3D Printer Z-Axis Assembly
I finally finished installing the Z gantry into the new 3D printer. As expected, aligning the linear rails and lead screws was a lot of work. It took me multiple attempts to figure out how to correctly align all the Z-axis components:
The first method I tried:
- Fully assemble the Z gantry outside of the 3D printer.
- Install the Z gantry in the 3D printer.
- Adjust the positions/angles of the linear rails and lead screws to get everything parallel.
This did not work at all. I ended up with a Z gantry that was barely able to move due to misalignment and binding. It was impossible to get the alignment of all the components right. With two linear rails and three lead screws there was always something that couldn’t be mounted perfectly parallel, because the Z gantry was constraining it one way or another.
The second (successful) method:
- Individually mount the linear rails and lead screws parallel to the frame.
- Assemble the Z gantry in place in the 3D printer, piece by piece.
The advantage of this method is that the linear rails and lead screws start out parallel, and the Z gantry simply adapts its precise dimensions to the spacing between the linear rails and lead screws.
In the end, between both methods, there is only a slight difference in the final distance between the lead nuts on the Z gantry. But ultimately this slight difference seems to be the difference between misalignment + binding and smooth travel all along the Z-axis.
For both approaches a square and true 3D printer frame is necessary.
Further down on this page I have added a very rough guide of the steps involved in aligning the linear rails & lead screws and assembling the Z gantry piece by piece.
After fully building the printer I will need to repeat the alignment process myself, when I rebuild the printer with parts printed in a more temperature-resistant plastic. The temperature inside the printer will be too high for PLA after I add the external Plexiglas paneling. Because I do all prototyping with cheap PLA it is more cost effective to only print the final parts using more expensive filament. Unfortunately that means rebuilding the 3D printer at the end.
I have not decided on the exact material I will use to print the final parts, but I have my eye on polycarbonate or even carbon fiber polycarbonate filament.
Now that all the Z-axis components have been aligned, the Z gantry travels very smoothly. Especially with the 1/256 micro-step TMC2660 drivers on the Duet Wifi. There is a slight rattling audible in the video due to one of the lead screws moving around in one of the top-mounted (cheap loose-tolerance) 608 bearings. Those bearings have meanwhile been replaced with better quality ones.
Belt tensioning arms
I have had to reinforce the two belt tensioning arms that tighten the long Z-axis belt. There was a lot more tension on the belt than I anticipated. The belt tension pulled the arms upwards, out of alignment. Thickening the arm structure and adding extra mounting points solved the problem.
I also moved away from using idler pulleys with built-in bearings. Instead I switched to ‘regular’ GT2 timing pulleys and flanged bearings. The idler pulleys w/ bearings had too much runout, resulting in a wobbly timing belt.
The lead screws still need to be lubricated, and during the final rebuild I might switch to anti-backlash nuts, but I am already very satisfied with how the Z-axis runs. Of course, I will have to see if the visually smooth travel also results in high-quality prints, or if any printing artifacts show up.
A (very rough) guide to aligning the Z-axis linear rails, lead screws and Z gantry
- Lower the lead screw bearing mount on top the gantry.
- Raise the lead screw bearing mount to right above the top end of the lead screw.
- Adjusted the position of the lead screw mount at the bottom, so that the top end of the lead screw lines up exactly with the bearing in the bearing mount.
Basically, the goal is to find the lead screw mount position where the entire length of lead screw matches the (XY) position of the lead screw bearing hole. This is the position where the lead screw is parallel to the vertical frame extrusion.
After I found that position I secured the lead screw mount and the lead screw bearing mount to the frame.
This is by no means a complete guide, as several smaller steps are missing. The main idea that I want to communicate however, is that aligning the linear rails & lead screws first and then assembling the gantry seems to produce a significantly better result than vice versa.
What is next?
The next step in building the 3D printer is installing all the CoreXY components. The X- and Y-axis linear rails and carriages, stepper motors, idler pulleys, etc.