Filament Drybox for 8 to 10 spools

Background and idea

When printing TPU or PETG, the results will be much better, if the filament is dry. In my experience, the filament should be stored at about 20% relative humidity (at least below 30%). I wanted to print directly from the dry box hanging on the wall above my printer. The filament should run very smoothly and with minimal friction, so that there is minimal additional load on the extruder's stepper motor. A single spool should be easily replaceable without removing other parts. The desiccant should be easy to remove for regeneration in an oven.

I found a solution in a smartstore classic 31 box. Two rows of four 1 kg spools or five smaller 750 g spools just fit in this box. Each spool is supported on four ball bearing rollers and the filament is fed out in teflon tubing.

This build is not a simple one. Read all the instructions carefully before you begin.

What you need to buy

• 1 piece smartstore classic 31 box –> local DIY store (around 15 €, less if you get 3 pieces)
• 4 pieces of aluminium rods ø 6mm x 305mm –> local DIY store ( Attention: the rods vary in diameter from 5.8 to 6.2mm -> take a caliper gauge with you and try to get rods with a diameter between 5.95 and 6.00mm )
• 2 pieces of aluminium rods ø 4mm x 305mm - these two rods are optional, they give a little more stability –> local DIY store ( Attention: the rods vary in diameter from 3.8 to 4.2mm -> take a caliper gauge with you and try to get rods with a diameter between 3.95 and 4.00mm )
• 32 to 40 pieces of ball bearings 608 (22mm x 8mm x 7mm) as used in skateboards –> local DIY store or order at aliexpress ( get some with low friction )
• 10 pieces PTFE tube ø inside 2mm x ø outside 4mm x 30mm –> order at aliexpress
• 11 pieces cylinder head screw ø3.5mm x 19mm with thread for chipboard –> local DIY store
• 2 pieces of wire mesh nets 500mm x 320mm to hold the desiccant bags for easy removel
• 12 to 30 pieces of desiccant bags as used for filament spools or similar –> aliexpress or recycle from filament spools

Optional, but highly recommended, because you need to know, when to regenerate the desiccant:

• 1 piece hygrometer –> aliexpress https://www.aliexpress.com/item/1005005397633283.html - I chosed version T, because it works with Apple Home Kit and Thread ( Attention: if you prefer another hygrometer, it must be maximum 14mm thick, otherwise it will touch the spools )

What you need to print

• 32-40 pieces of rolls ( printed in TPU )
• 32-40 pieces of bearing supports ( Attention: read „How to Build“ first for the correct dimensions ) 
• 2 pieces of axle support left
• 2 pieces of axle support right
• 1 piece outlet top
• 1 piece outlet bottom
• 1 piece outlet gasket ( printed in TPU )
• 1 piece hygrometer support, if you choose the same hygrometer
• 6 pieces of lid clips –> https://www.printables.com/model/608613-lid-clip-for-smartstore-box-classic-31
• If you want to hang the dry box on the wall, use 2 pieces of wall hooks –> https://www.printables.com/model/608690-wall-hook-for-smartstore-box-classic-31

Printing recommendations for the rollers and the gasket ( printed in TPU )

I choosed TPU for the rollers so that the spools do not slip and run very quietly. The surface of the rollers where the spool touches, should be as smooth as possible to reduce friction. For this your TPU filament must be very dry and some slicer settings are important (see below and see the .3mf file)

• TPU (soft TPU recommended) – I used Extrudr Flex Semisoft clear.
• Nozzle diameter 0.6mm – I used 0.6mm BondTech CHT nozzle.
• Layer hight 0.3mm
• Perimeters 22 – the perimeters should fill up the whole roll / gasket
• No infill
• No supports
• Set „Avoid crossing perimeters“ – less stringing with TPU
• Set „Seam position“ to „Nearest“ – for a smooth rolling surface
• Set „Staggered inner seams“ – for a smooth rolling surface
• Set „Max volumetric speed“ to 5mm3/s or even less – TPU has to be printed slowly
• Set „Complete individual objects“ – to print each roll individually

Printing recommendations for the bearing supports

This is where it gets a little tricky, because you need to select (and try) the correct dimensions for your aluminum rods and bearings. Your printer may have a different precision than mine. Let's say your bearings have an exact inner diameter of 8 mm and your aluminum rods have an exact outer diameter of 6 mm. Then first print a bearing support with 8.2-6.2 mm. Insert it into the bearing. It should go in with little force but it should not fall out by itself. Then insert the aluminum rod into the bearing support. It should be easy to insert, but should more or less stay on the rod (not move around by itself) and be able to be moved sideways with little force to adjust the rollers to the width of your filament spools. If the printed bearing support does not meet the criteria, print another with better fitting dimensions until the criteria are perfectly met. You may have to try several times until you find the right dimensions. Then print the 32 to 40 pieces you need.

• PETG or similar. – I used Prusament PETG Clear.
• Nozzle diameter 0.4mm
• Layer hight 0.2mm
• Perimeters 10 – the perimeters should fill up the whole bearing support
• No infill
• No supports

Printing recommendations for all other parts

The Axle Supports have two round brims at the ends to avoid warping. Cut them off with a knife after printing.

• PETG or similar. – I used Prusament PETG Clear, because it fits perfect with the color of the box and the aluminium.
• Nozzle diameter 0.6mm (or 0.4mm) – I used 0.6mm BondTech CHT nozzle.
• Layer hight 0.3mm (or less)
• Perimeters 3 (more with thinner nozzles) – for stability reasons (for the outlets top and bottom 2 perimeters are enough)
• Solid layers top 4 bottom 3
• Infill 15% cubic
• No supports

How to assemble the filament spool carrier

• Assemble the bearing supports, the bearings and the rollers.

• Position them on the 6mm aluminium rods according your filament spools (75mm for 4 Spools or 60mm for 5 spools).

• Place the axle support on both axles at the same time and add the two outer rollers.

• Insert the 4mm aluminium rods into the axle supports at the same time.

• Check with a filament spool, if the width is correct and it turns smoothly.

How to build the outlets into the box

• Insert the spool carrier into the SmartStore box.
• Use the the top outlet as a guide for the holes in the SmartStore box.
• Position the top outlet as shown in the picture.
• Mark the two outer holes with 4mm wood drill bit or similar, use some waste wood underneath the box and don’t press too hard, the box may crack.

• Remove the spool carrier.
• Mark the other two outer holes with the help of the top outlet as a guide.

• Drill the four corner holes with a 10.5 or 11mm wood drill bit or step drill bit, but don’t press too hard, the box may crack.

• Mark the outer dimensions of the complete rectangular hole

• Saw out the rectangular hole (leaving round corners from the drill bit) with a saw or a dremel or vibrating saw or similar, but don’t press too hard, the box may crack.

• Check that the bottom outlet fits into the hole.

• Put the gasket and the top outlet on top.
• Check if everything fits and is well sealed.
• Put the eleven screws in place, but do not tighten them fully down jet

• Insert the ten teflon tubes
• and now tighten the screws fully.

• Insert the the spool carrier with the teflon tubes in the center.

• Check that everything is running smoothly

• Position the hygrometer with its support in the center next to the lid and check that the lid still fit on it.
• Clean the inside of the box where the sticky tape will go with isopropyl alcohol or similar, otherwise the hygrometer will fall off within a few weeks.
• Stick the hygrometer support in place with double sided clear tape.

• Fill the box with filament spools.

• Close the box with the lid clips.

How to build the desiccant holder

• The following mesh folds are easily done by clamping the mesh net to the edge of a table and using a spatula or similar to fold the net over.

• Fold the wire mesh net 10mm inward on both long sides so that the final width is 300mm –> These edge foldings are there to protect against injury.

• Fold the mesh net 100mm inward on both short sides (to the same side as before). The final length does not matter.

• Fold the mesh net in half, with all edges folded inward. The size will be 300mm by around 240mm.

• Mark 3 or 4 vertical lines equally spaced ( 4 spools –> 75mm or 5 spools –> 60mm ).
• Mark a horizontal line 220mm from the long side where the fold is. The mesh net will be bent along this line later to get handle.

• Fill the mesh net with desiccant bags between the marked lines. The bags may overlap to fit within the 220mm line.
• Now you can join the two sides of the mesh net in two different ways:
• 1. The beautiful way: use metal threads ( i.e. from the mesh net ) and sew the two side along the marked lines together.
• 2. The quick and easy way: use staples to hold the two side together.

• Bend the mesh net at the 220mm line to shorten the desiccant holder and make a small handle.

• Finely place the desiccant holder into the smartstore box on the short side with the handle facing the center of the box.

All done. Happy printing.

How to use the dry box and regenerate desiccant

Try to keep the box closed as long as possible. If you have to open it, i.e. to replace a filament spool, do it as quick as possible.

After inserting filament spools and desiccant for the first time, it will take around two or three days until the moisture of the air inside and of the filament finds an equilibrium and a minimum. After that it will start to slowly rise again, because your (probably not so dry) filament spools will transfer moisture to the air and to the desiccant. After two to four weeks or if the moisture rises above 25% rel. humidity, remove the desiccant holders from the box, put it in an oven for 1 hour at 100-120°C with circulation air. That regenerates the desiccant. When you put the desiccant holder back into the box, watch out not to melt the plastic box with a too hot wire mesh net. Now it will take one or two days to reach a minimum at around 10 to 20% rel. humidity. When the humidity rises above 25% again, it’s time to regenerate the desiccant again. Of course when you open the box, the humidity will temprarely rise above 25% – no problem as long as it falls below 25% with a day after closing the box.

The more you open the box the faster the humidity reaches 25%. I have to regenerate the desiccant every two to four month and after regeneration the humidity falls down to 10% or even lower.