Spool-hole Dessicant Canister

Lots of people have designed containers for desiccant (silica gel). Lots of people have designed such containers to fit in the centre hole of a filament spool.  This one is mine.

Features

• Sized to fit in the 50mm centre hole of standard 1kg filament spools.
• Hexagonal shape allows airflow at the sides of the canister.
• Shorter printing time (3 hours) than other designs.
• Threaded cap
• Wings on cap hold canister at the top of a stack of spools.
• Fusion 360 archive provided for easy remixing.

I designed it to use with my cheesy dry-box solution: 19L plastic buckets from Home Depot. They have an airtight lid, and can hold four 1kg spools stacked up, plus some smaller spools tucked alongside. I used to just toss in the desiccant packs that came with new spools, but they're small, and I think they're all depleted. I found the humidity in my buckets was scarcely less than the room.

After filling the canister with freshly-baked silica gel, the relative humidity in my dry buckets dropped from 50% to 38% overnight.

After Printing

Just a little bit of sanding the top of the canister neck, until the cap can screw on enough to align with the canister.

Design Rationale

Other similar canisters I found were typically round, which leaves no space for airflow at the sides.  And they typically had either vertical slots on the sides, or a pattern of small holes. Small round holes are liable to get blocked by a bead of silica gel. And either way, the print time is long, as the printer pecks away at a multitude of tiny features.

According to PrusaSlicer for my Prusa i3 MK3S+ with standard “0.20mm QUALITY” print settings, those other models have print times of 4.5 to 6.5 hours.

I made the slots horizontal. The printer can form the slots much faster, by just bridging across them. (This is another reason why it has to be polygonal, rather than circular: it's much harder to print a curved bridge.) As a result, my model prints in 3 hours.

I put wings on the cap, to prevent the canister from dropping all the way into the spool. This way, the canister can be kept at the top of the stack of filament spools. It's somewhat counter-intuitive, but humid air is actually less dense than dry air (an H2O molecule weighs less than an O2 or N2 molecule) . So, you want the desiccant at the top, where the most humid air is, to be most effective.