Show and Tell 3d printable dry boxes

[Andy]

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I recently stumbled on these dry boxes on Thingiverse. They're pretty cool, but they had a couple of problems for me. Namely:

• They use cereal boxes that are ~$15 each, making each box roughly $20. I can get a cheaper bill of materials than that.
• They use some pretty thick parts, making the print time much longer than it needs to be
• Assembly is more complicated than it needs to be
• The filament comes out of the opposite side of the hydrometer

With those in mind, I recreated the concept around cheaper storage bins, and I'm pretty happy with the results so far.

The Bill of Materials​

• 1 Cereal storage container (https://www.amazon.com/gp/product/B087FBCNKN/) ~$5.00 each
  • These are pretty likely to get discontinued (because Amazon), and the project is pretty specifically built for these. If you can’t find them, it’s pretty likely someone else is making the same thing under a different URL. Listed dimensions: 9.6"L x 4.3"W x 9.75"H. Be aware that they have a taper along the sides and inset handles!
• 1 Hygrometer/Thermometer (https://www.amazon.com/gp/product/B08SBNM72Y/), $2.00 each
  • These seem to be a standard dimension, but the dimensions that matter are .813" on the inside diameter, and .15" from back of the "face" to front of the "clips". They don't list that in the linked listing; the listing only say 7.05 x 4.72 x 0.75 inches
• 2 or 4 Ball Bearings, depending on which version you're building (https://www.amazon.com/gp/product/B07216D1SZ/) ~$0.50 each
  • These appear to be standard dimensions, but are listed as 0.31 x 0.28 x 0.87 inches
• An amount of silica gel beads (https://www.amazon.com/gp/product/B013L31PQ0/)
  • These are listed as "industry standard 3-5 mm", but any bulk beads would work. These are nice because they change color when they get saturated
• ~2” of PTFE tubing

The Printed Parts​

All of these parts should be able to print as-is, with no supports or bed adhesion needed. Some of the taller/smaller parts might benefit from a brim to prevent them from pulling from the bed, but it’s not super required. All of the parts can be printed with your go-to settings (for me it’s 3 walls and 20% infill).

Note that the feet and filament tube end cap are optional. The feet will give a nice space for the base, with a good amount of room for the silica beads, but I’ve found that you can just put the base directly on top of the beads. All that the filament end cap does is protect the last ½” of filament.

For the 1-roller variant​

• Print 1 base (estimated 44g/7 hours)
• Print 1 peg and end cap (estimated 3g/45 minutes)
• Print 1 roller (estimated 9g/75 minutes)
• Print the filament tube, gasket, and (optionally) an end cap
• Print 6 feet (optional)

For the 2-roller variant​

• Print 1 base (estimated 25g/4 hours)
• Print 2 pegs (estimated 5g/90 minutes)
• Print 2 rollers (estimated 17g/2 hours)
• Print the filament tube, gasket, and (optionally) an end cap
• Print 6 feet (optional)

Assemble​

1. Assemble the rollers
   • Press-fit the bearings into the ends of the roller(s)
   • For the one-roller variant: slide the peg through the roller and super glue the end cap in place (be careful not to get glue on the bearing!)
   • For the 2-roller variant: slide the pegs through the holes in the base and through the rollers
2. Mount the filament tube
   • Mark where you’re going to drill the hole in the bin. I found it’s best to actually dry-fit the beads+base into the bin and then roughly eyeball it
   • Drill a 5/16” hole at your mark, super glue the tube in place, and then super glue the gasket in place on the front of the bin.
   • Cut a length of PTFE tubing and glue it in place. You could cut it exactly to the length of the tube (and that’s what you should do if you’re using the end cap), but I like to leave an inch or two sticking out the end to guide the filament, so that the box doesn’t need to be pointing directly at the printer.
3. Mount the hydrometer
   • Take the back off of the hydrometer with a small screwdriver (there are 2 small tabs that pop out).
   • Slide the hydrometer in place
   • Pop the back back in place
   • You might want to take the LCD out as part of this. If you do, make sure you mark which direction is up, because if you install the LCD upside down, you won’t know it until you’ve put the whole thing back together.
4. Bring it all together
   • If you’re using the feet, glue them in place and put the base into the bin
   • Pour a small amount of silica beads in the bin (1-2 beads deep is plenty)
   • If you’re not using the feet, put the base in now
   • Run your filament through the hole in the front of the base and out through the bin
   • Either set your filament on the rollers or place the roller inside your filament and guide the roller onto the base.

​

The 1-roller and 2-roller variants. The 2-roller version is slightly faster to print, but the 1-roller version uses slightly less filament and handles a wider variety of rolls (cardboard rolls tend to not be perfectly manufactured and will "rock" back and forth on the 2-roller version).

Next steps, improvements​

Like any project, these have plenty of room for improvement, and actually making those improvements is on my todo list, but lower than *points vaguely at everything*. Some of the issues I've come across so far:

• I'm finding out that some spools are juuuust so slightly wider, making them not work with the 2-roller variant. I'm also skeptical that the 1-roller variant isn't too tall for some spools, which would make them hit the "ceiling" of the box.
• I haven't been able to figure out a good way to get filament back in to the box once it's been pulled out--I usually take the lid off and roll them back in, which defeats the purpose of a dry box when your ambient air is 60% humidity on a dry day. Perhaps it's possible to have the filament tube come out through the top, making it easier to feed back into the box, or perhaps there's a way to put a winding key that goes through the side (which may eliminate the need for an internal base altogether).
• Putting the hydrometers in place is annoying at best. It's not super hard to disassemble/reassemble, but these hydrometers have "clips" that stick out but don't actually push in like a clip would (meaning that a hole would have to be cut out for them, and the whole hydrometer would be loose in the stand). Perhaps a different style would work better?
• I'd like to make a "card" holder on the front of them that can hold a sample print card for the filament that's inside the box.

These still need a bit more testing. I may post the STLs here or on Thingiverse once I have them a bit more refined, but these may also work better as a starting point for your own ideas! What else would you improve on these?

 

[Andy]

So these worked OK for a while, but two problems popped up:

1. they only rolled ok at best. There was kind of a lot of drag that I couldn't figure out. I suspect it was the ball bearings or my roller <> stand tolerances were too tight
2. I bought some filament that came in a cardboard spool. These are fantastic, except that they don't have the absolute precision of injection-molded parts, so they would "wobble" on the rollers and hit the sides of the box. You can see me starting to troubleshoot this in my last post, but I never really solved it.

I tested a couple of other options that would keep the box self-contained, but finally I just gave up and ran a "peg" through the side of the box. While I was doing that, I also ditched the hygrometer. It's a nice data point, but it's basically redundant--either the desiccant beads are working or they're not. If you get color changing desiccant, then just look at that and replace them when it changes color. I also just made the tolerances for everything looser, meaning that parts can slide over each other without bearings.

The final version has 6 parts:

• A flange that you glue to the outside of the box (over a hole that you drill)
• A flange that you glue to the inside of the box (opposite of the hole you just drilled)
• A peg that runs between the two flanges
• A roller that sits on the peg, inside of the filament spool
• A filament feeder tube that goes through a hole in the front of the box, and a gasket that you glue onto it

The outer flange has an inset "catch", and the peg has two small feet that catch into it. The far/inner flange then has a drafted hole that matches a flare on the peg. Between those two elements, I haven't had a peg come loose.

The total cost for each box, including filament, electricity, and parts is just over $5, and the printed parts take just over 4 hours.

I'll take it!