CPAP Filterbox that I built for myself

I designed and 3D printed a filterbox out of PLA (Poly Lactic Acid) for myself.

PLA is used because it is strong, easy to 3D print, and it is non-toxic. It is made from plant sugars. Lactic Acid occurrs naturally in our bodies when we exercise.

The purpose of the filterbox is to reduce the number of PM2.5 particles that I inhale while I sleep. The reason for this is explained here.

FilterBoxWrappedInPillowcaseForPreFilter.jpg This shows the filterbox connected to my CPAP machine using a 12mm ID silicon hose. There is a 13mm OD polycarbonate tube inserted into the end of the silicon tubing that exactly fits the Resmed CPAP machine. The microfiber pillowcase is wrapped around the filterbox and the tube to act as a pre-filter to capture most of the dust. This microfiber pillowcase is finer and more effective at removing dust from the air than the filters supplies by the CPAP manufacturer. It also has the benifit of being machine washable since it is a pillowcase.
FilterBoxConnectedToCPAP.jpg This shows the filterbox without the pillowcase.
PartsAsPrinted.jpg This shows what the parts look like when they come off the printer with all of the supports still in place. I have found that the support cylinder with holes in it prints just fine without any supports. The 7 supports (one center and six outer) are printed all together with supports in a single print. You will need to separate those parts and twist and pull the center hole supports out of them. The hose adapter is also printed with supports. You will need to remove the support material from that with a small screwdrive or something. Additionaly you will need to sand (150 grit) where the hose will attach to remove the very fine lines going lengthwise left by the printer. This will prevent air leeks.
AssembledFilterbox.jpg This shows what the filterbox looks like when completed. It is assembled using 7 - 5 inch #8/32 screws and nuts. The hose adapter outer ring is glused in place. The hose adapter is not shown with the 2 layers of aluminum foil tape that is commonly used for sealing HVAC ductwork. I cut half circles out of the tape and then tape the hose adapter to the top of the filterbox. using 2 or more layers of tape. Notice the notch in the hose adapter tube where the sandpaper did not sand. This is where a 2mm wide zip-tie is used to hold the 12mm ID silicon tubing in place and prevent leeks. Not shown is the silicon tubing that is attached to the hose adapter. It is a strugle to get the hose onto the adapter (about 15mm). On the other end of the hose is where the 13mm OD polycarbonate tubing is inserted. The tubing is cut into a 2 inch length. One inch is inserted into the silicon tubing which is a struggle of its own. The remaining inch exactly fits into a ResMed AirCurve 10 CPAP machine. For other ResMed machines, other hose diameters or adapters may be needed. Be very carefull cutting the polycarbonate tubing. I used a hacksaw but barely cut, then rotated the tubing and barely cut again. I repeated this over and over until the tuning was cut. I made sure that the tubing was not scratched while doing this. Afterwards, I sanded the end with 220 grit sandpaper to not have any rough edges that would be inserted into the CPAP machine. Of coarse all parts were washed with dish soap and water before using. I made sure that I did not let the parts sit in water becuase the parts may absorb water and swell up and warp. I also quickly dried the parts to prevent water form being absorbed. The last thing we want with the air filter box is for it to have ultra fine PLA or polycarbonate particles on them that will be sucked into the CPAP machine and forced into our lungs. That defeats the whold purpose of this.
FilterBoxBase.jpg This is the base of the filterbox. I will describe it from the center outward. Center support hub with a screw hole and place for center support to snugly fit. Two dents to push into the foam on the MedifyAir MA-10 Air Filter to provide a filter air lock. Six tabs that on the inside align the inner filter to the correct position, and on the outside hold the support cylinder in place. A groove that holds the support cylinder in place. Six tabs that on the inside hold the support cylinder in place and on the outside align the outer filter to the correct position. Two dents to push into the foam on the MedifyAir MA-12 Pro air Filter to provide a filter air lock. Six outer support hubs with a screw hole and place for outer supports to snugly fit.
BaseWithCenterFilter.jpg This is the base with the center filter (MedifyAir MA-10) installed.
BaseWithCenterFilterAndSupportCylinder.jpg This is the base with the center filter and the support cylinder installed.
BaseWithCenterFilterSupportCylinderAndOuterFilter.jpg This is the base with the center filter, support cylinder and the outer filter installed. As you can see, the air will pass through the outer filter, through the support cylinder and through the inner filter.
Close-Up.jpg This is a close-up of the filterbox with the screws and nuts installed and tightened. It appears to be upside down.
Filterbox-Top.jpg This shows the filterbox top. The center support with a screw hole is supported with vertical tabs that allow air to flow through and also guide the inner filter

Notes:

The screw and nut holes need to be cleaned up of any stray support fibers left over from printing so that the #8/32 scres can fit through the holes. The six outer supports are longer than the inner support. The supports have different length inner supports that extrude out each end. These supports needed to be cleaned of support material to be round without affecting the length of the outer support. I do this using a pair of pliers. I use the teeth of the pliers to remove the support material while rubbing smoothly on the ends of the outer/shorter part of the supports.

You will see after cleaning that each support has an end with a longer center portion (3mm) and an end with a shorter center portion(2mm). Perform these steps:

1. Clean all parts individually one at a time with dish soap and water then rinse and dry. Do not allow the parts to soak up water. We want to clean off all dust or particles from printing, cuting or sanding. If the parts get soaked, they may absorb water and warp.
2. Cut a peice of silicon tubing about 16 inches. Push it carefully onto the hose adapter about 15mm (after the hose adapter was sended and washed). Cable tie it into place by placing the cable tie over the slot on the tube made for the cable tie. (The section not sanded.) It is easiey to get the hose onto the hose adapter before it is attached to the filterbox.
3. Insert half of the 2 inch peice of polycarbonate tubing into the other end of the silicon tubing. If one end is rougher than the other, insert the rougher into the silicon tube. We want the smooth and straight end inserted into the CPAP machine.
4. Use epoxy to glue the hose adapter outer ring to the flat side of the top. Place glue on the rough side of the adapter ring and center it around the center of the top as best you can. Wait for the glue to dry. (24 hours). The purpose of this ring is to provide additional support for the hose adapter. Try not to get any glue on the inside of the hole in the middle of the ring. This will interfere with the hose adapter laying flat when it is inserted into the hole. Clean out any excess on the inside hole of the ring with a toothpick or paper towel while the glue is still liquid. No epoxy should be visible.
5. Place a weight on it to make sure that no air can leak under the run when it is dry. I use a bottle of speghetti sauce to evenly apply a weight.
6. After it is dry, test fit the hose adapter to lay flat inside the hole in the ring glued to the top. If some epoxy slopped in aroung the edges, you will need to sand the hose adapter outer edges at a 45° angle appropriately so that the top of the flat part of the hose adapter is even with the ring.
7. The ends of the supports with the longer center portion (3mm) should be inserted into the top. The short support goes in the center and the longer ones go in the outer support rings.
8. Then the inner filter, support cylinder, outer filter are placed on the top.
9. The base is placed with the holes approximately aligned with the supports. Starting with the center, the screws are inserted into the base/bottom and into the aligned support. This is done for the center first because it will be hard to do this with the center after the outer screws are inserted. This takes some care becuase you are simultaniously aligning 7 screws with 7 supports that are stuck in the top.
10. The base/bottom is then pushed all of the way down along with the screws until the screws pop out the other side of the top. The screws do help the remaining alignment. When the screws are all of the way through, place nuts on each of them and tighten them with your fingers.
11. Tighten the screws to completion by holding the nuts to the plastic on the top so they can't turn and tighten until snug with about a half an inch of each screw poping out the top. You will feel it with the screwdriver when the screws firmly compress the supports against the top and bottom.
12. Cut 6 peices of aluminum foil tape about 4.5 inches long. Cut out a half circle about 1.5 inches wide out of the middle of each piece.
13. Place the hose adapter flat into the hole in the ring that was glued on the top of the filter box. Use a peice of tape from the step above to tape it down with the half circles cut out laying flat on the flat part of the adapter right up against the cone part of the adapter. The tape should be pressed down on the flat part of the hose adapter, the flat part of the ring and the edges of the ring, and against the filter box top. Place a second piece of tape on the other side of the hose adapter in the same manner.
14. Place 2 more peices of tape in the same manner, but rotated around the center of the filterbox top by 120° (1/3 of the way around).
15. Place the last 2 peices of tape in the same manner, but rotated around the center of the filterbox top by 120° (1/3 of the way around).
16. Place the filterbox behind the CPAP machine. On the ResMed CPAP machine, open the filter access on the side. Very carefully with very little pressure, align and insert the polycarbonate tubing into the hole in the CPAP machine where it draws air through the filter. There should be 1 inch of polycarbonate tubing inserted into the CPAP machine and 1 inch of tubing in the hose and the hose should be pressed up against the CPAP machine.
17. Place a microfiber pillowcase over and around the filter box and wrap it around the tubing. This will be the prefilter for the filter. It is machine washable and should be washed as needed.
18. The filterbox is now ready to provide filtered air through the CPAP machine to the person using the machine. Details of how I assembled it

    I used the free OpenSCAD program to design the parts and create the 3d object files (.stl).

    I used the free program Orca Slicer to generate the gcode files used by my 3d printer.

    I used a Elegoo Neptune 4 Max printer to print the parts using Elegoo PLA plus. I set the bed temperature to 60° C. The print head was 230 ° C for the first layer and 220 for subsequent layers. Also the first layer was slowed down to 20 to 40 mm/s. I took care to make sure that the bed was leveled and calibrated properly. I also made sure that the screws and wheels were all tight before each print.

    When I printed these files, I used a 100% fill pattern to provide strength and air tightness. I have placed all of the files used for this in a zip file called Filter_Box.zip. Click on that link to download all of the files uto create the filter box. After you click on the link, look for it in the "Downloads" directory on you machine.

    In that zip file there will be a folder "UploadedToWeb". Inside that folder there will be the following directories:

    Folder Name	Contents
    ElegooNeptune4MaxGCODE	This folder contains the files that can be printed directly with a Elegoo Neptune 4 Max printer. Do not use these files to print on other printers because the print bed is very large on this printer.
    OpenSCAD	This folder contains the files that can be modified with the OpenSCAD program. You can generate STL files with these files with the OpenSCAD program which is free to download
    OrcaSlicer	This folder contains the files that can read by the OrcaSlicer freeware program to geterate the GCODE files used for printing
    STL	This folder contains the 3D Object files (ending in .stl) that can be iused by 3D printer slicer tools such as OrcaSlicer to generate gcode files used to print. For those without 3d printers, you can get these printed by finding a 3D printing service online. Just upload all of the .stl files to the website and get a quote. Make sure to specify PLA to be used becuase it is strong and non-toxic. Also make sure that you get 100% fill pattern (or as close to 100% as you can.

    Parts list links:

    Polycarbonate Tubing for Resmed AirCurve 10

    Silicon tubing

    5" #8/32 screws

    #8/32 nuts

    Epoxy to glue the hose adapter ring to the top centered on the flat side

    2mm Cable tie

    MedifyAir MA-10 Replacement Filter (inner/center filter)

    MedifyAir MA-12 Pro Replacement Filter (outer filter)

    Elegoo PLA Plus printer filament (For 3D Printing)

    Aluminum foil tape

    Microfiber Pillowcase