Precision Single Bearing Spool Rollers

Update July 15th 2025:

• No cutting threads with screws anymore. Fastening via M3 nut in left axle.
• Made bearing axle part slightly shorter, for more squeeze
• I provide the STEP files as well (I found the to be more accurately sliced in Orca)
  You find them on a plat in the slicer file.
   

The main goal was to achieve as much stiffness as possible so there is no play between the axle and the 608 bearing.

In order to achieve this we need a high precision fit.
That's why there is Clearance Test models you can print first to prevent wasting material.

Hardware you'll need:

• 608 bearings (1 per spool roller). 22x7mm with 8mm hole.
• M3 20mm screw with cylindrical hex head
• M3 nut
• Hex key

Print Clearance Test

Make sure your printer is properly calibrated (xyz dimensions).
This model is intended for 0.4mm nozzles but I also was able to print it with an 0.6mm nozzle no problem. Layer height: 0.2mm.

Note: In OrcaSlicer you can play with X-Y-hole and X-Y-contour compensation as well to tune the fit.

Print the Clearence Tests (A, B, C).

Then fit the bearing into the hole and unto the axle peg (see image). The tighter the fit, the better!
The Hole gives you the fit for the Housing. The peg gives you the fit for the Axle.
Make a note of the best fitting version (A, B or C).
It could very well be that the outer diameter of the bearing fits best with C (Bearing Housing) and the inner diameter (Axle) with B.

Choose the appropriate version of the Bearing Housing and Axle stl files to print.
Maybe put them in a folder for later use.

Print the Spool Rollers!

Note: I provided a .3mf slicer file. I used OrcaSlicer. I added modifiers to the Axles for the shafts to print with 100% infill around the screw.
You can simply use the Objects tab in the process Section, right click on a model and replace it with the proper STL (A, B or C versions).
 

Assembly

I took care to make the overhanging hole print well (layed .2mm rectangles around it).

The Bearing Housing should click nicely around the bearing.
Then fit the “Axle Right” into the bearing hole (bearing in the housing).

To fit the nut into the left axle (shorter one), screw the nut onto the M3 20mm screw, just a bit. Then press the nut this way into axle. Depending on your fit, the nut might not be very tight and might be pushed out of its “bed” when you're inserting the screw from the other side. Just take another M3 20mm screw and use it pan head frist to keep it in place whilst screwing the parts together. 
Sorry, this might be a bit fiddly. But it's worth it! ;)

The center portion of the axle has a 0.4mm breather so the sides of the axle can grab on the inner bearing circle and pinch it. 
 

More Tips

If you cannot get a tight fit of your axle to the 8mm bearing hole, use Teflon Tape (thread type, available in any hardware store) and wrap it around the axle. It will fit super snuggly!
Also, to prevent the roller assembly from sliding on the rails from left to right, drill a hole into the rail and put an 8mm M3 screw through it, jamming the roller assembly.


If you like the design, give it a rating, leave a comment. I would appreciate it!

Enjoy!