A fully parametric, print in place Roller Bearing with cage. No supports required.

The most recent improved version of this design can be found here: https://www.thingiverse.com/thing:3201208

These are certainly not as good as real bearings, or assembled bearings e.g. using airsoft pellets but as a printed bearing are good at holding low radial loads (e.g. a filament spool) with low friction. Using lubricant (e.g. silicon lubricant) can reduce the friction even further. They are relatively easy to print (as long as your printer settings are good, see below) with little post processing. There are small overhangs on the cage, over the top of the rollers, but generally do not cause problems for printing. (the tolerance between the rollers and cage can be increased if necessary). Let me know if there are any particular parameter settings that work well together or any improvements that can be made to the design.

This was originally a proof of concept type project, to see if it could be done and is my first Open SCAD project. At the time I designed this I didn't realize there were so many other customizable bearings other than Emmetts' Gear Bearing, some of which are quite similar to this.

The unique features of this design is that it incorporates a cage which has some benefits such as reducing friction and damage between the rollers although it also reduces the load capacity of the bearing. There are other minor benefits such as keeping large bits from getting into the bearing which could possibly jam or cause damage to it. This design also has the option of rounded rollers of customizable curvature (ranging from slightly barrel shaped to practically spherical) as well as standard cylindrical rollers. This can improve it's ability to hold mixed radial and axial loads (although they are not as good as true ball bearings in this regard).

There are a large number of customizable parameters and I have not set any limits on the values you can enter in the customizer. As a result, it is quite easy to generate a bearing that won't actually work so I have assembled a checklist of the basic things to consider when customizing the bearing:

Make sure each part has sufficient area on the base to stick to the build plate. The rollers in particular can be susceptible to breaking away from the build plate if they have a very small base. Make sure the inner and outer raceways also have enough base area. You may need to increase the 'outer diameter', decrease the 'inner diameter' or decrease the 'roller diameter' to achieve this (some of the other parameters such as 'cage-raceway tolerance' or 'outer chamfer' also affect this).

Make sure there is enough space between the rollers for the cage to print in between them with at least 2 lines thickness (you may have to do trial and error by checking it in your slicer).

Make sure the raceways are not too thin (especially with curved rollers).

Make sure the cage width is set to a sensible value (0.6*'Roller Diameter' is a good starting point).

Increasing 'Cage Geometry Scale' effectively increases the thickness of the cage at its thinnest points where it wraps around the rollers on the top and bottom of the bearing. This is at the expense of the rollers and raceways however, reducing their contact area with the print bed. This also cuts into the center of the bearing, reducing the width of rolling contact.
A general rule of thumb is to increase this parameter if you have rollers larger than the default ones, or decrease it if they are smaller. Try altering the value with the default bearing to see how it affects it.

Make sure the tolerance settings are suitable for your printer. A general rule of thumb for the tolerances is 'Roller Raceway Tolerance'<'Cage Roller Tolerance'<'Cage Raceway Tolerance'.

The chamfer parameters effectively add extra tolerances on the top and bottom of the bearing, to help prevent fusing on the first few layers due to 'elephants foot'.

You can increase the mesh refinement on the raceway and rollers e.g. if making very large bearings.