Project Logs

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• First Pass Through Development Cycle

  David Lesser • 03/28/2020 at 08:04 • 0 comments

  To make sure I'm happy with the overall geometry, I completed the design, including loops for elastic.  The fit is rather good on many adult faces (although I know I'll ultimately need different sizes).

  
  The next step is CNC routing an MDF mold for the vacuum former.  Since the part is 3.5" (~90 mm) tall, I needed to order some unusually-long end mills to avoid crashing the machine; I picked up a pair of extended 7/16" square-end mills and a pair of 1/4" ball-end mills (chosen largely based on what was cheap on ebay).  I'm still teaching myself 'proper' CAM in Fusion 360, but the resulting part came out pretty good:

  Next step was to our ancient vacuum former (whose manufacture was probably closer to the Spanish Flu than the current Coronavirus outbreak...), where I had fairly good results from 0.030" (0.75 mm) polystyrene. 
  

  I'm still fighting some annoying issues with seams.  It would appear that my most recent pass is my most successful, where I had the idea of reducing the heating time, making the plastic more viscous and less likely to pinch easily.  Another approach would be to change the angle of the nose cone section, from it's current 10 degrees (if I recall correctly) to something more aggressively chamfered.
  

  Last step was to the laser cutter, where my 4" (100mm) focal length lens was just barely long enough to cut the strap slots and outside profile of the mask, liberating in from the remainder of the sheet:

  Not too bad! Next step is to try to meet up with some researchers here in Tucson at the University of Arizona, who have a respirator efficiency testing rig, to determine how well it performs versus existing commercial designs.  Fingers crossed!
  

• What's an effective filter medium?

  David Lesser • 03/25/2020 at 09:06 • 0 comments

  This project is based around the not-so-obvious premise that commonly available household materials are at least modestly effective at filtering particulates from the air.  A big part of what motivated me to do this project was stumbling across papers like these, which show fairly promising results using ad-hoc materials like cotton shirt fabric or tea towels.
  

• Early success, refining the shape

  David Lesser • 03/25/2020 at 08:38 • 0 comments

  I'm new to modelling organic 3d shapes (I'm using Fusion 360's 'form' workflow), so I was happy to see my first 3d printed prototype masks are fairly good fits to my face.  I think the biggest difficulty of this project is designing a small number of different masks that will be both effective and comfortable for a large variety of people.

  Currently, I'm 3d printing shells roughly 0.050"/1.2mm in thickness to test the geometry, with an eye towards vacuum-forming using similar thickness of stock. 
  

  I've also done a first pass attempt at vacuum forming using my 3d printed prototype as a form (ultimately, I'll be CNC routing a 'proper' mold in MDF once I'm ready to commit to a design).  I don't have the right material on hand, and I don't have the best setup (as evidenced by the creases), but I've confirmed that the geometry should be moldable, as I intended.

  For the time being, I'm just drilling holes for the elastic bands in the rim.  Once I get a more certain feeling for where they should go, I'll design in some ears to keep the gasket un-disturbed.
  

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