Thread by @shen

So I made a PAPR (powered air purifying respirator) over the past week in my spare time during self isolation. It was mainly to see if I could do it and ended up learning some cool new skills!

Here's a thread of the steps in designing & building this thing, with pics! (1/11)

This wasn't specific for COVID-19, would help with allergies too. I took a spare HEPA filter for my vacuum cleaner and wondered if I could make it. I bought a fan, fan controller and figured I could probably fit it in a compact box. (2/11)

I ended up deciding to use a Li-ion powerbank instead, so I could build a charging port for easy access. However with it only outputting 5V, I needed to add a step up transformer to get it to power the 12V blower fan. Here's a video of my first test after wiring it all up. (3/11)

Realising I would need a very specific case for this, I went and learnt Blender. After a lot of measuring with calipers and 10 hours in Blender, I made what I needed. It all fit snuggly. (4/11)

P.S. Blender Stack Exchange was invaluable

Next step was to get it printed. Considering the size (~200*100*70mm) it was over $500 on Shapeways, not including a buffer for me to screw up. So....I got myself my first 3D printer. The NOVA3D Elfin SLA printer. (5/11)

First, for a quick test of the 3D printer, I quickly made the connector for the tube to my mask. It printed really well, and the resin is super tough and air-tight. (6/11)

Side note: I had originally planned for this to use a full face chemical mask, but it didn't arrive in time so I used my n99 mask in the interim. These ones use a very standard bayonet mount for the filters. The design for them are already on Thingiverse. (7/11)

With the first print a success. I went ahead and printed the box. However I had to separate it into 2 pieces to fit the printer. The resin is kinda brittle so when I tried to clean up some mistakes, it cracked....nothing some superglue can't fix! (8/11)

Now to fit everything in. It was definitely very snug! But it fits and works! The fan is rated at 32CFM, more than enough to keep up with human breathing. But until now I wasn't sure how much the filter and pipe length would reduce that. (it was fine) (9/11)

The filter has a rubber skirt around it, a good seal so the only air going in was going through the filter. (ports were sealed up with glue and o-rings). It didn't go fully in because the groove I left for the skirt got clogged in the printing, still air-tight tho. (10/11)

It probably wasn't the most economical way of building this thing, but I'd been wanting to learn 3D modelling so did this project that was also timing appropriate. To do: refine the 3D model (some measurements were a few 10ths of a mm off) and hook it up to a full mask. (11/11)

Oh forgot to mention. It's a ~37Wh battery. The fan runs at 12V/0.15Ah. So at full charge, it should last around 20 hours, more than enough for a full day. The power circuit also allows it to run even when charging.

For those interested, I've uploaded the blender and stl files with a quick readme here.
The Blender file includes the objects for reference.
drive.google.com/drive/folders/…

The real mask has arrived. Can't wait to hook it up.
(The FOV is pretty great)

As requested by @OMGitsfirefoxx I'll try document the progress of the remainder of the project with more video.

Here is the end cap and tube connector for the mask, based on alphaa's cap on Thingiverse. Will get it printed tomorrow. thingiverse.com/thing:4195963

Got it 3D printed and ready for cleaning and curing! Next step: assembly.

And my PAPR is finished! Downside: none of my glasses fit inside so I'm gonna need to find a solution for that, minor issue.