Filament Dry Box with hygrometer

This design allows you to convert an off-the-shelf cereal box into a dry box for your filament, equipped with a hygrometer, removable jar of silica gel and a bowden-coupled output port. 

The box is hermetic and will maintain anywhere between 17-25% RH inside for a secure long-term filament storage. It is a very safe, passive solution posing no fire hazard, unlike popular heater-based dryers. 

Materials list:

• (1x) 4l plastic box for cereal (see pictures) 
• (1x) pneumatic coupler for PTFE tube (I've used M6-threaded version and directly screwed it into the lid)
• (1x) hygrometer (a popular, white module with LCD display showing humidity, temperature and a sad/happy face, size: 43x43x13 mm, powered with a CR2032 battery) 
• (4x) ball bearings, dimensions: external 16 mm, internal 8 mm, width 5 mm 
• (3x) M3x6 mm screw 
• silica gel 

If you want to connect the box to your printer remember to buy and additional coupler and some PTFE tube. For this purpose I recommend a tube with internal diameter 3 mm, which gives less friction than more popular, tighter tubes. 

Assembly is very straightforward and shouldn't take longer than 5 minutes. Be extra careful when sliding the rollers with bearings into their places in the base. It's quite easy to snap their holders from the base at this point. 

Editable CAD models are attached to allow for customization and remixes :) 

Known problems with this design: 

• silica gel box lid is difficult to print and requires you to get creative with supports  
• the base element has 2 weak points and is easy to damage before connecting to the bottom bracket (for example while removing from the build plate… ), at which point it gets enough reinforcement to handle normal use