How to Create Professional CAD Drawings for Patent Applications

Patents are a type of intellectual property that protects inventions. They are awarded after an application process often laid out in a country’s patent law and/or regulations and are valid for a non-renewable period of 20 years from the filing date. Most patent laws, from the UK’s Patents Act 1977, the Patent Law of the People’s Republic of China, and US Code: Title 35 (35 USC) to Japan’s Patent Act, Korea’s Patent Act, and India’s Patent Act, require applicants to submit patent drawings alongside other documents during patent applications, subject to certain conditions. 

Although not always mandatory, these drawings visually depict the subject matter and clarify the scope of the claim being protected. They also offer other benefits, which we discuss below. That said, you cannot just upload any drawing as part of the patent application process. This is because each patent office has several requirements that you, the applicant, must comply with when preparing your professional CAD drawing for patent application.

Today’s article delves into patent drawings and their benefits, the requirements for patent drawings as laid out by various patent offices, and the best practices when creating CAD drawings for patent applications. We also discuss how you can convert CAD files to the most preferred patent-ready file format, PDF. Lastly, we explore the considerations you should make to ensure compliance with patent laws and regulations. Let’s get started.

Patent Drawings and CAD Drawings for Patent Applications

Why is a Patent Drawing?

Patent drawings primarily help examiners and others understand the subject matter an applicant wishes to patent. However, in some cases, the drawing may not be necessary. For instance, you may not furnish a drawing if, when applying for a utility patent, other documents provide all the details related to the subject matter. 

However, according to the 35 USC, a drawing is necessary in cases where it is referred to in the patent specification. (A patent specification includes the title and background of the invention, a brief description of views of the drawing, a detailed description of the invention, an abstract, and at least one claim). If the applicant does not furnish such a drawing, an examiner will prompt the applicant to supply it as part of their reply to this requirement. In such an instance, the drawing may be an ink sketch or a permanent print of a drawing. These can include drawings created using CAD software such as AutoCAD, SolidWorks, LibreCAD, or SketchUp.

Generally, the CAD drawing for patent application is filed alongside other documents like patent specification, executed oath or declaration, fee transmittal form, application transmittal form, and more. This CAD drawing contains the following:

• An illustration of the subject matter to promote understanding of what is to be patented and/or
• Illustrations such as diagrammatic views, figures, and flow sheets in cases of processes

Functions of Patent Drawings?

Patent drawings and CAD drawings for patent applications offer the following benefits:

1. Patent drawings provide a visual representation of the subject matter and clarify the claim’s scope (providing visual evidence of the product’s novelty and usefulness), thus supporting the descriptions contained in the specification/other documents
2. One of the views of the CAD drawing for patent application is used, upon patent granting and publication, to best illustrate the invention to the public
3. The patent drawings provide a basis upon which attorneys can prosecute infringements 
4. CAD drawings assist examiners, the public, and competitors in comparing inventions and identifying distinctions between references

Understanding the Requirements for Patent Drawings

National intellectual property/patent offices and the World Intellectual Property Organization (WIPO) each have regulations governing the patent application process. These regulations serve as guidance for both applicants and examiners. They outline, among others, the types and specifications of documents, including how to prepare your CAD drawing for patent application. These requirements also provide information that helps examiners as they search and examine the patent. The Patent Cooperation Treaty (PCT) regulations outline the following requirements:

• Guidelines for Examination in the European Patent Office (EPO)
• WIPO’s Regulations under the PCT 
• The United States’ Electronic Code of Federal Regulations: Title 37 – Patent, Trademarks, and Copyrights (37 CFR)
• The UK Intellectual Patent Office’s Patent Factsheet for Drawings
• India’s Patent Rules 2003
• Australia’s Patent Regulations 1991
• Regulations of the Patent Law of the People’s Republic of China

Regulations Under the PCT

Applications filed under the Patent Cooperation Treaty must conform to certain requirements. The PCT currently binds 158 contracting states. It makes it easier than ever before for applicants to seek patent protection for their invention simultaneously across signatory states by filing a single international patent application and then subsequently filing national patents in each jurisdiction. Such an application is generally filed with the patent office in the applicant’s home country or at the International Bureau of the World Intellectual Property Organization (WIPO).

The regulations under the PCT have the following requirements:

• The scale should be represented graphically when, in exceptional cases, the scale is given in the drawing
• Use A4-size sheets (29.7 cm by 21 cm)
• Minimum margins of 2.5 cm at the top and left side of the paper, 1.5 cm on the right side, and 1.0 cm on the bottom are recommended, meaning the surface usable must not exceed 26.2 cm by 17.0 cm
• Execute the CAD drawing for patent application in black, well-defined, sufficiently dense, and uniformly thick strokes and lines without colorings
• Use oblique hatching to indicate cross-sections
• Scale the drawings appropriately to ensure the features are still distinguishable when the drawing is linearly reduced to two-thirds
• Draw all the lines with the help of drafting instruments like CAD software
• The height of numbers and letters should be greater than 0.32 cm
• You may include multiple different figures on the same sheet in an upright position and without wasting space
• Number the figures consecutively using Arabic numerals; number the sheets in a similar manner, albeit independently

Other requirements can be found here under section Rule 11.

EPO Requirements

The EPO’s guidelines on the presentation of drawings include the following provisions governing the form of patent drawings: 

• Drawings and other documents must be filed in a single copy and must be of a quality that permits reproduction
• Paper documents must be on strong, pliable, white A4 (29.7 cm by 21 cm) paper
• Minimum margins (2 cm at the top, right, and bottom and 2.5 cm on the left) and maximum margins of 4 cm at the top and on the left side and 3 cm on the right side and bottom
• You should not add any handwritten copy to the text
• Use minimum character height of 0.21 cm for capital letters (font size 9 or 10)
• All sheets must be numbered in consecutive Arabic numerals
• Drawings should not be colored and should feature durable, black, sufficiently dense and dark, and thick lines and strokes
• Use hatching to indicate cross-sections
• Scale the drawings in such a way that permits reproduction and allows for all details to be distinguished when the size of the drawing is reduced to two-thirds
• The numbers and letters should be greater than 0.32 cm in height
• Do not include text in the drawings 
• You can include several figures in the same sheet of drawing

USPTO Requirements

The US’s CFR 37 contains separate requirements for plant patent drawings, design drawings, international design reproductions, and reissue drawings. For instance, design drawings must contain a sufficient number of views that comprehensively show the appearance of the design; this requirement may not apply to other types of drawings. Nonetheless, all drawings must conform to the following universal requirements:

• Views can include exploded views, sectional views, partial views, alternate positions shown by a broken line superimposed upon a suitable view, or modified forms of construction shown in separate views. 
• Number the sheets and views in consecutive Arabic numerals
• Use identifying indicia, which should include the inventor’s name, title of the invention, and application number
• Solid black surface shading is prohibited except when used to represent the color black
• Applicants may use broken lines to show visible environmental structure; the broken lines may not be used to show hidden surfaces and planes
• Alternative positions of a design component drawn in the same view are prohibited
• Do not combine ink drawings and photographs
• Use black and white drawings, although color drawings are permitted
• All drawing sheets must be the same size (either 21.0 cm by 29.7 cm or 21.6 cm by 27.9 cm)
• Each sheet must include margins of at least 2.5 cm at the top and on the left, a right-side margin of at least 1.5 cm, and a bottom margin of at least 1.0 cm
• Use a large enough scale that shows the mechanism of the design without crowding when the drawing is reduced in size to two-thirds in reproduction
• The drawings should include features, e.g., the size, weight, and thickness of characters and lines, that make them reproducible
• Use graphical drawing symbols when appropriate
• Add descriptive legends subject to approval by the USPTO (The US Patent and Trademark Office)

UK’s Patent Factsheet for Drawings

According to the UK Intellectual Property Office (IPO), patent applicants can include any drawings to illustrate the description of their invention. And while this isn’t a mandatory requirement, the IPO provides a Patent Factsheet for Drawings that explains how to prepare said drawings. The fact sheet lists the following requirements:

• The patent application should include a set of good-quality drawings that illustrate different views of the invention or product
• The drawing should illustrate the product from different angles and, if possible, include cross-sectional views
• Include figures of key features that would be hidden during use
• The drawing must feature black, well-defined lines to promote reproducibility
• You can include multiple drawing sheets; each sheet should be numbered (preferably indicating the total number of sheets in the drawing, say, 1/3)
• Each sheet may contain several clearly labeled figures
• Use capital letters that are greater than 0.3 cm in height
• Leave margins of at least 2 cm at the top and left-hand side, 1.5 cm on the right-hand side, and 1.0 cm at the bottom
• Prepare the drawings on white A4 paper
• The drawings should not show dimensions or materials
• Excessive shading and the use of colored inks/paper is prohibited

India’s Patent Rules

Rule 15 of India’s Patent Rules 2003 stipulates the provisions that drawings must fulfill. They include:

• The patent application must include other documents alongside the drawings
• The drawings shall be on standard A4 size paper
• The minimum margins are 4 cm at the top and left-hand side and 3 cm at the bottom and right-hand side
• The sheets should be numbered, with each CAD drawing for patent application bearing the name of the applicant (in the left-hand top corner)

Preparing CAD Drawings for Patent Applications

Preparing CAD drawings for patent applications is straightforward thanks to standardized guidelines provided by patent offices worldwide. So, it’s always just a matter of following the set rules. It’s, however, vital to bear in mind that the requirements vary from one patent office to another. Here are a few considerations and best practices you should make when preparing your CAD drawing for patent application:

Black-and-White and Color Drawings

Some patent offices, like the USPTO, accept colored drawings. But there’s always an unsaid caveat: reproducibility. These offices require applicants to submit high-quality drawings that can be reproduced through scanning, photographing, or printing. And given that colored lines often appear faint when reproduced in black and white, it is advisable to stick to black and white from the onset. In fact, the EPO proves the importance of this approach, noting that while color drawings can be submitted, they will be scanned, printed, and availed in black and white only.

Figures and Views

The CAD drawing for patent application must include as many views as necessary to adequately show the subject matter of the invention. The CFR 37 requires applicants to include one of these views on the patent application publication and patent to best illustrate the invention. 

Using multiple views naturally results in plenty of figures. In cases where a single sheet features multiple figures, each figure must be numbered consecutively in Arabic numerals. The numbering should be preceded by the word ‘Figure’ or the abbreviation ‘FIG/Fig.’ The EPO requires applicants to use FIG, while the USPTO mandates the use of Fig. On the other hand, the UK’s IPO requires the use of the word ‘Figure.’

Types of Views

You can use any of the following types of views:

• Plan view: This view shows a top-down view of the invention.
• Elevation view: This view shows one side (left, front, right, or back side) of the product, as in the image below

Different Views for Use in CAD Drawing for Patent Application (source)

• Sectional or cross-sectional view: This view should only be used to clarify the disclosure and to minimize the total number of views used. It should not be used merely to show the internal layout of the invention’s mechanical features because this may result in confusion relating to the scope of the claim.
• Perspective view: This view represents a product just as it is seen by the eye
• Exploded view: This view is intended to show the relationship or order of assembly of different parts. It serves as a supplementary view to the fully assembled view.
• Partial view: This view is used to represent broken-up views of a large machine or device that may not be intelligible if wholly illustrated on a single sheet. The partial views can be placed on a single sheet or extended over multiple numbered sheets. Nonetheless, a small-scale view of the large machine should be included and should indicate the positions of the parts/portions.

Shadings and Hatching

Shading shows the contour or character of the surface of a 3D object. It helps examiners and other parties to understand the drawing. You can use different types of surface shading. The two commonly used types of shading are straight-line shading and stippling (which uses a cluster of dots). 

The USPTO discourages applicants from using multiple types of shadings together on the same surface. They can, however, be used on different surfaces on the same CAD drawing for patent application. Moreover, the shading should not be so excessive that it impedes legibility; for instance, solid black surface shading is prohibited save for cases where it is used to represent the color black.

Cross sections are also hatched with regularly spaced diagonal/oblique lines. The EPO allows you to choose the space between these lines based on the total area to be hatched. The hatching should not hide certain aspects of the CAD drawing, including leading lines or reference signs.

Illustration Showing Oblique Line Shading (source)

Line Weight and Character Size

The EPO, WIPO, and IPO require applicants to execute the drawing in black. This requirement restricts you from using colored inks. Additionally, the thickness of lines must account for the scale, execution, and perfect legibility of both the CAD drawing for patent application and reproductions. The lines must be drawn using CAD software or drafting instruments, except for irregular diagrams and structures. 

You can use broken lines in US patent filings to show visible environmental structures. Additionally, you can use broken lines to highlight parts of the drawing that are not considered part of the claimed design. However, these broken lines may not be used to show hidden surfaces or planes that cannot be seen through opaque materials, as they may interfere with the clear understanding of the claimed design. Another USPTO rule is that oblique line shading (as shown in the image) must be used to show translucent or transparent surfaces and reflective or polished surfaces like mirrors.

Arrows and Lead Lines

Lead lines are lines between the reference characters and the details the characters refer to. These lines should be as short as possible and can be straight or curved. Additionally, they must begin immediately next to the reference character and extend to the feature indicated. They must never cross each other.

On the other hand, arrows in CAD drawings for patent applications are used as follows:

• In sectional views to indicate the direction of sight
• To show the direction of movement
• On lead lines to indicate the entire section towards which the freestanding arrow points
• On lead lines to show the surface

Symbols

Some patent offices allow patent applicants to optionally use graphical drawing symbols for conventional elements when appropriate. However, the applicants must adequately identify such symbols in the specification. In cases where the symbols represent known devices, the applicant should use universally recognized symbols with conventional meaning. Symbols that are not widely recognized may be used, subject to approval by the patent office. However, their use is restricted to instances where they are unlikely to be confused with existing conventional symbols.

Legends

Legends are meant to provide more information about the CAD drawing for patent application. However, some requirements restrict the use of legends, requiring prior approval by the patent office. The US’s CFR 37 notes that legends should contain as few words as necessary and may be used subject to approval by the USPTO.

Best Practices for Professional Patent Drawings

Now that we have discussed what to keep in mind or do when preparing a CAD drawing for patent application, it’s time to delve into how to present it. In this section, we will look at rules that govern the size of the paper (which helps you come up with the correct scale), the scale, margins, appropriate views, indicia, numbering, and much more.

Scaling

The general rule of thumb is choosing a scale that will enable all details and features to be easily distinguished and without crowding when the CAD drawing for patent application is linearly reduced to two-thirds. If the figure in the drawing is not intelligible upon linear reduction, splitting it into partial figures is advisable. You may ask yourself when such a reduction is necessary, and the answer is when the drawing is photographically reproduced, i.e., when a photo of the drawing is taken. The size of the paper also determines the choice of the scale. Combined, these factors should help you determine the correct scale.

Margins

Margins vary from one patent office to another. For instance, the USPTO requires margins of at least 2.5 cm at the top and on the left, a right-side margin of at least 1.5 cm, and a bottom margin of at least 1.0 cm. On its part, the EPO requires minimum margins of 2 cm at the top, right, and bottom and 2.5 cm on the left. The margins should, however, not exceed 4 cm at the top and on the left side and 3 cm on the right-hand side and bottom. We, therefore, recommend that you go through your national/regional patent office’s requirements. That said, it is worth pointing out that, universally, the margins should be free of text or drawings.

Paper Size

Most patent offices around the world require that the CAD drawings for patent application be submitted on A4 paper size. This requirement applies to both mailed-in documents and electronically filed documents. 

Sheet Numbering

Drawing sheets should be numbered in consecutive Arabic numerals, starting with 1. The sheet numbering should be independent of the figure numbering.

File Format

Patent offices generally accept DOCX or PDF files. In some instances, you can submit both. The EPO and UK IPO accept PDF files. In the US, you can submit DOCX or PDF files, with PDFs being the preferred mode for design patent applications. 

WIPO accepts the following file formats: DOCX (which is immediately converted to full XML using the Application Body Converter), PDF documents (which must meet specific requirements), and TIFF and JPEG image files. The maximum file size for any document uploaded on WIPO’s ePCT electronic filing platform is 20MB. 

Converting CAD Files into Patent-Ready Formats

The section above clearly shows that the PDF file format is the most preferred patent-ready format. But there are a few considerations to make. Firstly, the file’s page size should be A4, black and white, have a resolution of 300 dpi, and be compatible with a particular version of the PDF standard. Against this background, do convert your native or non-native CAD file to PDF, bearing in mind that the converted file should conform to the requisite margins among other requirements listed above.

AutoCAD enables you to convert DWG to PDF. Other CAD software also enables you to save drawings as PDF files. For instance, Creo lets you export a CAD drawing for patent application to PDF. The Creo’s PDF Export Settings allow you to set the color, resolution, drawing sheet range, line style, and more. SolidWorks also lets you save drawings as PDFs by clicking 2DPDF on the home ribbon or File > Publish > 2DPDF. You can also save FreeCAD drawings as PDFs. 

You can also use non-CAD software or tools like Adobe Acrobat and online PDF converters. Adobe Acrobat lets you convert AutoCAD DWG files to PDF. While other online converters may be an option, they may not be well suited for the task. For instance, such converters may make it impossible to select your preferred version of the PDF standard. They may also prevent you from modifying certain settings, like the resolution, color, etc. In this regard, sticking with CAD software or Adobe Acrobat may be the best option.

Legal and Compliance Considerations

Navigating patent law may be a tad complicated for people without a legal background. You need to comply with not only the law but also the regulations/rules that support the law. The issue compounds if you want to file for a patent in multiple jurisdictions. While the WIPO PCT may have made such an application more manageable, it is not as straightforward as it may sound. (WIPO makes it easy to file a single international patent application that then forms the foundation for national filings in each jurisdiction. For these reasons, here are a few considerations to make when applying for a patent:

1. Work with a Patent Attorney or Patent Agent

Patent attorneys have a law degree and a certain level of expertise in sciences and technology. On their part, patent agents have a degree in sciences or engineering and are well-versed in patent laws. This means that agents have more technical expertise than patent attorneys. This, coupled with their lower salary requirements, informs companies’ decisions to use the services of agents rather than attorneys.

Patent agents help applicants to interrogate the patentability of their inventions, draft specifications, complete requisite forms, conduct initial searches, lodge applications, and follow up on issues that may come up. Usually, applicants seeking patents in other countries will use patent agents registered in those jurisdictions. On the other hand, attorneys can do all these tasks in addition to litigating disputes before the patent office or civil courts and providing legal counsel. To ensure compliance with the law and regulations, working with a patent attorney or agent is crucial.

2. Comply with Patent Rules and Requirements

Some of the patent rules are pretty straightforward, even for laypeople without a legal background. For instance, it is easy to establish the margins, character heights, color, shading, and other requirements you should meet when preparing your CAD drawing for patent application. And we believe this article has even made it easier to get ahold of this information. However, in cases where some rules are vague, an agent’s or attorney’s expertise can prevent you from unnecessarily muddying the waters.

3. Non-Disclosure Agreements (NDAs)

In instances where you want to share information about your unpatented invention, perhaps with potential collaborators, an NDA may help promote confidentiality. The NDA is necessary because sharing such ‘new’ information can constitute premature publication, thus affecting patentability because it erodes novelty. To prevent this, you can have your collaborators sign NDAs prohibiting them from sharing information about the invention until, for instance, your patent application is successful. The NDA essentially serves as a commitment to confidentiality.

Conclusion

Patents offer exclusivity for 20 years, allowing inventors and companies to commercialize their inventions and, perhaps, recoup their research and development (R&D) costs. But to enjoy the exclusivity that patents grant, inventors must first file a patent application describing their respective inventions. The application often includes various documents and, if applicable, drawings. The CAD drawing for patent application has to conform to various requirements that help support countries’ patent laws. 

These requirements touch on such elements as margins, line weight, permitted views, use of colors, shading, paper size, and more. They also outline requirements that govern other application documents, too. Going through these rules, as well as the patent laws, can be daunting for inventors without a legal background. For this reason, it is advisable to work with a patent agent or patent attorney to help you navigate this journey. And if you wish to share your invention with other parties, it should not be lost on you that that constitutes premature publication and can affect the patentability of your product. Therefore, always consider sending NDAs to such parties.