Having good drawings for CNC machining is crucial. At a minimum, drawings must be correct and contain all the information engineers and manufacturers need to fabricate a component. Beyond this, including more detailed and thorough information in designs can have additional benefits, such as saving time or even helping a manufacturer to work at a lower cost.

In this article, we’ll take a close look at designs for CNC machined parts and components. We’ll look at 2D, 3D and PDF designs, looking at what types of designs manufacturers need and what information each type of design should contain.

Key Takeaways

• 2D technical drawings are almost always needed for CNC machining projects because they display detailed information such as surface roughness and tolerances. This information is crucial to CNC machine and process selection as well as costing.
• 3D drawings aid with visualization and can be used to program machines, but they are not sufficient to produce or quote parts without detailed information such as tolerancing and surface roughness.
• Drawings must contain all necessary information and be supplied in a manufacturer-supported file format.

Table of Contents

• Key Takeaways
• What is a CNC Machining Drawing?
• 2D CNC Machining Drawings
• 3D CNC Machining Drawings
• Summary

What is a CNC Machining Drawing?

CNC machining drawings are design drawings used for manufacturing through CNC processes such as turning, bending, laser cutting or threading and chamfering. Clear and correct designs are essential for communication between designers, engineers and manufacturers.

Drawings come in 2D or 3D formats, and both types are usually needed to produce quality machined parts.

3D drawings can be fed straight into a CNC machine to be used directly for manufacture, and they also make it easy to visualize the finalized component.

2D technical drawings will contain more detailed information than 3D drawings.

• Some 3D design software allows for noting tolerancing and other details directly in the 3D drawing, but it is not as clearly displayed as on 2D drawings.
• Detailed features, such as internal threads, tolerance specifications, material specs and, in particular, surface roughness specs are more clearly marked on 2D drawings.
• 2D drawings are essential for engineers in most CNC machining projects.

2D Drawings

2D drawings are component design drawings that display vital information engineers use to correctly manufacture a component.

• They display basic information, such as the materials and finishing processes.
• They also show a component in an isometric view as well as how it will be fabricated through several highly detailed orthographic, section and detail views.
• Finally, any vital additional information needed in manufacturing is supplied as additional notes.

At Komacut, we require 2D drawings for all CNC machining projects.

PDF Files

PDF drawing files are used in CNC machining manufacturing for record keeping, version control and in approvals processes. PDFs can be created as a reference point and referred to when needed, as they are non-editable and secure. They’re often used during component quality control.

2D CNC Machining Drawings

2D technical drawings provide an isometric view for component visualization and a flat view of a component from multiple perspectives. The flat views provide all dimensional and other information required for correct fabrication. 2D drawings also provide background information and additional information, such as finishing processes.

At Komacut, we use 2D drawings for processes such as CNC turning, milling and laser cutting. 2D technical drawings display the complete information our engineers need for correct and optimal manufacture.

Key Components of a 2D Drawing

Here are the key pieces of information 2D drawings should contain.

Basic Information

2D drawings should have a title block that displays all necessary basic information about the part as well as information about the drawing itself. This includes:

• Company name, part number and drawing revision number
• Material and surface finish information
• Surface roughness requirements
• Drawing scale
• Standards used for tolerances
• The angle projection used in the drawing

Surface roughness is a measure of the texture of a surface created during a CNC machining process, quantified using measurements such as average roughness (Ra). Surface roughness should be specified in 2D design drawings.

Isometric View of the Part

Screenshot of drawing example

It’s important to include at least one isometric view of the component to help engineers and manufacturers visualize it.

Orthographic, Section and Detail Views

The bulk of the information in a 2D drawing is displayed in the orthographic, section and detail views. These are flat views that each show the component from one particular perspective.

• Orthographic views show the entire component from all sides necessary.
• Section views show a dissected view of the component and are used to display internal features.
• Detail views display detailed or complicated parts of an orthographic view.

These drawings should also show all the dimensions and features of the component and be annotated to show the fabrication processes that will be applied. A complete 2D sheet metal drawing will clearly show:

• The dimensions and details of all edges and formed features such as holes, cuts or threaded holes.
• Critical tolerances, including dimensional, angular and other tolerances.

Features

Screenshot example of threading, through holes or chamfers

Features such as through-holes, holes, threading, countersinks, counterbores or chamfers should be marked with all information required for manufacture on a 2D drawing.

Tolerances

Tolerances can be displayed for any dimension on a CNC drawing and should be detailed where necessary.

Tolerances are an important design consideration, and tolerances need to be set to ensure a component will function correctly if only minimum accuracy is achieved. It’s also important, however, not to set tolerances that are too strict. Setting unnecessarily tight tolerances will add to cost with no benefit.

Achievable tolerances also vary according to the materials and processes used. Tolerances differ between turning and milling, for example.

Show CNC turning vs milling parts for quick reference

Tolerance markup methods:

• General tolerances for unspecified dimensions are normally displayed in the title block. The title block might read, “Unless otherwise specified, all dimensions are ± 0.1 mm.” If tolerance standards are followed, these can be displayed instead.
• Tolerances for specific dimensions are displayed with the dimension they apply to. For example, a specific dimension might be marked as 50.0 mm ± 0.2 mm.

Additional Information

2D drawings should also have a section showing any important additional information. This can be instructions to deburr sharp edges, for example.

Supported File Formats

2D drawings should be supplied in a manufacturer-supported type. At Komacut, we work with industry-standard DWG and DXF files.

• DXF files are the most widely used, and almost all CAD software can import and export DXF files using a CAM or DXF plugin.
• PDF files should also be supplied for specifications and details record keeping.

3D CNC Machining Drawings

At Komacut, we normally use 3D drawings alongside 2D drawings. 3D drawings are very useful for accurate design analysis and for calculations related to design for manufacturability. They also can be used to provide highly accurate nesting which can save material usage and contribute to reducing costs.

3D models are particularly useful for components and assemblies with complex geometry.

Komacut can update your old 3D drawings to the latest version and convert 2D drawings to 3D with our 3D CAD drafting and drawing revision service.

Key Components of a 3D Drawing

Here are the key components of a 3D sheet metal design drawing.

General Information

3D drawings contain general information about the part being produced.

A title block will display information such as the name of the part, the scale of the drawing and the material the part is made from. This information will usually not be as detailed as with a 2D drawing. Crucial information, such as tolerances or surface roughness, requirements usually aren’t included.

Interactive 3D View

The key thing that 3D models provide is an interactive 3D view of a component that can be used to visualize it from every angle. This allows manufacturers to immediately see how a component will look and function when complete. This can speed up the setup process by making it easier to understand basic manufacturing requirements at the outset.

3D drawings are useful for all components, but they are particularly useful for components with complex geometry. It can be difficult to visualize complicated parts from 2D drawings alone. With 3D drawings, it is immediately apparent how a part will look and function in use.

3D drawings provide an immediate, complete interactive view of a component that can be easily manipulated.

Tolerances, Features and Detailed Information

Screenshot of drawing example

The key thing about 3D drawings is that it usually isn’t possible to display detailed technical information in them.

Most 3D drawing software only allows you to show the nominal (desired) dimension and does not allow for showing tolerances, for example. Many other features and details, such as surface roughness requirements, aren’t displayed as well on 3D drawings. The lack of this detailed information is what makes 2D drawings a necessity.

3D drawings are best for visualization and understanding basic manufacturing requirements. 2D drawings provide the all-important fine details.

When you’re using 3D software, you might find it does allow you to display details on tolerances and other features directly in the drawing. If your software offers this feature, you should use it.

Be aware that, in the absence of a 2D drawing or other tolerance information, manufacturers will use standard tolerances.

Design for Manufacturability Features

3D drawing software often comes with design for manufacturability features.

These are software features that alert designers and engineers to potential design improvements. Auto-calculations alert users to errors or opportunities to improve design. Designs can then be automatically iterated for optimized manufacturability. Without this software, design for manufacturability is a labor-intensive process.

Design for manufacturability software could identify opportunities to make tolerance requirements less strict, for example. Otherwise, it might ensure that features formed at one stage can be easily accessed at a later stage for another processes, such as welding. Otherwise, it might spot errors, such as holes located too close to bends or other features.

Instant DFM Analysis at b2b.komacut.com

Nesting Features

3D drawing software usually features nesting tools for optimizing the arrangement of sheet metal components on flat sections of sheet metal. This allows for minimizing waste in production and reducing production time, which ultimately reduces cost.

Nesting is not always as simple as it may seem. Requirements can depend on the process being used as well as factors like the number of parts being created and their size and shape.

Nesting software immediately identifies the optimal arrangement.

Machine Ready G-Code

3D drawings can be used to create a G-code that can be fed directly into a CAD machine. This allows for fast, basic programming for CAD manufacturing.

Supported File Formats

3D drawings should always be made with purpose-built sheet metal design software and supplied in a manufacturer-supported file format. Drawings should also be solid objects and not planes.

Some widely accepted 3D file formats are:

• STP (File Extension: .stp)
• STEP (File extension: .step)
• SolidWorks (File extension: .sldprt)

Note that it’s best to use STP or STEP files with 3D drawings because they are universally accepted.

Summary

• Having complete and accurate drawings is essential for CNC machining projects.
• Having both 2D and 3D drawing formats will also help to improve costing accuracy and speed and ensure part requirements are clearly communicated
• Make sure to review your drawings so you are sure your designs contain all the information they need.

2D and 3D File Reference Table