40MM NATO (RD40x1/7) to 3M™ Filter Adapter

This 40 mm NATO (RD40x1/7), gas mask thread, to 3M™ bayonet filter adapter allows the user to clock filter cartridges separate from the threads, for better ergonomics and based on user preference. This is unique feature from other available threaded 40 mm adapters that direct thread on, requiring the use of shim or washers to change the clock position of filter cartridges, and do not allow the bayonet to be clocked at different positions easily. The two piece design consist of a threaded outer shell that clamps down on the inner bayonet adapter that can be clocked independently of one another. This adapter allows greater cross compatibility of 3M™ filter cartridges to full face RD40x1/7 threaded CBRN masks and other non-disposable respirators with the use of 40 mm setup adapter.

Part Description:

40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL.stl
40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL.stl
Initial release of model, initial dimensions scaled from OEM 3M™ 701 adapter.

3DPRINTER_40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL_GEN2.stl
3DPRINTER_40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL_GEN2.stl
Gen. 2 features the following changes: Resolved fitment issue with 3M™ bayonet, reduced diameter, and added additional clearance to ensure fitment for gasket. Reduced model complexity for fidelity of 3D printers: (1) removed recessed cutout for gasket to simplify 3D printing without ad hoc support, and (2) removed bottom inner shell ring protrusion for additional positive seal as smaller feature geometry may not print properly.

40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL_GEN3.stl
40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL_GEN3.stl
Gen. 3 features the following changes: changed outer shell and inner shell ODs to be backwards compatible with comparable 3M™ 701 OEM product. Also increased OAL of bayonet clearance for gasket, after feed back from 3D printing community to ensure proper cartridge fitment. [Gen 3 - Higher Tolerance Model for 3D Printers Properly Calibrated/Scaled, Outer Shell Ref. ID - 31.75/Inner Shell Ref. OD 31.70]

40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL_GEN4.stl
40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL_GEN4.stl
Gen. 4 features the following changes: Increased diameter tolerance between outer and inner parts (Outer Shell Ref. ID - 32.00/Inner Shell 31.675). And reduced bayonet protrusion OD to ensure better fitment to 3M cartrdiges per Karkoski's input. [Gen 4 - Looser Tolerance More Universal Fit, Forgiving for Printing Tolerances]

ENGRAVED_40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL_GEN3.stl
ENGRAVED_40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL_GEN3.stl
Same features as Gen. 3 just engraved.

ENGRAVED_40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL_GEN4.stl
ENGRAVED_40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL_GEN4.stl
Same features as Gen. 4 just engraved.

40MM_TO_3M_BAYONET_ADAPTER_INNER_SHELL_GEN5.stl
40MM_TO_3M_BAYONET_ADAPTER_OUTER_SHELL_GEN5.stl
After getting my hands on a physical prototype, thanks to jlwatchman, I believe this might be the final iteration. I've confirmed the conclusion of FriendsPrintOfficial, that the Gen 2 revsions features the correct underside bayonet height, although the OD of the bayonet is oversized. And have released this the final iteration after this back and forth. Due to the changes, multiple updates, I've also included a screenshot showing what dimensionally changed throughout this development.

Disclaimers/Risks:

1.) Use Proper Gaskets and Shimming Height Under Bayonet Maybe Required
Requires the 3M™ 6895 Replacement Inhalation Port Gasket, or similar gasket/o-ring, below bayonet to ensure proper seal between cartridge and bayonet. Should be compatible with 3M™ Filters 2000 Series, 3M™ Filter 7093, 3M™ Cartridges 6000 Series or 3M™ Dual Airline Systems. Note using different durometer gasket material even at the correct height on the underside of the bayonet may result in greater or less friction during engagement than original 3M™ 6895 port gasket.

2.) Perform Proper Negative Pressure Test
Follow SSPs established by your institution or workplace for further guidance. But in general, don your respirator, adjust straps till taught against face, ensuring no obstructions around the periphery of the seal against face either due from hair, facial hair, or otherwise. Exhale deeply. Cover all inhalation ports. (Typically, most full face or half face respirators have two filters, so cover those intake ports with your hands. If your running only one filter, ensure the opposite port has filter cap in place.) Now inhale deeply. The mask should suck tightly against your face without any air leakages. Re-test if adjustments are required at gasket/o-ring interfaces at the adapter.

3.) Use At Own Risk – Temporarily Solution Only Until Supply Chain Normalizes
3D printing materials are not resistant to many solvents, are water soluble, and degrade when exposed to chemicals, heat, and UV/sunlight. 3D printing this adapter is only a temporarily ad-hoc solution against biological contagions. In addition to using a properly calibrated 3D printer, due to tolerances of adapters, if possible perform hot nozzle pass on all exterior surfaces, to reduce surface porosity. Highly recommended users apply a thin layer of polyurethane clear coat on all exterior surfaces, spray or dip based methods, to help resiliency and durability for repeated sterilization and to reduce fomite transmission in printed infill layers. Once supply chains return to normal, users should purchase OEM OSHA/NIOSH/EN standard approved respirators, adapters and accessories for their institution and workplaces.

Credits

Thanks to mfxpyro for sharing the NATO RD40x1/7 gas mask threads specifications.
https://www.thingiverse.com/thing:3875269/files

And special thanks to FastIndy for local 3D printing support, adventuredepot, and jlwatchman for initial and continual remote 3D printing support, and Karkovski's feedback on design.

Dev. Notes:

03/28/2020 - Initial release of model. I’ve joined this 3D printing community to contribute to the fight against this pandemic, by volunteering my time and CAD experience in designing respirator PPE adapters to mitigate this PPE shortages. They say your greatest pain will be your greatest ministry, well nearly losing your love ones due to lack of PPE is motivation enough. Unfortunately, many PPE manufactures are currently reallocating and asking dealers to restrict the sale of respirator filters, respirators and accessories to the general public. Coupled with this shortage, hospital administrators have instructed front line clinicians to source their own PPE. With the lack of nominal protection from either surgical masks, and N95s, front line health care providers, 1st responders, and critical infrastructure staff have been struggling to find alternatives. Although more expensive, and beyond the scope of biological contagions, some have been turning to the availability of CBRN full face respirators as a viable alternative. For example, Scandinavian countries, like Finland, have been issuing wartime protective masks to emergency personnel and hospital staff. And other countries may follow this example, as MOPP gear is plentiful in many armed forces today. However, RD40x1/7 filter cartridges are typically more expensive and harder to source for private individuals than commonly available filter cartridges for non-disposable respirators from major producers at 3M, Scott, MSA, and Honeywell. And creating an adapter to fit other manufacturers filter cartridges would help to mitigate global PPE shortages as many folks already have non-disposable respirators.

03/29/2020 - Resolved fitment issue with 3M™ bayonet, reduced diameter, and added additional clearance to ensure fitment for gasket. Reduced model complexity for fidelity of 3D printers: (1) removed recessed cutout for gasket to simplify 3D printing without ad hoc support, and (2) removed bottom inner shell ring protrusion for additional positive seal as smaller feature geometry may not print properly.

04/01/2020 - Changed outer shell and inner shell ODs to be backwards compatible with comparable 3M™ 701 OEM product. Also increased OAL of bayonet clearance for gasket, after feed back from 3D printing community to ensure proper cartridge fitment. [Gen 3 - Higher Tolerance Model for 3D Printers Properly Calibrated/Scaled]

04/03/2020 - Increased diameter tolerance between outer and inner parts. And reduced bayonet protrusion OD to ensure better fitment to 3M cartrdiges per Karkoski's input. [Gen 4 - Looser Tolerance More Universal Fit, Forgiving for Printing Tolerances]

04/13/2020 - Updated with engraved markings to better ID adapters.

04/25/2020 - Gen 5, fifth iteration change after receiving a physical prototype in hand, thanks to Jeff L., was able to make final corrections. Corrected bayonet height and OD to ensure proper fitment with OEM 3M gasket and filter.