Kobra 3 Combo | 9 Position Bowden Tube Hub UPDATED
## 9-in-1 Kobra 3 Multicolor Hub v1 V2.1
I made this because the hub linked by Anycubic in its recent 8-color announcement email was a bit crap, didn't function like the original, and everyone else seems to have forgotten about the 9th bowden tube for the freestanding roll option. You know, the one that you'll need to use if you want to print flexible filaments. I printed the hub upside down with supports on the flat areas. Other parts are printed with the largest flat area on the build plate. I do recommend using a skirt to avoid warping.
V2.1: Fixed the medium top plate and spring raft that were too big. 11/16/2024: Reuploaded the Large Top Plate and Large Hub Body STEP files because the existing files were corrupted.
V2 UPDATES:
The spring caps, spring raft, and the cap have all been edited for better printing and for better clearances. The angle of the funnel inside the hub has been edited for smoother feeding. The spring raft has been edited to direct the filament into the body more easily. Some other clearances have been tweaked. I've also removed the STL files in favor of STEP files, which seem to work better in the Anycubic NEXT slicer. I've uploaded both STEP and STL files for your convenience. Furthermore, I've added another size option, explained below.
This part should allow you to leave all of the bowden tubes hooked up all of the time, which means you'll only have to turn off the ACE Pro to switch to "normal" printing with a single spool.
The "Small" files are sized for the parts harvested from the hubs that comes with the Kobra 3 or parts of the same size. The wall thickness is quite thin, and I may update this to make it a bit stiffer.
The "Large" files are a larger version that is sized to work with the parts I was able to find cheaply on Amazon with Prime shipping. The collets have a larger top diameter and the springs are a bit longer. This version fits, but applies a little bit of pressure to the print head module cable. That led to the medium size below.
The "Medium" files are a trimmed-down version of the "Large" version, making the hub a little smaller. It is still designed to be used with the aftermarket parts: the larger diameter bowden tube collets and the slightly longer springs.
### Additional Parts Required
1. *Springs:* You can cannibalize a few stock hubs and get the springs that way. They're 12mm long by 7mm OD by 0.4mm wire diameter. I ordered some 15mm x 7mm x 0.4mm springs from Amazon and they work just fine. I haven't found a source for the 12mm long ones.
Affiliate link: https://amzn.to/3NfVjQA
2. *Bowden Tube Clamp/Collet and Clip:* Again, tear down some other equipment for parts, or you can buy these:
Original Size @ AliExpress https://www.aliexpress.us/item/3256807454831680.html
Larger Size @ Amazon Affiliate link: https://amzn.to/3Y9ukg2
### Other Notes
I've designed the top to fit a couple of different ways. ~~First, I designed little clips like the original injection-molded part. I have found that PLA tabs just like to break off when being used more than once, however. If you put it all together and don't ever disassemble it, it should work fine. However, if you need to pull it apart and break the clips, you can use the cap, which slides over the top and locks into the same slots. It is installed in the pictures.~~
As I use this, I may make some additional changes to improve usability or performance. PLA should be fine as a material, but PETG seems a little slicker. If you're worried about friction, maybe try that. Give me some feedback!
This part was designed with Fusion360 after measuring the original hub with a cheap set of digital calipers.
