I bought some bearings off of eBay without really checking what others use. Later i didn't find a pump that uses my bearings so i made one ... I also was a bit disappointed that nobody released step or fusion files for their pump so i did that too.

by default:

• it uses 626 (6x19x6 mm) Bearings
• it uses 6-OD 4-ID mm Tube -> ~5,5mm OD -> ~1mm wall thickness
• it uses a m3 nut and screw to lock the rotor onto the D-Shaft of the Stepper.
  • when pressing on the shaft it makes sense to slightly warm it to help push away bits of plastic, especially at the screw hole. i sadly found, that having that loose enough for an easy fit makes it to unprecise. proof me wrong and do it better xD pls.

i tried to make the File simple to Customize ... and i failed successfully with that. Im not a professional Designer but the important bits are easily Customizable.

if you happened to have the same (6x19x6 mm) bearings, then i found that the 14.00 size rotor is the best with my printer. I was surprised to find, that minimal changes make a lot of differences. The main problem is, when its to tight, then the Stepper just looses steps or the rotor breaks if you force it. If too lose then you get bad flow and the liquid will flow back.

Check my other Designs, i think I'm not yet completely done with this thing.

With the 14.00 rotor, i found that the backflow (with water in the tube <- its different with air) is close to 0 on 2 of the 3 sides of the rotor (unprecise stepper hole and all that) and its working reliable.

if you just wanna change the tightness of the Rotor:
Go in Fusion, and go for the 3rd 2D Sketch in the Timeline, the Distance from the "bearing" to the middle is what sets the Pressure for the tube, by double clicking it, you can change it and it will affect other things in the Part, too. Again it seems that even 0.02 mm make a significant difference (its the Radius so its affecting double but still surprisingly sensitive) so start small and see what it does. Luckily the rotor is literally a 8 minute part so its easy to just trail and error.

have fun with the files :)

Also ignore the Typo... xD