This Bearing Assembly is a concept design which was designed for use in a CNC machine but is quite capable of being used in a 3D printer.
It is based on the use of 25mm tube (cheap and readily available) for rails and 606 bearings.
6mm rod is used for 606 bearing support and as a pivot for the 'Top' part.
An M5 cap screw and nylock nut are used for adjustment.

6/6/18 Added 608 bearing version.
14/6/18 ALL files required to build CNC machine added.
20/6/18 Minor changes to all files.
30/6/18 Minor changes to all files.

Anet A6

Doesn't Matter

Yes

0.2mm

20%

The 'Top' part requires supports under the vertical adjustment boss.
The 'Bottom' part has one very minor area which overhangs but will print without supports.

My 3D printer tends to print small holes under size so the stl files incorporate adjustments to acomodate this e.g. a required 3mm radius is input as 3.21mm.

The design was completed in SketchUp (my preferred design tool) which I find quick and easy to use despite its deficiencies when producing 'solid' and parametric models. I have made a concerted effort to adopt FreeCAD but came to the conclusion that it only works well if the intended design is initially very well detailed. By comparison SketchUp readily allows modification and gradual improvement of a less well defined design.

'stl' files exported from SketchUp are sliced with 'IdeaMaker' before printing on my highly modified Anet A6 printer.

The CNC design has an x and y movement of 400mm and a z movement of just less than 70mm. If anyone is interested in the other 3D parts required to build the CNC machine I can provide the required stl files.

30/6/18 Started using 'Onshape'; very impressed however previous comments re FreeCAD and SketchUp still apply. Will continue to use Sketchup as my primary design tool but will use Onshape for more complex stl's. The latest 'Base' and 'Top' files come from Onshape.

Search 'NevG' for other designs by this author.