Improved Spool Holder for Anycubic Kobra S1 3D Printer

My spool handling system for all my FDM printers consists of a 30mm diameter tube that attaches to each of my printers, and a spool adapter kit that fits that tube.

While my Anycubic Kobra S1 was purchased as a bundle including the ACE Pro filament handling system, I do print quite a bit of TPU lately which cannot be fed through the the ACE Pro unit.  As with every FDM printer I own, the stock filament holder does not provide for smooth motion and easy de-spooling.  I adapted the tube mount I made for my TwoTrees SK1 so that it would fit the Kobra S1 and allow me to use my spool adapters that ensure smooth and easy filament feeding.

I've included the tube and nut so this can also function as a basic spool holder, but I STRONGLY recommend trying the spool adapters with this because the whole point in this and my other similar designs is to have the filament de-spool easily without the excessive drag of a spool flopping around on a hanger.

My spool adapter kit is at:  https://www.printables.com/model/515029-improved-universal-spool-adapter-for-fdm-printers

The mounting bracket of this model attaches to the Anycubic Kobra S1 in the same place the little stock spool holder attaches, using the same screws.  Mounting the spool on the back side of the printer is not a design choice I'd have made, and there are designs out there that relocate the spool holder to the right side of the machine.  Currently, my ACE Pro unit resides alongside my Kobra S1, so relocating the spool mount to the right side, which would be preferred by most, will not work with my setup, which is why this model mounts in the stock location.  I did place the ACE Pro atop the S1 so I could rotate the machine to install this and photograph it, so pay no attention to the routing of the PTFE tubes in those photos.

The bracket portion prints easily as oriented in the STL but will require supports to “buildplate only”, which are easily removed.  The tube and nut print easily as oriented in the STL's without supports, however, the tube portion may benefit by the use of a brim if the machine it's printed on doesn't have good bed adhesion.

I printed this in Kingroon blue PETG because that's what I happened to have loaded but should work fine in whatever rigid material you choose.

NOTE:  The tube portion of this model is 30mm longer than the stock steel hanger and it's base adds another 4mm to the total depth of this spool holder.  The added depth of this design amounts to 34mm, and is necessary for accommodating all the spool types I'm using along with spool adapter for smooth rolling.

UPDATE 06262025:  So that I don't have to constantly undo the PTFE tube from the extruder to the filament sensor to use the external spool holder on my S1, I added zpin's 5-to-1 Filament Hub for Anycubic Kobra S1 Combo to the mix.  I've not been able to fully test zpin's hub since my TPU is saturated, but I think it's going to work great for swapping from the ACE Pro unit to the stand-alone spool.  Zpin's model is available at:  https://www.printables.com/model/1291687-5-to-1-filament-hub-for-anycubic-kobra-s1-combo

UPDATE 07032025:  Having been installed for a week, and after many TPU prints, I've found that Zpin's 5-to-1 filament hub to be a fantastic solution for effortless swaps between using the ACE Pro and the S1's backside spool holder.  For those experiencing under-extrusion with TPU on the S1, Zpin has another design that bypasses the filament detection switch by relocating the switch and adding a two way splitter above the switch.  Zpin's “Kobra S1 Optimized Filament Sensor Relocator Bracket with Rotatable Y-Joiner” is available at:  https://www.printables.com/model/1312519-kobra-s1-optimized-filament-sensor-relocator-brack

UPDATE 07062025:  After having this model off of my Kobra S1 for a few days for some experiments, I decided to beef up the base of the “KobraS1_Spool_Tube_Bracket.stl”  to increase the surface contact with the holder opening at the back of the machine.  That depression for the spool mount on the back side of the Kobra S1 was a little deeper than my original part measured, so I added .5mm to the brackets depth.  When I modeled that part initially, I used measurements from the stock holder which were unnecessarily smaller than its mounting position.  While I had no issues with version 1 of this design while it was mounted, I think the V2 file is a better and more solid fit to the machine.  The added file “KobraS1_Spool_Tube_Bracket_V2.stl” is the part I'm currently using on my Kobra S1.

UPDATE 08052025:  The mounting bracket for the spool tube will mount on the Kobra S1 so that the spool will be either shifted right or left.  When I installed that bracket on my Kobra S1 initially, I did so with the spool shifted to the left, allowing for better clearance between the spool and filament hub.  Having recently installed another of zpin's models, “Anycubic Kobra S1 Left-Side Steep Poop Chute with Bin”, I flipped the bracket around to provide clearance between the chute and rear hung spool.  It turns out that mounting the bracket with the spool tube shifted right does NOT interfere, with even the upgraded spool hub “also of zpin's design” which is larger than the stock four port hub since the shoulder of the spool tube prevents spools from touching the hub.  Install the bracket whichever way suits your particular setup, but having the spool tube shifted right is probably the best orientation for most.  Zpin's “Anycubic Kobra S1 Left-Side Steep Poop Chute with Bin” is available at:  https://www.printables.com/model/1291774-anycubic-kobra-s1-left-side-steep-poop-chute-with

While neither of Zpin's solutions add additional friction to the filament path, the filament detection bypass solution removes the friction induced by the filament detection switch itself.  I prefer Zpin's 5-to-1 solution as it maintains filament detection for the backside spool.  The backside spool holder is a pretty bad idea to begin with due to cumbersome filament changes, and since it's out of sight, it would be really easy to start a print without realizing there's not enough filament to complete the print.  For me, Zpin's 5-to-1 hub solution is the better fix, but your mileage may vary.