DIY Filament Dry Box (Simple + Cheap)

Edit 2023-09-15: Removed PC4-M6-Extruder-Mount because I realized it's completely unnecessary (lol). The PTFE tube from the box rests against the extruder, which works just fine.

Edit 2025-05-14: Updated recommendation for clear silica as orange does not indicate early enough. Added more information on hygrometers, including weighing desiccant to determine weight, and desiccant drying.

Outline

I wanted a way to store my filament in a dry environment and print directly from storage without constantly having to move spools around. I couldn't find one for a reasonable price, so I built one.

This design can store and dispense 4 spools of filament at once, keeping them all in <20% humidity (if my cheap hygrometer is to be believed). Switching filaments takes an extra 30 seconds, but it's worth it to keep my filament dry.

I ended up spending about $40 on this project (for context, that's about the same as a cheap Amazon filament dryer that only holds a single spool). Depending on what you have laying around, this may be a little more (total cost of materials is about $50) or significantly less. I chose an IP67-rated box, which is probably overkill. You also don't have to buy a hygrometer if you use indicating silica gel.

Here are some similar designs you may want to check out:

https://www.printables.com/model/858-6-spool-filament-dry-box-storage-system-with-bowde

https://www.printables.com/model/268604-husky-ip65-moisture-proof-4-spool-filament-dry-box

Both are more expensive/complicated than this design but have certain benefits and are definitely worth a look.

This also works with bearing-mounted spool rollers, my take on which is here.

Assembly

Bill of Materials

The quantity of pneumatic fittings and 3D printed parts depends on whether or not you are making the PTFE tube attachment for the printer side.

Do NOT buy blue silica gel desiccant beads. They contain cobalt chloride which has been banned by the EU for its toxicity. It is still available in the U.S., but orange silica gel is considered safer. (Still can't eat it, though.) In mine and others' experience the orange indicating beads do not change color until the humidity is quite high. Recommend clear beads as they carry less health concerns and perform equivalently.

You can get reasonably accurate hygrometers for quite cheap. Digital and analog are available; both should be calibrated! I used an analog hygrometer because I could get one for slightly cheaper and I'm bad at remembering to change batteries.

(To calibrate a hygrometer, place it in an atmosphere with known humidity for about 24 hours and adjust to match known humidity. If you have a hygrometer you trust you can use that as a data source. Otherwise, a sealed container with a small amount of table salt and water mixed together to form a slurry will create an atmosphere with a humidity of about 75%.)

Assembly Instructions

Mounting spools in the box:

1. 3D print 2 inner rings and 2 outer rings.
2. Procure a box and decide where to position your PVC pipe in the box. I put mine slightly above the vertical center, but centered horizontally and level.
3. Cut the pipe to length (remember you can always make it shorter but it's hard to make it longer again) and mark where the ends of the pipe should be on the box.
4. On each end:
   1. Using the outer ring as a template, mark where each bolt hole will go.
   2. Drill out each hole, being careful not to crack the plastic. Use light pressure and low to medium speed, and use pilot holes. The tighter the fitment of the bolt in the hole, the less air will leak through but the harder it will be to get each hole in the right spot. (You can always make the hole bigger, but it's hard to make it smaller again.)
   3. Position the outer ring on the outside of the box and slide a bolt through each hole.
   4. Put the inner ring on the inside, putting the bolts through the holes.
   5. Thread a nut on each bolt to hold everything in place, then tighten the bolts from the outside. Make sure the nuts recess into their pockets in the inner ring. These should be snug but not crazy tight as we don't want to crack the plastic.
5. Put a spool of filament on the PVC pipe and put it in the box, using the inner rings to support the pipe.

Adding pneumatic fittings for PTFE tubes:

1. Position the spool where you want the first spool to sit (remember there will be 4 spools in total and they all need a spot).
2. Pull some filament off the spool and run it to the wall of the box. Be sure the filament is perpendicular to the side of the box so it will slide freely into the PTFE tube.
3. Mark where the filament hits the wall of the box and drill a 6mm hole, being careful not to crack the plastic.
4. Repeat steps 6 through 8 for each spot a spool will go.
5. In each of the four holes, attach an PC4-M6 pneumatic fitting to the outside, secured in place with an M4 nut on the inside. No need for these to be super tight; they won't see a ton of stress.
6. For each pneumatic fitting on the box, cut a section of PTFE tube to run from the box to the printer and press it into the pneumatic fitting on the box.
7. Put some desiccant in the box and throw in a hygrometer if you're a data nerd like me.
8. You can now remove your PVC pipe, mount your spools, and replace the pipe. Feed some filament through each PTFE tube so you can feed filament into the printer without opening the box.

To print from the filament box:

Load the exposed filament at the end of a PTFE tube into the printer like normal and print normally. Unload filament normally. After unwinding, you may wish to open the box and wind the excess filament back on the spool (while leaving a little filament sticking out the PTFE tube so reloading is easy).

3D Printing Tips

I printed all parts in PLA with a 0.6mm nozzle on my stock Ender 3 v2. No parts require supports if printed on the correct face.

Desiccant Management

There are two ways to measure humidity inside your filament box: the first is directly, using a calibrated hygrometer. The other way is to routinely weigh your desiccant, and knowing the dry mass and some silica gel data, approximate the humidity inside the box.

To dry silica gel desiccant, place it in a dry environment for 1-2 hours. Temperature should not exceed about 130 Celsius. A typical atmosphere heated to 100 C should achieve a relative humidity of 1-2%, which is adequate. (If you're curious about this calculation, the search term is “psychrometric chart.”) A toaster oven with the door cracked is a good way to achieve this. Weighing before and after drying gives a good indication of how much moisture was removed.

Pure silica gel is generally considered non-toxic (apart from dust inhalation), but the indicating dyes used (even orange dyes) can have adverse health effects. Some people use a dedicated non-food appliance for drying.

I transitioned from keeping my silica gel loose in the bottom of the bin to keeping it in mesh bags because I've found repeated pouring of the beads created lots of small silica fragments and silica dust which I did not want contaminating my environment. Bags also make the gel easier to handle. Pictures of the loose desiccant remain for posterity.

Potential Problems/Improvements

Keeping desiccant in the bottom of the box: Wet air is less dense than dry air (seems counterintuitive but is true), so it would be better to have the desiccant in the top of the box. However, this would create more problems than I cared to deal with so I used plenty of desiccant in the bottom of the box and hoped that the air would stay reasonably well-mixed.

Changing filament/rewinding spools: Since the Ender 3 uses a Bowden extruder, changing filament requires the unloading of about 50cm of filament, which ends up in a tangled mess around the spool inside the box. This requires one to open the box and rewind the filament onto the spool by rotating the spool by hand. I would have liked to add a way to rotate the spools by hand from the outside of the box so opening the box wouldn't be necessary, but I haven't figured out a good, simple way to do it yet. I mostly just leave the extra filament dangling out the end of the tube.