I came across ROWAN.EDU's 3D filter mask and thought it fit well but I didn't like the filter plate (they've since updated it and it's now a bit better). I had already printed out some of Maxdarkdog's filters for a full face snorkel adapter on a previous project so I figured I'd try and adapt those to this mask. I liked that his filters used standard cotton makeup remover pads as filters and since I had a whole bag of them (and not much else) it was a no brainier for me. I also believe the adapter will work with real 3M filters so it seemed like a doubly good idea. (My English Prof would be so proud right now..)
I used Rowan's mask insert as a template and replaced the grid holes with a single stand-off filter adapter. That led to a dual "V" tube adapter which quickly led to simple "T" tube and then at last, a "T" tube with slightly upturned ends - for ascetics only although it would allow me to bring the filters a bit closer if I want.
I've included ROWAN's original files (please checkout their site as they update their designs and may have even better ideas that might fit your needs better - again, I have the cotton rounds so it makes more sense for me to use these), Maxdarkdog's (great job by the way!) files and my customized filter attachments.
The single filter adapter printed well straight up on the print bed but the Y, T and T variant had to be printed on their side with some minor supports.
The filters fit snug on the adapters without the need for a gasket but the square insert into the mask has a little play (it's supposed to have a piece of cloth around the edges to keep it snug and act as the filter in Rowan's original design. Once I found the adapter I liked (angled "T") I dropped in a bit of epoxy to the insert and once it cured it's airtight (and no longer smelled like epoxy!). Works great!
The single filter attachment was fastest/easiest to print but it didn't breath as easy as the others. Using two filters makes breathing much easier and there's no longer any blow-out around the mask edges so there's an added benefit that my glasses not fogging. All in all it means I'm also going to use this around the shop!