Background
My D-Bot is now 5 years old. It has worked well, but the Z axis has been getting sloppy, tilting slightly as it moves up and down. I tried tightening the bearings with no improvement. A few years ago I had upgraded the X axis to using IGUS bearing surfaces, but these are not sliding as smoothly as they once did. So it was time for a linear rail upgrade and ditching the V rollers and IGUS bearings. The cost of the linear rails has come down significantly over time for these small MGN12H rails.
I had come down with Covid, so with some time on my hands, it was time for the upgrade.
Rebuild
I ordered 3 pair of 400mm long MGN12H rails and slider blocks. In addition, I needed some 2020 rail and connector pieces for the Z axis to mount the rails near the center of the Z axis sides. The 2020 rails were cut to fit to create a T shaped support structure for each side along the Y axis. This was installed and the Z motors and lead screws were moved to align with it. I was trying to minimize making radical changes to the design, so I created brackets which connect the Z linear rail bearings to the Z axis carriage. The brackets straddle the screw drive bearings. I posted the files on Thingiverse: https://www.thingiverse.com/thing:5486256 I have also included the 360 file so that you can easily modify it if necessary.
The Z brackets brackets were printed in Overture PLA Pro. This is nice and stiff. You could also use ABS. PETG is a bit too flexible (but you could always beef up the design). The rear Z axis V roller bearings were removed once the new linear rails and brackets were installed. The bed was then re-leveled.
Next comes the X and Y carriages. Prior to dismembering the X& Y carriages, it is important to 3D print the new bearing block mounts and spacers. There was an existing design on Thingiverse which worked perfectly. https://www.thingiverse.com/thing:2553737/files. I also remixed the bearing block to make a spacer that would hold the BLTouch for integrated bed leveling.
With the new bearing blocks and spacers in hand it is now time to remove the X and Y axis Vrollers and IGUS bearing blocks as well as unfasten the drive belts. The linear rails are mounted on top of the existing 2040 rails. It is then straightforward to assemble the bearing blocks, bearings and the X-Y gantry. Assembly went smoothly. The X carriage has linear rails above and below the cross beam to increase the stiffness of the printhead. I did need to add a stack of washer spacers above the BLTouch to match its height (+3mm) with the print head nozzle.
With the new parts installed it was then time to realign the bed, Zstops and BLtouch. With the alignment completed, it was time for test object prints. There is considerable improvement in the layer height and alignment and much less ringing after the edges on the printed objects.
Another successful upgrade is complete. Net cost <$130. Printer performance should now be getting close to that of a new VORON 2.4
During the rebuild, I found out that unfortunately the manufacturer of the print head I used – Micron EME Cobra is no longer in business. I was able to procure 5 more high flow nozzles however, so that should last for some time ( 3 are stainless). With stainless nozzles in hand, I can attack doing some carbon fiber+nylon parts in future projects.
Parts
400mm MGN12 H rails: https://amzn.to/3DctOn2
2020 rail 1M long 10 pack: https://amzn.to/3SgyZq4 This is much more than I needed, but now I have stock for future projects
Corner brackets for 2020 rails with M5 hardware: https://amzn.to/3VGtaW1
Hammer head drop in nuts for 2020 rails: https://amzn.to/3eOw8qH
M3,4,5,6 assorted screws : https://amzn.to/3SjIMM6
Commissions earned on Amazon Links.
Files
Z axis linear bearing mounts: https://www.thingiverse.com/thing:5486256 Includes STL and Fusion 360 CAD files
X and Y carriage linear bearing mounts: https://www.thingiverse.com/thing:2553737/files
X carriage lower spacer with mount for BLTouch sensor: