts while also saving you time and money.

Tip 1: Dimension Only Critical & Measurable Features.

All dimensions in CNC machining can be derived from the 3D model. As a result, you should only include critical inspection dimensions and threading information on a 2D drawing.

Tip 2: Communicate Hole Tapping Needs with Thread Size & Depth.

Because thread depth is difficult to measure precisely, the depth call-out is always taken as a minimum.

Tip 3: Consolidate Call-outs If Multiples of The Same Feature Exist in A View.

Give a dimension to only one of the features in a view and name the dimension “#X DIM,”  indicating that the feature exists in the view X number of times.  For example, “6X 10-38 TAP” means 6 10-38 threaded holes in that view.

Tip 4: Communicate Assembly Intent of Crucial Features.

Provide an assembly drawing or instructions if the production involves the machining of an entire assembly. You can also offer part numbers for your machinists to look up when you want to install off-the-shelf hardware yourself.

Tip 5: Providing Part Numbers & Suppliers for Hardware Installation. 

Provide the part number and supplier on the drawing if hardware installation is needed. Simply noting “press-fit M4 dowel” provides no material information or machine shop dowel length.

Tip 6: No Need to Include Optional Secondary Operation Call-outs on the drawing.

If secondary processes like polishing and anodizing are non-critical, requesting a separate price and lead time is advisable. This way, you can know how much the additional cost and time. Similarly, if you are uncertain about the type of material to use, leave the material off the drawing to help prevent confusion in production.

Tip 7: Avoid Over-Dimension or Over-Tolerance on Your Designs.

Only a few features of a part are usually essential to its function, so you want the machinist to focus more on these features. Over-dimensioning may lose key needs in the noise, therefore only allocating tolerances to mission-critical features. 

Tip 8: Tolerance Must Fall Within Standard Accuracy Levels.

It is essential to provide the appropriate level of tolerance for your material. Don’t require tolerances below standard hand metrology tools’ accuracy capabilities. Consequently, researching the started measurements is necessary for your preferred machine shop. 

Conclusion

An engineering drawing depicts the information and requirements needed to produce a given item or product. It is a graphical language that conveys thoughts and information, not just a drawing.

Clear engineering drawing design helps your manufacturer produce a functioning and aesthetically pleasing part that fulfills your needs. At LEADRP, our experienced engineers can analyze all aspects of engineering drawings to ensure you always receive the highest quality machined parts. Contact us now and get a free quote!

References

Engineering drawing – From Wikipedia.

Engineering Drawing Basics Explained – From Fractory.