Hello everyone, I wanted to write a blog that may help some of you during this difficult time. Due to the Coronavirus disease (COVID-19) there is a lack of PPE gear around the world. This shortage is putting our frontline workers at risk and we absolutely need them to stay healthy. There are also members of the community that are at risk or asymptomatic and spreading the virus. What you will see in this blog is a possible method to help in the effort to keep the public and healthcare workers safe. I will show you one possible method for making a homemade mask for yourself. This design may potentially aid in reducing leakage around an individual’s homemade mask as well. I will be providing files that can be downloaded. Please feel free to make modifications to the file/files for better fitment. Note: The main purpose for the public to wear masks of any kind is to protect others from being infected by the wearer, thus reducing the transmission of the virus by egress (transmission of particles from the wearer to the outside environment) since many people appear asymptomatic.
Disclaimer: This mask has not been through the proper testing to ensure protection from any pathogens, it makes many assumptions based on the available data. This is not a replacement for PPE that meets guidelines and regulations issued by the CDC, WHO, and government agencies. Please follow the recommendations from your health officials and follow social distancing rules as the best way to protect yourself from the COVID-19 virus.
The first thing I did for this project was to gather information on the effectiveness of different materials in filtering and reducing the spread of pathogens. I read multiple articles and am including only those that provide the most relevant data for this endeavor (I will include links for those studies and other relevant information below). Based on those scientific studies, I think we can make some design decisions that will get us something that will offer at least some protection. By making our own masks we will help ensure that our frontline workers (healthcare workers, EMTs, EMSs, etc.) are the first ones to receive NIOSH approved PPE and we aren’t accidentally siphoning critical resources away from them. The other important aspect of this blog is that I will be showing a reverse engineering workflow. This is just one possible method for reverse engineering, but it may give you some new tools in the process.
When I first heard about the mask shortage, I thought that there had to be a way to 3D print a mask or parts of a mask to help fill supply needs while the traditional supply chain was getting ramped up. This would allow for End-Point Production or close to it. Shipping is either eliminated or at least reduced. The other factor that I knew would be important was the ability to 3D print a high volume of masks. I saw online that some other people had designed 3D printed masks, but the designs would take a fair amount of time to print. I wanted something simple that would be easy to produce and use readily available materials. I was also lucky in that I had an old respirator from a project lying around. I looked at the respirator for inspiration and decided to deconstruct the most important aspects of the design. This led to pondering if I could just 3D Print the flat portion of the mask and use filter materials for the rest. I used this concept to drive my design.
The next step was to start reverse-engineering the mask for my intended purpose. I took my mask to my photocopier and made a copy of the flat portion of the mask.
This gave me a nice flat image with a scale of 1:1 (note: I could have also scanned it). I could now pull some rough dimensions off this flat layout. Then I can either scan this photocopy or take a picture of it and import the .JPG file into SOLIDWORKS. Once I had the .JPG file imported I then needed to scale it.
Now I can now start using the image to guide my sketch entities. Once my sketch is complete and fully defined (Fully Define Every Time), I can extrude it.
At this point, I determined that I was unhappy with the design and did not think it would work how I intended. In flattening the mask down against the copier glass, it reduced the arc of the nose ridge. I felt this would not only be uncomfortable for the end-user but also cause leakage between the mask and my face. Based on the information I read in the scientific articles’ leakage was one of the biggest issues for allowing pathogens into mouth and nose.
Time for a slightly different approach.
This time I used my phone to take pictures of the respirator and import them into SOLIDWORKS. The command for bringing in pictures is called Sketch Picture. Once the picture was imported, I scaled it, located it, and rotated it to my desired position.
Then I performed the same steps as above. I sketched the outer perimeter and the inner opening.
Then I extruded the outer perimeter sketch followed by an extruded cut for the inner opening.
Next, I sketched slots for the attachment points where elastic bands or ties would be used. I then extruded cut those slots.
Then I applied the Fit Spline command (make sure to select all the sketch entities that make up the face, pro tip – right click on a line and use the select chain option) to smooth out the faces for the Overall Extruded Body Sketch, the Internal Opening Sketch, and the sketch for the slots.
I then applied the fillet command using the full round option for the outer face, inner face, and the faces for the two slots. The Full Round Fillet for the exterior face is shown below (Side Face 1 is Light Blue, Center Face is Magenta, and the Side Face Set 2 is Light Pink).
This was followed by using the mirror command to apply the two slots with fillets to the opposite side of the mask. The last thing to do now was to generate a file for the 3D printer. I could generate an STL but many platforms can also use the newer 3MF format. I generated a 3MF file using the new SOLIDWORKS 2020 capability to print directly to a printer. The command is named Print 3D and can be found underneath the File dropdown menu. I chose the option for the Stratasys F370 and it showed me the build volume of the machine and gave me some options for setting up the print. It also gave me three different file formats that I can save out.
I saved out my 3MF file and sent it and my CAD files to my buddy Dan Erickson (shout-out to Dan, he is a great engineer and our Team Lead in the Printed Parts department). Since Dan specializes in 3D Printing, he can provide valuable feedback on my design and catch any possible issues that may occur based on my current design. I can use his feedback to modify my designs if necessary and send him updated files that will print nicely. We are planning on using PLA for our first print. We know that this is a widely used and readily available material in the 3D Printing Community. This will ensure that the maximum number of people will be able to use this design. We want some flexibility from the material for this design and we recognize that PLA is rigid, but we will control this through-thickness and geometry.
Now I am lucky that I have access to 3D Printers through our offices but what is beneficial for everyone is our printing services department can print for you as well. All you need to do is submit the file/files that you would like to get printed and they will contact you on the details and provide a quote. This is a great resource if your company is not ready to buy a 3D Printing machine yet but could still benefit from its capabilities. At this point, I am looking forward to having my printed parts in hand so I can start experimenting with different filter materials. I would like to discuss filter materials before we end the blog article. I have seen some mask designs where people are using HEPA filters. Based on the information provided by 3M & Filtrete, they do not want people using HEPA filters for this purpose. This is directly from their website, “Our filters are designed to be used in HVAC systems, and the filter media has not been tested to be used as a face mask for respiratory protection. Altering any of our 3M Filtrete™ Air Filters is not recommended or supported by 3M or the Filtrete™ Brand. Customer safety is our number one priority.” (Link provided below). Using this information and the information in the research articles I am going to start with tea towel material. If I can get more information from Filtrete I may try and use a non-fiberglass air filter. I hope everyone learned some useful design tips in the article! Please check back for updates on this project. So long everyone and stay safe out there!
Please check the configurations tab for the SOLIDWORKS file below. There are 3 different sizes that you can pick.
- [ARTICLE] Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?
- [PDF] Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population
- [ARTICLE] 3M/Filtrete: Coronavirus and Important Things to Know About Airborne Particles
- [ARTICLE] 3M/Filtrete: Healthy Living Filters
- [ARTICLE] CDC Use of Cloth Face Coverings to Help Slow the Spread of COVID-19
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