3M filter adapter for M17 gas masks

thingiverse

Threaded adapters for M17 gas mask. Supports connecting 3M bayonet lug filters. Why? The M17 is more comfortable on me, at least when it isn't really hot. I probably don't need to say this, but using these parts will not pass any certifications and will not satisfy any compliance requirements for OSHA or anyone else. If you are intending to use this for personal protection around your home, I wish you the best of luck, but make no promises. It is very important that you do at least a qualitative test using a harmless odorant before relying on this for protection against anything hazardous. If you don't know what any of that means, you should probably just buy a commercial respirator and use that instead. Your health and safety is too important to risk on something you downloaded from the internet. If you are here for SARS-nCoV-2 protection, this should bring your old M17 up to the same level of protection that you would get from a new 3M full-face respirator using the same filters. This won't help you bypass the acute filter shortage, but if you already have filters and valves, but just want a more fashionable mask... No matter what, you almost certainly want to use the .scad file to customize and adjust the parts. This thing uses irevdev's rounded polygon library: http://forum.openscad.org/Rounded-Polygon-td21897.html This thing uses Dan Kirchner's threads.scad: https://www.dkprojects.net/openscad-threads/ This thing was inspired by thomps38's fittings: https://www.thingiverse.com/thing:3474555 Measurements were taken from a US-made M17A2 mask and a pair of M13A2 filters, I think both were 1980s vintage. The core of this is replacement "porkchop" fillers for the cheek pockets. These fillers are similar in size and shape to the original filters. They are smaller and easier to insert, while still being large enough to support attachments. These must be printed with support, in at least two places - under the top rim, and under the bottom pocket. If you are clever, you can probably block support on the threads, which will save you a little cleanup. It is pretty important that the supports are fully and cleanly removed from around the stem. This stem seals the cheek openings of the mask, so it is critical that the rubber fits tightly here. 6.0mm fits my mask, but you may need to adjust the stem_height parameter. The stem on top should be printed at 100% infill. The bottom part can be printed with 10% infill and (at least) 3 perimeters. Only the stem on top needs to be airtight, but it is a good idea if the entire intake shaft ends up tight. The inside of the stem is threaded M27-2.0, and can be accessed from the outside of the mask. The only adapter I've included so far is an adapter to fit 3M bayonet lug filters. Any of 3M's current line of filters should fit these. This part has been designed to print without support, with the lugs down on the build surface. Print this part at 100% infill. There is a threaded recess in the bottom of the porkchop. This thread is M36-2.0. The inhalation valve adapters fit here. The included adapter fits 3M # 7582 valves. The valve needs a smooth surface to seal against. The inlet valves are fully inside the sealing system, so it isn't the end of the world if they leak a little bit. Still, I print them at 100% infill. The inlet valve body needs to be threaded into the porkchops first. Once you've got it started and straight, you can use a 10mm hex key from the stem side - turn left to tighten. Or, you can use a needle nose plier as a wrench - just be careful that you don't mar the surface. Once the valve body is installed, you can insert the stem of the valve through the center hole, and insert the whole thing into the mask's cheek. One of the parameters in Kirchner's threads library is "inside" which changes the clearances. I can't get a part made with external threads to thread into a hole made with internal threads, even with the adjusted clearances. Instead, I have to undersize the male parts. 1.0mm undersize threads easily. 0.5mm is too stiff, leaving a joint that requires more force to tighten than I can apply without damage. 1.0 is a good choice for the inhalation valve bodies - the parameter inner_thread_clearance. For the bayonet adapters, you will need to tweak the outer_thread_clearance variable. It needs to be loose enough that you can install the parts, but (ideally) tight enough that they don't turn when you attach/detach a filter. If you use some sort of thread sealer, that will change things too. If the bayonet adapter is too loose, you can use the filter itself as a wrench to tighten it up when you install it Unfortunately, you can also use the filter as a wrench when you remove it, which can be very annoying. On a proper 3M mask, the inside surface of the filter's mounting hub squeezes a rubber lip against the hard plastic frame of the bayonet assembly. We merely tighten the hard plastic filter mounting hub against the printed (hard) top rim of the porkchop's stem. This appears to be good enough for me, but you should test it and add a seal if necessary. A flat O-ring with an ID of 22 or 23mm should work. This is not pretty code. I'm getting working parts out of it, but it could use some more cleanup. I normally wouldn't release it in such rough shape, but I don't believe that you will be able to get working parts without tweaking some settings. You select the part you need by uncommenting a line near the top. The porkchops refuse to render in preview mode, and full compiled rendering takes a long time. In the future, I will probably add a fitting for NATO cans with 40mm threads, Russian cans with 39.7mm threads, and possibly for a NATO gas mask hose. __UPDATED - 2020-04-07__ The combined left and combined right .STL files are one-piece porkchops with integrated 3M bayonet adapters - sized for 3mm O-rings. You still need to install the inhalation valves, but you can then feed the whole thing into your cheek pockets and directly attach 3M disc or cartridge filters with no other adapters. The lugs are positioned to correctly orient cartridge filters away from the mouth. The mask with disc filters attached still fits pretty easily into the standard-issue mask pouch. With cartridges attached, I was barely able to stuff it in and close the flap, but I don't recommend it. P026_revised.scad can be edited to adjust the fit. If you are using smaller O-rings, you'll need to edit line 16. 7.5mm is a good fit for 3mm O-rings (cross section diameter), but if you use something else, you can edit it there. Please note that a soft seal is REQUIRED there for function, so don't drop that down to 4.5mm and skip the seal unless you are using your mask as a prop. As always, stem_height and stem_dia can be tweaked to fit your specific mask. The values in the file give me a good tight seal on my mask, but yours may vary.