Mechanical drawings are perfect guides for machinists to read the thoughts conveyed by designers. These drawings use standardized symbols and language that can assist the manufacturer while making a particular part and helps to attain accuracy.
This article will introduce you to the overall concept of mechanical drawings. As a result, you’ll be able to read these drawings. Additionally, you’ll get seven practical tips to improve your mechanical drawings.
So, let’s dive straight into the post without wasting another minute.
What are Mechanical Drawings?
Mechanical drawings are a kind of engineering or technical drawings that use special instruments to explain different mechanical systems, such as ventilation, heating, and air conditioning. The primary function of mechanical drawings is to convey all the necessary information about the product’s design to the manufacturer. However, the engineers who are put on the task of mechanical drawings must concisely mention the geometric features of the required machine part to avoid measurement errors.
Usually, an engineering drawing standardizes symbols, text, layout, dimensions, types of view projections, line thickness, and descriptive geometry required for the production of a particular machine. Hence, in addition to the illustrations, mechanical drawings also help you describe the parts’ shapes and sizes. In short, with the mechanical drawings in hand, a technician can immediately start manufacturing the product by following the information given.
Methods of Mechanical Drawings
1. Manual Drawings
Manual drawing is the oldest mechanical drawing method in which drawings are made by hand with the help of different instruments, such as pencils, rulers, protractors, paper, and sheets.
2. Computer-Aided Design (CAD)
No doubt, computers have become a precious gem for mechanical drawings. Computer-Aided Design (CAD) is the latest mechanical drawing method used by various manufacturing industries nowadays. Yet, here are two subtypes of CAD used for this purpose:
● 2D CAD
2D CAD, often called AutoCAD, is typically used to create arcs, circles, curves, and straight lines. This software also enables architects to revise mistakes quickly.
● 3D CAD
The 3D CAD system is ideal for larger mechanical systems. It mainly defines the geometry of the component. With this software, you can develop section views, orthographic projections, and projected views.
Standard Features of Mechanical Drawings
The following are some basic features that contribute to the formation of mechanical drawings. Learning these components will let you know how to read mechanical drawings.
The shape of the part is essential to know how the final product will look. Geometry especially explains the object’s appearance when viewed from different angles like the top, bottom, front, side, etc. Hence, a mechanical drawing should clearly represent the geometry of the component.
Again, determining the object’s size is a crucial need for manufacturers. The designers should mention the dimensions with upper and lower limits to guarantee a longer life with less maintenance.
Tolerances refer to the extent of the variations allowed for each dimension. Typically, it is the difference between the upper and lower limits, which is usually assigned to mating parts in an assembly.
The manufacturer needs to decide on the material type before the object’s production. The material may be steel, aluminum, copper, stainless steel, ceramics, plastic, alloys, etc.
The surface quality or appearance matters a lot for a newly manufactured object. Some products demand more surface finish, while others require less. For instance, a mass-marketed object needs a higher surface finish than a part machined in industries.
In technical and complicated machinery drawings, coordinates are considered crucial. They serve as reference points when positioned along the boundaries of drawings. Therefore, they may benefit you when discussing the content of the specific mechanical drawing.
Line Styles and their Types
Mechanical drawings not only deal with similar lines; many other details can also be shown using different line styles. For instance, you may indicate centerlines and visible plus concealed boundaries of parts. Below are some types of lines:
● Continuous Lines
One of the most common types of lines is a continuous line used to draw actual objects. Its significant role is to represent a particular object’s physical boundaries visually. However, the thickness of the line may vary according to the situation. The outer boundaries generally use thicker lines, whereas inner contours use thinner lines.
● Hidden Lines
As the name implies, these lines can reveal information that cannot be seen through the naked eye in the drawings. For instance, you may find the dimensions of an internal step in a turned component with the help of these hidden lines; rather than using a cutout or section view.
● Cutting Plane Lines
The cutting plane lines are associated with the cutout view as they are used to represent the cutout path.
● Center Lines
To draw the holes and symmetrical features of a machine component, designers typically use center lines. Generally, the symmetrical representation makes the drawing convenient to read by manufacturers. Plus, the reduction of the number of dimensions makes it more visually appealing.
● Dimension and Extension Lines
An extension line is customarily used to indicate what is under measurement. In contrast, the dimension line consists of two arrowheads on opposite ends coinciding with the extension lines. In other words, the dimension line separates the extension lines as it is present in between them. Yet, the measurement is either written on top or inside the lines.
● Broken View Lines
Break lines represent the view that has been broken. The benefit of break-out is to provide the information without occupying much space. While the CNC machines demand complete views to cut the workpiece precisely. In the case of wrong measurements, the manufacturers may have to reconstruct the whole product.
What are the Different Types of Drawing Views?
Several types of drawing views are used to explain the overall design of the part. Typically, each of them offers different functions. Let’s take into account some drawing views:
1. Basic or Multiple View
The front, top, and side views are the most commonly used views that fall under the category of multiview mechanical drawings. Typically, multiview is an orthographic projection using two standards, i.e., the first and third perspectives.
In the first perspective, the view is drawn at the opposite end of the part from where the view was taken. However, in the third perspective, the view of the object is drawn next to the view position. Here is the list of some common countries that prefer different projection methods:
- Chinese Mainland mainly uses the first angle of view. The third angle of view is used only if necessary.
- The Republic of China uses both the first perspective and the third perspective equally.
- The United States only prefers a third perspective.
- Germany prefers the first angle of view. The third angle of view is used now and then.
- Japan significantly uses a third perspective, yet, the first perspective is only preferred when needed.
2. Auxiliary View
The auxiliary view is suitable for the inclined surfaces deprived of any distortions. Hence, it is not possible to represent the vertical or horizontal plane through this view.
The fundamental purpose of this view is to guarantee the true size and shape of the part by ensuring that the projection plane is parallel to the object’s surface.
3. Exploded View
Exploded views primarily focus on the relationship or order of assembly of various components in a technical drawing. By separating the parts or letting them float around the center, this type of view ensures the representation of the object in a 3D space. It typically displays the component so that it seems there has been a small explosion from the center of the product.
4. Sectional View
Sectional view enables machinists to depict better the interior of complex components, like engine blocks of automobiles. Therefore, by illustrating the interior of the part in such a way that it has been cut apart, you can achieve a section view. It is most commonly used to show the space between objects.
Best Tips for Better Mechanical Drawings
If you want to improve the mechanical drawings, you should follow the tips mentioned below:
Only draw the dimensions of critical and measurable features like essential dimensions of inspection and required threading information on your 2D mechanical drawing.
It’s tough to measure the thread depth, so make sure to treat the depth call-out as a minimum.
In the case when multiples of the same feature are present in a view, you are recommended to consolidate the call-outs. For instance, 5X 15-45 TAP shows 5 15-45 threaded holes in a specific view.
An assembly instruction must be given in an ideal mechanical drawing, especially if the manufacturing has to deal with machining the whole assembly. Alternatively, you may also assign the part numbers for the ease of machinists.
If hardware installation is required, make sure to mention the supplier and part number on the mechanical drawing.
It’s not necessary to include the non-critical operations on the mechanical drawing. You may exclude polishing and anodizing, as you may express them separately. Plus, in case you’re unsure about the material, you can leave it off the drawing. Doing so will avoid the possibility of confusion and mess.
It is crucial to attaining the appropriate tolerance level for the required material. Thus, always go for the well-researched and correct measurements.
In a nutshell, mechanical drawings are a perfect means of communication between designers, engineers, and machinists. With the assistance of the information included in the drawing, the manufacturers better understand the design intent and make the best products.
However, designers must avoid over-dimensioning and over-tolerancing as it’s the leading cause of time and money wastage.