Honeycomb Tube Rack

This is a special 50 mL Tube Rack. It is able to store up to 9 tubes at once and it was designed with compact storage in mind. Ideal for storage of samples in small fridges and tight spaces. For this design, my goal was to make it as compact and cheap as I can make it. I started with a basic honeycomb pattern in Fusion 360. I took inspiration from various tube racks in the lab and different designs on Thingiverse. I tried different kinds of feet for the bottom part, but these bigger more rigid ones came out as most reliable. Depending on your region each rack should cost you less than 5 € easily, which is far cheaper than I was able to get one in stores.

Update V2  2023-06-15

Added new version where M3 nuts can be embedded into the part due to feedback from Nick Glennon. This reduced the number of nuts needed in half so only 12 are needed for 1 tube rack. I used dimension and tolerances from Prusa i3 MK3S+ Printable parts which works really well. Using glue to hold them in place is highly recommended however so nothing falls apart during use. Assembly in this version gets a little bit more tricky with this version compared to the original because it is hard to keep the whole layer horizontal.

Update V3  2023-06-15

Similar to V2 this version also only needs 12 nuts however to ensure nuts don't fall out there are slots for them the slide in from the side. Again, Prusa i3 MK3S+ Printable parts dimensions and tolerances are used. To make it easier to print a sacrificially support layer is used. Please use a knife to remove the material where the rod is intended to go! 

Positive aspect about this design is that there is no glue needed, however assembly seems even more difficult compared to V2. Also, V3 seems to be least stable and doesn't feel as rigid compared to V1 and V2.

Ideas for future Versions   feel free to remix ;-) 

.) Heat set inserts - may add stiffness and are also very cost effective and fast to 

.) 3D printed rods - horizontally printed rods may be rigid enough to make the whole design 3D printable.

Advantages over conventional tube racks

.) Less material use

.) Light weight

.) Compact design

.) Fast & easy print

.) Low cost

.) Drainage holes for accidental leaks

.) Easy to read tube labels from side and top view

Additional features

.) Suitable for freezing

.) Water resistant

.) Chemical resistance (if printed in PETG)

.) Colour coding depending on filament

Final thoughts

I am very happy how this design turned out. We use them in the lab for half a year now and hadn’t had any issues with them, even at cool temperatures. PETG is an ideal material for lab use due to its chemical resistance and no moisture absorption, but it isn’t autoclavable unfortunately. Printing the design in PC (no resistance against acetone), PEI or even PEEK can solve this issue, but these materials aren’t suitable for many printers. Also, I am thinking about how the assembly time can be further improved. Right now, it takes me about 10 to 15 minutes for each tube rack. I thought about 3D printing the rods as well, but I didn’t get good results with this technique. Regarding different 50 mL tube designs, I can tell you that I have tested 50 mL tubes with built in stand and they work as well.

Enjoy.

Print instructions

Materials needed for one Honeycomb Tube Rack

.) 4x 86 mm long M3 threaded steel rods (3 mm diameter)
.) 24x M3 nuts (3 mm inner diameter)
.) Optional: 24 M3 washers

Print parameters

Each tube rack is made out of 1 bottom part and 2 top parts. I printed them on my modded direct-drive CR-10 with a 0.8 mm volcano nozzle and 0.4 mm layer heights. You can probably use your normal slicer settings, I just wanted to cut down on print time as much as possible. No brim needed, 100% infill.

Assembly instructions

Cut the M3 threaded rod into 86 mm long pieces. You need 4 for one Tube Rack. File sharp edges. Once all parts are printed and cleaned you can start by inserting a nut on each rod. Insert the bottom plate and secure it with another set of 4 nuts. I used two wrenches to tighten both nuts. Add another set of nuts onto the rods in about 45 mm distance to the bottom part. Add one top part and work your way up until the rack is finished. There should be around 27 mm distance between the two top parts.

You can vary the length of the rods and the space between the pieces depending on your needs. Feel free to try out which one works best for you. If you think your 50 mL tubes aren’t sliding in well enough you can try adding a fourth layer. You can also use washers if you experience any loose nuts over time, but in my experience this wasn’t necessary.