Permanent Desiccant Container

Update: 

Added versions with side holes, and an updated OpenSCAD file to produce them. The 25x25 version now has two grate support beams, and there are also 40x40 and 50x70 versions.

I also attempted microwaving two of the cylinders I printed in colorFabb allPHA. They both measured 90-95C and were squeezable (normally hard), and a layer broke from the squeezing. Some of the beads had stuck to the inside. The temperature inside may have been much hotter to cause this (the heat deflection temp is claimed 120C). I also think the steam was condensation inside the container, preventing more from evaporating.
So, if you try microwaving these, go slowly. I had much better results using my typical food-dehydrator-as-filament-dryer at 65C over 16 hours, they had a much lower weight after compared to microwaving. I may end up making a forced-air heater after all.

Original Description:

This is a desiccant container that doesn't come apart: you print it, the print pauses for you to fill it up, then it finishes printing.

The idea is that you use a filament that doesn't melt at whatever temperature you plan on drying the desiccant at, and just dry it in the container. I used allPHA from colorFabb, which they claim is both easily biodegradable (unlike PLA), and has a heat deflection temperature of 120C.

The container is 25mm x 25mm x 25mm, and can hold roughly 5g of 2-4mm silica gel beads. That would be equal to 1g of water absorption capacity at ambient conditions (own tests for silica gel resulted in 21% and 23% weight increase, so assuming 20% is a good estimate for ambient). It's not enough to dry out a spool on its own, but can be thrown in the centre hole of any spool that's just been dried and should keep it dry for a while.

We use infill with no solid top/bottom layers to achieve a fine grate. There's a “foot” and beams that help supporting this infill: this was necessary because the grate will tear apart quite easily when stuck solidly to the bed. It also hides the ugly infill edge and protects it from damage.

Downside of this model is that if your filament isn't clear, you have trouble seeing any indicating beads even if you hold it up to light. One option is drying the finished part and then weighing it, then leave it out for a couple of weeks and weigh again to get the range. This is good if you are concerned about the possible negative health effects of the indicating dye and perhaps want to use this to keep spices/etc dry.

Some printing notes:

• I've not provided g-code, because all I have is a modified Prusa Mini and so can't confirm any g-code will be good on any stock printer.
  • Use the settings you usually use and confirm the steps I've put in the image. The .3mf file has the necessary settings and you should be able to just set the presets you want, but make sure you confirm they're still all as they should be.
  • I printed with a 0.4mm nozzle and 0.2mm layer height, the settings probably have to change if you're using different. E.g. the infill % may need to change to get the holes at a good size to not let bead fragments out.
  • You can place a cube in PrusaSlicer to get an idea for how fine the grate holes are.
  • You can rotate the print and the fill angle setting on the container to help get the infill bridging supported as well as possible.
  • If you can't get both bottom and top grates supported well due to resizing or changing layer height:
    • The bottom infill bridge is way more important, because you'll actually have to look at that bridge.
    • You can rotate one end only in PrusaSlicer (mine's 2.8.0) by cutting it in half vertically.
      • Do not let it fix the model, it will break.
• I've provided the OpenSCAD script, but I can't promise it'll work with any parameters you enter or that I've made no oversights. Confirm everything's as it needs to be before printing.
• This definitely warped with allPHA using PVA bed glue. The glue that worked is a discontinued Pritt Stick Xtra Strong, but I think it is PVP-based.
• Don't fill the container to the brim with beads, the filament will probably stick to it and start dragging it around.
• PrusaSlicer reports errors, but fixing them breaks the model. Not sure why this is a thing, I only used basic cylinders and difference operations in OpenSCAD to produce the model, apart from a polygon which doesn't fix the errors when removed.
• Your chosen filament needs to survive the temperature you want to dry at.
  • If you're planning on printing with PLA or other low-temp filament, keep in mind that it might be hard to get sufficient airflow into the container for low-temp drying to be effective. You could try making a forced-air dryer (like a radial fan mounted to a 25mm circular hole, place it in a food dryer), but this isn't really designed with that in mind.
• The wetter your filament is, the more it'll ooze during the pause. This might translate into slightly less material at the location where it restarts printing.