_MSA_ Mask L revisions

thingiverse

This is a refined iteration of the modular mask MSA submitted in April 2020. After experimenting with various modifications, I settled on this configuration. It combines elements from Mask L, the 80mm filter mod, and the active filter mod. The active filter mod piqued my interest because it's the only design that effectively evacuates hot, moist CO2-laden air from the mask interior. This enhances comfort, allowing the wearer to tolerate longer periods of wear. I weighed the pros and cons of positive, neutral, and negative pressure systems. Neutral was quickly ruled out since I wanted to utilize the 80mm filter mod for reduced breathing resistance, even in case the fans failed during use. Most 3D printable masks lacked sufficient clear filter apertures for comfortable breathing. A single 80mm filter module proved sufficient for this purpose. A positive pressure system is ideal for ensuring only filtered air remains inside the mask, but I tested both positive and negative pressures for comfort. Negative pressure emerged as the winner since it seemed to clear the air between breaths slightly better. The STL files provided by MSA still contained prototype features that weren't necessary, parts that weren't required by my version, and areas that could be improved to enhance airflow or facilitate eyeglasses. I utilized Tinkercad to modify/create the following components: Main Mask Body: Trimmed down the nose to accommodate eyeglasses Active Filter Mount: Removed the larger circular filter support 20mm Fan Housing: Removed bottom screw holes, added a bevel, removed in-take fan wiring slot, and shortened out-take fan wiring slot Fan Cap: Designed a minimal flat ring to hold the fan in place (replaces outer filter assembly) I opted for 5-volt CPU fans over 12-volt fans, allowing me to power the fan using a spliced USB cable and a USB battery pack. Later, I added a power pigtail disconnect to simplify mask removal. For filter material, I chose 3M Filtrete 2200 fabric. The base of the fan housing served as a template for cutting out filters, while the 80mm filter insert provided another template. Initially, I hoped to use nylon screws to minimize weight but found they lacked sufficient grip to hold the mask together. The design uses M3x8mm button head hex screws to secure the mask mounts and fan cap and M3x6mm button head hex screws to secure the headbands. (I didn't employ the spacers included in MSA's original design.) Except for the mask body and 80mm filter body, all components were printed without supports or brims at fine resolution (0.1mm) with 1mm walls and 20% cubic infill. The 80mm filter body was printed (0.1mm/1mm/20% cubic) with supports and a brim. The main mask body was printed as offered by MSA at fine resolution, without supports, with a brim, 2mm walls, and 20% cubic infill. I added a 3/8 inch wide by 3/16 inch thick weather seal strip across the bridge of the nose and tops of the cheeks for improved air sealing and comfort. My initial test prints were done in black PLA at lower resolution. However, living in a very hot and dry climate, I was concerned about PLA's heat resistance. Therefore, I printed my final masks with PETG. In use, I've worn this mask numerous times for periods exceeding an hour. I extend my gratitude to MSA for offering the original mask.