After building a MendelMax and seeing the extra stability from using a bearing to hold the bottom of the Z threaded rod we decided to add a similar part for a Prusa Mendel.
We've done testing and it seems to work really great for reducing Z wobble. If you have any suggestions or findings from testing please leave them in the comments.
This mounts similar to the existing structure except for a few changes:
-The bottom center horizontal threaded rod needs to be cut shorter to 295mm
-Also the two Z drive threaded rods need to be at least 295mm.
-Two 608 bearings are needed to hold the Z drive threaded rod on the bottom.
-You will need two M8 nuts tightened together on the bottom of each Z threaded rods. This sits on top of the bearing.
The clamp is the same Prusa rod clamp used on the Z motor mount. So, you will need two extra rod clamps.