| The Z axis can use a thrust bearing to relief the tool's weight from the motor, but so do the other axes! I found that for the X-Y axes the bearings are necessary to prevent any extra linear movement due to motor's shaft and shaft/rod coupling stretching. Here is how I did it. |
| I started with a hole that is dead in the centre with the motor's shaft from the opposite side. |
| Drill a larger hole (I used a standard 35mm bit) half way through the material for the bearing. |
| Drill a larger centre hole so a nut can freely spin in it. |
| Tighten the bearing between two nuts with extra strength. The nuts should have resistance that prevents the from spining against the threaded rod, which would create linear motion. They need to spin with the threaded rod with the help of the bearing. |
| I use hot glue to create a ring around the bearing that will prevent it from moving side to side. I also create a thin outter ring on top the bearing to keep it tightly inside. |
| Finally, a piece of MDF is screwed to close the bearing inside. The rod can now freely rotate, but it cannot move linearly along the axis! |