How to Prepare a Perfect Technical Drawing

In order to manufacture or process products on CNC machines, a 3D CAD model is often required. After being loaded into the machine's memory, such a drawing is converted into G-code – this is a machine language that can be read and understood by the CNC. The device performs the necessary operations with the workpieces based on the information received. The 3D CAD file includes information about all the actions that the machine must perform in order to obtain the required part.

However, 3D CAD does not always eliminate the need for conventional, mechanical drawings. And it is very important to know how to prepare them properly, according to engineering drawing standards.

A technical drawing is a document containing a detailed 2D drawing of a sample to be manufactured. Also, this document indicates important data for production. Such documents ensure the transfer of technical requirements for the project from the designer to the machine operator.

In some cases, the machinist can produce a product without using a CNC programming on the machine. This is possible manually. As far as CNC operation is concerned, the industrial drawing is used as supplementary documentation. We will tell you why these documents are important and how to prepare them correctly.

What is a technical drawing and why is it important?

When working with CNC machines, a technical drawing accompanies and complements the 3D CAD file. Technical drawings perform several important functions:

• Dimensions, tolerances, and annotations allow the machinist to better understand what they are manufacturing.
• Drawings can display the requirements of designers.
  
• The technical drawing shows internal and external threads.

Preparation of a technical drawing is recommended even if the product to be manufactured does not have special requirements. The document will be used as a reference.

The technical drawing gives a complete picture of the details. It makes it easier for the machinist to interpret the geometry, dimensions, and other characteristics of the parts. A drawing is required if you want to produce parts with threads, tolerances, or different surface finishes in different areas.

What are the parts and types of a technical drawing?

A technical drawing includes a large amount of information. It contains the coordinates, title block, orthographic views of the product, sectional view, detail view, and a note to the manufacturer. Let's consider them in more detail:

• Title block. It is always located in the lower right corner of the drawing. The title indicates all the basic information about the part, its name, technical information (projection angle, measurement system, requirements for surface cleanliness), etc.
• Coordinates. They are needed for large and complex drawings and are a guide when reading a drawing. They are always marked along the borders.
• Orthographic views. They transmit data on the geometry of parts, dimensions of parts, and tolerances. This is a 2D representation obtained from different points of view. Hidden lines can also be included.
• Isometric view. This is a three-dimensional representation of the product in the drawing. Not always required, but it is still recommended to include the isometric view. Thanks to it, it will be easier for the machinist to understand the part's geometry, the installation's direction, and the assembly's orientation.
• Sectional view. The section is needed to display the internal elements of products that are not visible in the isometric view.
• Detailed views. They are used to display difficult-to-measure areas. Detailed views do not have to be the same size as orthogonal views; they can be placed anywhere on the drawing. Detailed views are marked with a single letter, which shows which area of the orthographic representation is detailed.

Notes to the manufacturer may also be included in the drawings. As a rule, they are indicated in the lower left corner. An alternative option is to indicate notes above the title block. They may contain additional information that was not included in the drawing. Also, the notes contain instructions for machine operators. For example, these could be deburring instructions, surface quality requirements, etc.

How to create a drawing properly?

It is very important to create a drawing correctly so that the operator understands exactly what they need to make and can read all the features of the parts. There are nine main steps in this process. Let's consider them in more detail.

• Step 1. Choose a template

There are several types of templates, such as ASTM, DIN, and ISO. They indicate the coordinates, the angle of protection, the characteristics of the title block, etc. You can also create your own template, which is convenient for you.

• Step 2. Position the orthogonal views so that they are as centered as possible

Remember that there should be enough space between them to add dimensions later. Don't use too many hidden lines, as this can make the tech drawing confusing.

• Step 3. Add the necessary details and cuts

If the part is complex and has hidden elements, then a cut is definitely needed.

• Step 4. Add an isometric view if necessary

It is not always needed, but if the product has a complex geometry, then it is recommended to add it. This will help the operator interpret the part.

• Step 5. Place the guide lines

All views can include centerlines, center marks, and section lines.

• Step 6. Add dimensions to your drawings

This is one of the key steps for creating high-quality technical documentation. They should be displayed in an orthographic and detailed view. Make sure that all dimension lines and all shapes are clearly visible and do not intersect with each other. Dimensions are also applied to the detailed and sectional views. They must be numbered.

Dimensions are the most important aspect of a technical drawing. If the client does not specify them, then it is assumed that the size is left to the discretion of the manufacturers or operators. However, in this case, it is important to remember that operators cannot be held liable for part dimensional discrepancies. We offer some tips to help you correctly determine the dimensions of the technical drawing.

1. You should always start by adding general dimensions – they are crucial for the product's end use. After that, you need to add the size to other functions.
2. Try adding all dimensions to the view from a common baseline.
3. If an object is displayed in several views, then there is no need to measure it directly in all. Instead, add dimensions to the view that most clearly describe the function.

If you need to manufacture several identical objects, you can add dimensions to only one of them. However, in this case, you must specify how many times the object appears in the current view. For example, if the drawing has five holes of the same diameter, you can specify the size next to one of them in the format, for example, 3 x ø1.5.

• Step 7. Specify the location, length, and size of all holes and threads

This is just as important as sizing because if you are planning a threaded hole, the length of the thread is an important factor. Callouts can also be used in the drawing. They are needed if you need to specify a large number of parameters for holes.

• Step 8: Add tolerances to critical functions

This is necessary if the elements require a higher tolerance than the average ISO-2768 standard. As with dimensions, tolerance plays an important role in product use. Therefore, they must be used very carefully. Several types of tolerances can be applied to technical drawings. For example, they can be one-sided, two-sided, at the intersection, etc.

• Step 9. Fill in the title block and indicate notes

Do this when the drawing is ready. The title must contain all the main and technical details. You also need to add notes and additional instructions. Once all this work is done, you need to export the finished drawing in PDF format and attach it to the 3D CAD file.