A really printer friendly roller bearing

Print-in-place mechanical things are fascinating, especially things that can actually be used for something. Maximum points for things that can't be manufactured any other way!

A ready assembled ball bearing fits all of this, but sadly it's not really possible to 3d-print a ball bearing that is anything more than a curiosity, since the balls can't be round if they are to stay in place while being printed. But roller bearings should be possible, and indeed there are lots of designs for print-in-place roller bearings here.

I have tried quite a lot of them, and one thing is immediately clear, the rollers have to be caged. Free running rollers have too much friction as the rollers are grinding against each other, and they will not roll straight causing a very jerky motion while being under load.

A good cage should keep the rollers running straight on the races, and that should in theory get rid of the jerky motion. I have tried a couple and I have always been disappointed with how they roll in practice, or they wouldn't print correctly at all due to unprintable details. One common "unprintable detail" is a curved bridge on the upper side of the cage. Another is that the roller footprint is too small to hold them in place while printing.

I always had a feeling that it should be possible to work around the limitations of 3d printing and have a design that at least in theory would work perfectly. This design at least comes closer to that. The main 'innovation' is that all bridges are straight, which should make printing much less of a hazard. Clearances are enough with margin so the cage doesn't come in contact with any of the races, nor with the roller sides, making the extra friction from the cage very low. Finally all overhangs are kept reasonable, and there are no sharp pointy overhangs that tend to curl up and cause problems.

Printing

The .stl file has the dimensions 10x42x12. I have set the clearances so it comes off the building plate more or less ready to spin, but that means it isn't very tight. But nothing is more disappointing than printing a bearing that is completely fused together, so I want to avoid that. There is also a loose stl, that have additional clearances if the first one is stuck, and a tight version that needs a little work to break free on my printer but then it runs really smooth.

It's a good idea to split the file in your slicer before slicing so each roller is sliced independently. Using e.g. triangles infill pattern in Slic3r makes a nice symmetric infill in the rollers this way.

Don't forget to set 'seam position' to 'random' (slic3r setting, something similar probably exist in all slicers), otherwise the rollers and races will have a noticeable seam on one side.

Source code included

FreeCAD source code included. The design is somewhat parametric, inner and outer diameter can be set within limits, and the width can be anything from 12mm and up. These plus the main clearances can be set from the settings spreadsheet, and the rest by modifying the sketches.

Some remixing examples:

• toy wheel: https://www.thingiverse.com/thing:3247096
• pulley wheel: https://www.thingiverse.com/thing:3253703
• spool holder: https://www.thingiverse.com/thing:3459522

A video of the spool holder in action: https://youtu.be/xqMAyEoEzUE