Filament Dry Box with Magnetic Rewinder

This is yet another filament dry box, but it has a magnetic spool rewinder mechanism.  I wanted a way to rewind the filament back onto the spool without having to open the container and introducing moisture.  I also wanted it to be as simple as possible while achieving this.

I based the overall design on Build It Make It's design as I liked the simplicity, fairly low amount of filament needed, and overall aesthetics.  It has built-in spots for a temperature/humidity display along with a holder for desiccant which makes it very easy to manage.  I did, however, change the desiccant holder by adding slits on the side walls to allow for better moisture absorption by the desiccant. I also made the cover slide-in and hold as a friction fit because the original cover would easily fall off and desiccant beads would spill everywhere.  

As you can see, the main change I made to his design was adding a magnetic re-winder mechanism.  The magnets used are ¼" diameter x ½" long cylinder neodymium magnets.  These particular magnets were selected due to size restrictions of the roller, bearings, and spool flanges.  I wanted at least 4 magnets arranged within the roller so that I didn't need to add any complicated drive train, gears, pulleys, etc. that would detract from the original simplicity of the design.  I started with some random magnets from Amazon, but they had a very weak magnetic pull and could barely rotate the roller through the cereal container.  I ended up getting N52 rated magnets with very strong magnetic pull.  N48 or even slightly lower rated magnets may work, but may slip as you wind the roller with a 1kg spool.

There is an outer sleeve for the “drive” roller (roller with the magnets) that I printed with TPU (I used 85A Ninjaflex, but 92A or similar should work too) that should grip the flange of the spools to keep them from slipping.

I also added a “drive” shaft since one bearing is offset toward the center of the drive roller and needed some sort of support for it.  This allows for the magnets to be as close to each other to maximize the contact between the drive roller and the thumb wheel.  It can be a little finicky to put the rollers in and line up the shafts to the slots in the base.  I may make some improvements to that in the future, but I thought as it's a one-and-done assembly, it wasn't that bad.

I have included all the files as STL and STP in case anyone wanted to remix or change some things (such as the holes for the magnets as the ¼" diameter x ½" long ones I used may actually be 6mm diameter x 12mm long instead.)

Parts needed:

• 1 x Digital Temperature/Humidity Sensor 
  • I liked the display for these, but you can use a different style as long as it's these rectangular style ones.
• Desiccant 
  • These rechargeable desiccant beads are great.
• 4 x 608-2RS Ball Bearings 
  • You can remove the seals and dissolve the included grease in acetone for a slightly smoother roller, but it's not necessary.
• 8 x ¼" diameter x ½" long Neodymium magnets 
  • N42 or similar magnets may work also, but I just went with the strongest N52 ones.
• 1 x Airtight Cereal Container
  • These are the same containers that Build It Make It used, and I've seen many others use the same ones.  They do have some weird geometry and since they are injection molded.  They have a slight draft angle which messed with some of the initial design, but they overall work fine.
• 1 x Push-to-Connect Tube Connector
  • This is the same one that Build It Make It used, and I like it because it allows the PTFE tube to be pushed further in.  This allows the filament to only contact the PTFE tube, and not the connector itself for reduced friction.
• PTFE Tube
  • This is the same tube that Build It Make It used, and it works well.  I mainly used it for the short section shown in the pictures with another push to connect fitting with a plug for storage.  However, when connecting the dry box to a printer, I use 3mm ID tube such as this.  It allows for much easier feeding of filament due to the 1mm larger ID.
• Optional: UHMW low friction tape 
  • This is placed on one side of the Magnet Thumb Wheel.  This reduces friction on the cereal container along with helping to hold the magnets in place.  I don't think this is completely necessary, but it does seem to help a little bit.

Print settings: 

I just used PLA+ for all the parts, except for the drive roller sleeve which should be printed in TPU.  Supports are needed for the inner shoulders of the rollers where the bearings sit, the overhangs for the temp/humidity display, and the overhangs for the magnet drive.